e-book

An Engineer’s Guide
to Current Sensing
A collection of technical content on current sensing designs

TI.com/currentsense
TI.com/technologies/current-sensing-solutions.html

Table of contents

Introduction

3

1. Current sense amplifier overview

with PWM Rejection

38

Current Mode Control in Switching Power
Systems

40

Introduction to Current Sense Amplifiers

4

Switching Power Supply Current Measurements

42

Integrating the Current Sensing Signal Path

6

Integrated, Current Sensing Analog-to-Digital
Converter

8

Increase Measurement Accuracy using
High-Speed Amplifiers for Low-Side Shunt
Current Monitoring

44

Integrating the Current Sensing Resistor

11

Common uses for Multi-Channel Current
Monitoring

5. Extending common-mode range and isolated
current measurements

13

2. Out-of-range current measurements withcurrent-sense amplifiers
Measuring Current to Detect Out-of-Range
Conditions

15

Monitoring Current for Multiple Out-of-Range
Conditions

17

High-Side Motor Current Monitoring for
Overcurrent Protection

19

46

Interfacing a Differential-Output (Isolated)
Amp to a Single-Ended Input ADC

48

Low-Drift, Precision, In-Line Isolated Magnetic
Motor Current Measurements

50

6. Current Sensing in Mobile Robots

7. Current Sensing in Collaborative and Industrial
Robotic Arms

3. Current sense amplifier application examples
Shunt-Based Current-Sensing Solutions for
BMS Applications in HEVS and EVS

Extending Beyond the Max Common-Mode
Range of Discrete Current-Sense Amplifiers21

8. How to optimize PoE systems using discrete
current sensing

12-V Battery Monitoring in an Automotive Module 23
Simplify Voltage and Current Measurementin Battery Test Equipment

25

Current Sensing Applications in Communication
Infrastructure Equpiment28

Additional resources

52

Safety and Protection for Discrete Digital Outputs
in a PLC System using Current Sense Amplifiers 30
Current Sensing in High-Power USB Type-C®
Applications

32

4. Current sense amplifiers in switching systems
Low-Drift, Precision, In-Line Motor Current
Measurements with PWM Rejection

35

High-Side Drive, High-Side Solenoid Monitor

An Engineer’s Guide to Current Sensing

2

Texas Instruments Incorporated

Introduction
Authors:
Scott Hill
Dennis Hudgins
Kurt Eckles
Mubina Toa
Zhao Tang
Guang Zhou
Dan HarmonPeter Iliya
Kevin Zhang

Designers have many options when addressing thechallenges associated with designing an accurate currentmeasurement circuit for cost-optimized applications.
Approaches range from using general-purpose operational
amplifiers to analog-to-digital converters, whether standalone or embedded in a microcontroller. This expansive
variety of approaches provides flexibility for designers ofcurrent sensing applications – allowing them specifically toaddress their unique design challenges.
This e-book was created to further simplify the current
sensing design process by helping you quickly and efficiently
narrow down the list of potential devices that align bestwith your particular system’s requirements. The current
sensing information featured in this e-book address specificapplications, focusing on identifying the most optimized
device to best serve the challenges faced in that particularapplication and offer alternative solutions that may bebeneficial for other circuit optimizations.

Maka LuoRaphael Puzio
Ben Damkroger
Kyle Stone
Arjun Prakash
Leaphar Castro
Steven LovelessTom Hendrick

Although this e-book is not an exhaustive collection ofcurrent-sensing challenges, it does address many of themore common and challenging functional circuits seen
today. If you have any questions about the topics covered
here or any other current-sensing questions, submit them to
the TI E2E™ design support forums Amplifiers forum.

An Engineer’s Guide to Current Sensing

3

Texas Instruments Incorporated

www.ti.com

Introduction

Product Overview

Introduction to Current Sense Amplifiers

Introduction

Analog Output

What are Current Sense Amplifiers?
Current sense amplifiers, also called current shunt monitors, are specialized differential
amplifiers with a precisely matched resistive gain network with the following characteristics:••••

Designed to monitor the current flow by measuring the voltage drop across a sense
element, typically a shunt resistor.
Tend to be easier to use, more precise, and less prone to noise.
Support currents from 10s of μA to 100s of A.
Natively-support common-mode voltages from –16 to +80 V and with additional circuitry up
to 100s of volts.

System Benefits Addressed by Using Current Sense Amplifiers
•
•
•

+


Integrates the full analog signal
processing and provides a voltage orcurrent output.
white
Digital Output

Real-time overcurrent protection
Current and power monitoring for system optimization
Current measurement for closed-loop feedback

Key Parameters
Common Mode Range

Offset Voltage

Gain

Temperature Stability

This specification defines the DC voltage range at the input ofan amplifier with respect to ground. Current sense amplifiers
are typically designed to support common-mode voltages wellbeyond the chip supply voltage. For example, the INA240 iscapable of supporting a common-mode voltage between –4 V to
+80 V while running on a supply as low as 2.7 V.whiteThis is a differential DC error at the input of the amplifier.
Historically, to reduce the impact of amplifiers with highoffsets, larger value shunt resistors were used to increase themeasured voltage drop. Today, TI is able to offer current sense
amplifiers with offsets as low as 10 μV, enabling higher-precision
measurements at low currents and allowing the use of smaller
value shunt resistors for improved system efficiency.white

Integrates the full signal conditioning pathand utilizes a standard two-wire digitalinterface.
white
Comparator Output
+Provides a simple ALERT signal when theload current exceeds a threshold.
white
Integrated Shunt

Current sense amplifiers come with various gain options
that have robust performance over temperature and process
variations by integrating a precisely-matched resistive gain
network. The gain options for fixed gain amplifiers vary from0.125 V/V to 1000 V/V with gain errors as low as 0.01%.white
Current sense amplifiers integrate the amplifier along withall the gain-setting resistors which enables small and unified
temperature drift. This allows for robust current measurements
across the whole specified temperature range. The achieved
temperature stability is one of the key advantages current sense
amplifiers have over discrete implementations.

SBOA534 – FEBRUARY 2022
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

+

+


Offers a low-drift, precision-integrated
sense element.
white

Introduction to Current Sense Amplifiers
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1

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Key Design Considerations

Key Design Considerations
High-Side Measurements
Sensing between supply bus and load.
System Advantages:•••

Able to detect load short to ground
Current is monitored directly from the source
High immunity to ground disturbanceBus
voltage+5 V
INA290

System Challenges:

+

•



+5 V

High bus voltage limits the availability of high input common-mode voltage devices

ADS114I 2C

Advantages Over Discrete Current Sense Circuit:•••

Integrated gain resistors provide excellent matching to enable higher performance
Reduction in board space requirements
Unique input architecture allows for the common-mode voltage to greatly exceed the device
supply voltage

LOAD

Low-Side Measurements
Sensing between the load and ground.
System Advantages:••

Simple to implement and low-cost solution
Wide range of available options

Bus
voltage

System Challenges:
•
•

LOAD

Difficult to detect load short to ground
System ground disturbance by the shunt resistor+5 V+
ADS114

Advantages Over Discrete Current Sense Circuit:••••

INA181I 2C

Integrated gain resistors provide excellent matching enable higher performance
Reduction in board space requirements
Sense a true differential measurement across the shunt resistor
Lower VOFFSET saves system power by enabling the use of smaller value shunt resistors toachieve the same error level

In-line Measurements
Sense current in-line to the load.
System Advantages:••

True phase current at all times reduces phase-to-phase errors
Best current feedback for greatest accuracy

Bus

System Challenges:••

Supply(2.7 V to 5.5 V)

PWM common-mode voltage seen by amplifier
High common-mode voltage combined with high dV/dT poses steep challenge to many
amplifiers

INA240 Advantages Over Discrete Current-Sense Circuit:•

2

M
INA240
ININ+

OUT
REF2

REF1

Enhanced PWM rejection provides high levels of suppression for large common-mode
transients (dV/dT) in systems that use PWM signals

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Application Brief

Integrating the Current Sensing Signal Path

Scott Hill

Current Sensing Products

Current is a signal that is difficult to measure directly.
However, there are several measurement methods
that are capable of measuring the effect of flowing
current. Current passing through a wire produces
a magnetic field that can be detected by magnetic
sensors (hall-effect and fluxgate for example). Current
measurements can also be made by measuring thevoltage developed across a resistor as current passes
through. This type of resistor is called a current
sensing, or shunt, resistor.
For current ranges reaching up to 100 amps on
voltage rails below 100 volts, measuring current withshunt resistors are typically preferred. The shunt
resistor approach commonly provides a physicallysmaller, more accurate and temperature stablemeasurement compared to a magnetic solution.
For the system’s current information to be evaluatedand analyzed, it must be digitized and sent tothe system controller. There are many methods
for measuring and converting the signal developed
across the shunt resistor. The most common
approach involves using an analog front-end toconvert the current sensing resistor’s differential
signal to a single-ended signal. This single-ended
signal is then connected to an analog todigital converter (ADC) that is connected to a
microcontroller. Figure 1 illustrates the current sensing
signal chain.
POWER
SUPPLYRSHUNT

SUPPLYTo optimize the current sensing signal chain, theshunt resistor value and amplifier gain must be
appropriately selected for the current range and fullscale input range of the ADC. The selection of theshunt resistor is based on a compromise between
measurement accuracy and power dissipation acrossthe shunt resistor. A large value resistor will develop
a larger differential voltage as the current passes
through. The measurement errors will be smaller due
to the fixed amplifier offset voltage. However, thelarger signal creates a larger power dissipation acrossthe shunt resistor (P = I2R). A smaller shunt resistor
develops a smaller drop across the shunt resistor
reducing the power dissipation requirements but also
increases the measurement errors as the amplifier’s
fixed offset errors become a larger percentage of thesignal.
The amplifier gain is selected to ensure that theamplifier’s output signal will not exceed the ADCs fullscale input range at the full-scale input current level.
The INA210 is a dedicated current sense amplifierthat integrates the external gain setting resistors asshown in Figure 2. Bringing these gain resistors
internal to the device allows for increased matching
and temperature drift stability compared to typicalexternal gain setting resistors. Space saving QFN
packages significantly reduce the board spacerequirements of an operational amplifier and external
gain resistors. Current sense amplifiers are commonly
available in multiple fixed gain levels to better
optimize the pairing with shunt resistor values basedon the input current and ADC full-scale input ranges.
VCM =0V to 26V

VS =2.7V to 26V
INA210+-RSHUNT

Current measurements are used in electronic systems
to provide feedback verifying operation is within
acceptable margins and to detect potential fault
conditions. Analyzing a system’s current level candiagnose unintended or unexpected operating modes
allowing for adjustments to be made to improvereliability or to protect the system components fromdamage.

VOUT

LOAD

+

ADC

CONTROLLER

-

LOAD

REF
REF

Figure 2. INA210: Current Sensing Amplifier

Figure 1. Current Sensing Signal Path
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The ADC reference will also be an additional error
source that must be evaluated in this signal path. A
typical ADC will feature an input range that is basedon the converter's reference voltage. The actualreference voltage range varies from device to device
but is typically in the 2 V to 5 V range. The LSB(least significant bit) is based on the full-scale range
and resolution of the converter. For example, a 16-bit
converter with a full-scale input range of 2.5 V, theLSB value is roughly 38 µV.
The INA226 is a specialized ADC designed
specifically for bi-directional current sensing
applications. Unlike typical ADCs, this 16-bit converterfeatures a full-scale input range of +/- 80 mV
eliminating the need to amplify the input signal
to maximize the ADC's full-scale input range. The
INA226 is able to accurately measure small shunt
voltages based on the device's maximum input offset
voltage of 10 µV and an LSB size of 2.5 µV. The
INA226 provides 15 times more resolution than theequivalent standard 16-bit ADC with a full-scale input
range of 2.5 V. The specialization of the INA226
makes this device ideal for directly monitoring thevoltage drop across the current sensing resistor as
shown in Figure 3.

Supply2.7V to 5.5V

Alert
16-BitADC

I2C
Interface

GPIO
SDA
SCL

CONTROlLER

VCM =0V to 36V

RSHUNT

Figure 1 shows the operational amplifier measuring
the differential voltage developed across the shunt
resistor and sending the amplified signal to thesingle ended ADC. A fully differential input ADC canmonitor the differential voltage directly across theshunt resistor. One drawback to using a typical ADC
is reduced input range used. The signal developed
across a shunt resistor will be small to limit the power
dissipation requirements of this component. Lower
ADC resolutions will also impact the small signal
measurement accuracy.

INA226LOAD

Figure 3. Digital Current/Power Monitor
In addition to the ability to directly measure voltage
developed across the shunt resistor as current passes
through, the INA226 can also measure the commonmode voltage. The INA226 has an input multiplexer
allowing the ADC input circuitry to switch between
the differential shunt voltage measurement and thesingle-ended bus voltage measurement.
The current sensing resistor value present in thesystem can be programmed into a configuration
register on the INA226. Based on this current
sensing resistor value and the measured shunt
voltage, on-chip calculations convert of the shunt
voltage back to current and can provide a direct
readout of the corresponding power level ofthe system. Performing these calculations on-chip
reduces processor resources that would normally berequired to convert this information.
Alternate Device Recommendations
For applications with lower performancerequirements, using the INA199 still takes advantageof the benefits of the dedicated current sense
amplifier. For applications implementing over-current
detection, the INA301 features an integrated
comparator to allow for on-chip over-current detection
as fast as 1µs. For applications with lower
performance requirements, using the INA219 is able
to take advantage of the specialized current sensing
ADC.

Table 1. Alternative Device Recommendations
DeviceOptimized Parameter

Performance Trade-Off

INA199Lower Cost

Higher VOS and Gain Error

INA301Signal Bandwidth, On-Board Comparator

Larger Package: MSOP-8

INA219Smaller Package Digital Monitor, Lower Cost

Higher VOS and Gain Error

INA190More Accurate

N/A

Table 2. Related TI Application Briefs

7

SBOA162

Measuring Current To Detect Out-of-Range Conditions

SBOA165

Precision Current Measurement On High Voltage Power RailSBOA160

High Precision, Low-Drift In-Line Motor Current Measurements

SBOA161

Low-Drift, Low-Side Current Measurements for Three-Phase Systems

Integrating the Current Sensing Signal Path

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Application Brief

Integrated, Current Sensing Analog-to-Digital Converter

Scott Hill

Current Sensing Products

The signal chain path for measuring current istypically consistent from system to system. Whether
current is measured in a computer, automobile or
motor, the common functional blocks used are foundin nearly all equipment.
The interface to a real world element such as light,
temperature or current in this case, requires a sensor
to convert the signal to a proportional value (voltage
or current) that can be more easily measured. There
are a several sensors that use magnetic field sensing
for detecting the effects of current flow. These canbe very effective for detecting very large currents orwhen isolated measurements are required. The mostcommon sensor for measuring current is a current
sensing, or shunt, resistor. Placing this component inseries with the current being measured develops a
proportional differential voltage as the current passes
through the resistor.
The remaining blocks in the signal path are selectedbased on how this measured current information is
to be used by the system. There are several blocks
that are common and found in most applications asshown in Figure 1. These blocks consist of an analog
front end (AFE) to amplify a small signal from thesensor, an analog-to-digital converter (ADC) to digitize
the amplified signal from the sensor, and a processor
to allow for the sensor information to be analyzed so
the system can respond accordingly to the measured
current level.
Power
SupplyAFE
RSHUNT+

ADC

Controller

Load

OSC

REF

Figure 1. Current Sensing Signal Chain
One requirement for the AFE is allow for directinterface to the differential signal developed acrossthe sense resistor. A single-ended output for
the AFE simplifies the interface to the following
ADC. Operational amplifiers in differential amplifier

configurations are common for this functional
requirement. Dedicated current sense amplifiers,
INA210 for example, feature integrated gain setting
components and are designed specifically for thistype of application. The INA210 has the capability toaccurately measure very small signals reducing thepower dissipation requirement of the sensing resistor.
The next signal chain block is the ADC which ispresent to digitize the amplified sensor signal. This
device can require additional external components(reference, oscillator) for more precise measurement
capability. Similarly to the AFE, there are various
options available for the ADC block. Stand-alone
converters with the onboard references and oscillators
are available as well as processors featuring onboard
ADC channels.
Both integrated and discrete ADC blocks have theirbenefits as well as limitations. Fewer components
on the board is one obvious advantage with the
ADC being integrated into the processor. Existing
instruction sets for the onboard ADC channels further
reduces the requirement for additional software
to be written to support a stand-alone ADC.
However, silicon process nodes for digital controllers
frequently are less optimized for precision analog,
limiting the performance capability of the onboard
converter. Discrete analog-to-digital converters havean advantage of allowing device selection based on
optimized performance attributes such as resolution,
noise or conversion speed.
A variation in this signal chain is to use an ADC
to measure directly across the current sensing
resistor eliminating the current sense amplifier
entirely. A standard converter would have challenges
in replacing the AFE and measuring the shunt
voltage directly. One challenge is the large full-scale
range of the ADC. Without the amplification of thesense resistor's voltage drop, either the full-rangeof the ADC cannot be fully utilized or a larger
voltage drop will be needed across the resistor.
A large voltage drop will result in a larger power
dissipation across the sensing resistor. There are
ADCs available with modified input ranges designed
for measuring smaller signals directly which canallow for direct measurement of shunt voltages.

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An internal programmable gain amplifier (PGA) is
typically integrated in these devices to leverage thefull-scale range of the ADC.
A limitation these small signal converters have is theirlimited common-mode input voltage range. These
ADCs have input voltage ranges that are limitedby their supply voltage which typically range from
3 V to 5.5 V based on the core processor voltage
being supported. The INA226, shown in Figure 2, isa current sensing specific analog-to-digital converter
that solves this common-mode limitation. This device
features a 16-bit delta-sigma core and can monitor
small differential shunt voltages on common-mode
voltage rails as high as 36 V while being powered off
a supply voltage that can range from 2.7 V to 5.5 V.
Power Supply(0V to 36V)Bus
Voltage
Shunt
Voltage

RSHUNT

INA226
16-Bit
ADC

Shunt
Bus
Current
Power
Alert

I2C
Interface

Load

Figure 2. INA226, Precision Current, Voltage,
Power Sensing ADC
Similar to the ADCs with modified small input range
capability, the INA226 has a full-scale input range ofabout 80 mV enabling the device to measure directly
across the current sensing resistor. The INA226 has
the ability to very accurately resolve small current
variations with an LSB step size of 2.5 μV anda maximum input offset voltage of 10 μV. A 0.1μV/°C offset drift ensures the measurement accuracy
remains high with only an additional 12.5 μV of offset
induced at temperatures as high as 125°C. A 0.1%
maximum gain error also enables the measurement
accuracy to remain high at the full-scale signal levels
as well.

9

While the INA226 is able to accurately measure small
shunt voltages this component has been designedwith additional functionality useful for current sensing
applications. This device features an internal registerthat is user-programmable with the specific valueof the current sensing resistor that is present on
the PCB. Having the value of the current sensing
resistor allows the INA226 to directly convert theshunt voltage measured every conversion to thecorresponding current value and stores this to an
additional output register. The INA226 also features
an internal multiplexer allowing the device to switchfrom a differential input measurement to a single
ended voltage configuration to allow for measurementof the common-mode voltage directly. The voltage
measurement, along with the previously measured
shunt voltage and corresponding current calculation,
allows the device the capability of computing power.
The device stores this power calculation and provides
this value along with the shunt voltage, current andcommon-mode voltage information to the processor
over the two-wire serial bus.
In addition to the on-chip calculations of current andpower, the INA226 features a programmable alert
register that allows the device to compare eachconversion value to a defined limit to determine
if an out-of-range condition has occurred. This
alert monitor can be configured to measure out-ofrange conditions such as overcurrent, overvoltage, or
overpower. The device also includes programmablesignal averaging to further improve measurement
accuracy.
The INA226 is optimized to support precision current
measurements. The additional features included inthis device provide the capability of supporting thesignal management and monitoring needed in thiscurrent measurement function reducing the burden on
the system processor.

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Alternate Device Recommendations

Table 1. Alternative Device Recommendations

For applications with lower performancerequirements, using the INA234 still leverages
the benefits of the dedicated current sensing
analog-to-digital converter. For additional precision
measurement capability where currents being
measured are less than 15 A, the INA260 provides
similar functionality to the INA226 while also
featuring a precision 2-mΩ integrated current sensing
resistor inside the package. For applications requiring
significantly higher common-mode voltage capability,
the AMC1305 provides onboard isolation and iscapable of supporting working voltages as high as 1.5
kV DC and handling peak transients as high as 7 kV.
For applications with lower performance requirements
for the AFE, use the INA210 to take advantage of thebenefits of a dedicated current sense amplifier.

DeviceOptimized Parameters

Performance Trade-Off

INA234Lower Cost

Higher VOS & Gain Error,
Lower VCM Range

INA260Lower System Level Gain
Error & Offset

Larger Package:
TSSOP-16

AMC1305

Isolated Measurement,
Higher Signal Bandwidth

Higher Cost, Higher VOS& Gain Error

INA210Lower Cost

Higher VOS & Gain Error

Table 2. Adjacent Tech Notes
SBOA162

Measuring Current To Detect Out-ofRange Conditions

SBOA165

Precision Current Measurement On High
Voltage Power RailSBOA167

Integrating The Current Sensing Signal
Path

SBOA170

Integrating the Current Sensing Resistor

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Application Brief

Integrating the Current Sensing Resistor

Scott Hill, Current Sensing Products
Current is one of the most common
signals used for evaluating and diagnosing
the operational effectiveness of an electronicsystem. However, measuring this signal directly isvery challenging. Instead, many types of sensors areused to measure the proportional effects that occur
due to current flowing throughout the system.
The most common sensing element used for
detecting current flowing in a system is a
resistor. Placing a resistor, called a shunt, in series
with the current path develops a differential voltage
across the resistor as current passes through it.
One common signal chain configuration for monitoringa current signal involves an analog front-end (AFE),
an analog to digital converter (ADC), and a system
controller as shown in Figure 1. An AFE, suchas an operational amplifier or dedicated current
sense amplifier, converts the small differential voltage
developed across the shunt resistor to a larger output
voltage that the ADC can digitize before sending
the information to a controller. The system controller
uses the current information to optimize the system's
operational performance or reduce functionality in theevent of an out-of-range condition to prevent potential
damaging conditions from occurring.

+

ADC

CONTROLLER

Figure 1. Current Sensing Signal Chain
The proper resistance value selection is critical in
optimizing the signal chain path. The resistancevalue and corresponding voltage developed acrossthe shunt results in a system power loss. To limit
the power loss, it is preferred to minimize the shunt
resistance. The resistor value is directly proportional
to the signal developed and sent to the current
sensing amplifier.

Amplifiers have fixed inherent errors associated withthem, input offset voltage for example, that impact
the measurement accuracy. As the input signal
increases, the influence of these internal errors on
the total measurement accuracy decreases. Whenthe input signal decreases the corresponding
measurement error is a higher . This relationshipbetween the signal level and the acceptablemeasurement accuracy provides general lower limits
for the current sensing resistor selection. The upper
limit value for the current sensing resistor should be
limited based on an application’s acceptable power
loss for this component.
One benefit of using resistors for current
measurement is the availability of accuratecomponents that provide both high precisionand temperature stable measurements. Precision
current sensing amplifiers are available featuring
measurement capabilities optimized for interfacingwith very small signals to accommodate small value
resistors and low power losses.
There are two trends for resistors as the ohmic
value decreases into the single digit milliohm leveland below. One trend for this segment of resistors
is the reduced package availability and resistor
value combinations. The other trend is the increased
cost for precision and low temperature coefficientcomponents. Pairing a low ohmic, low temperature
coefficient current sensing resistors with precision
tolerance levels (~0.1%) result in solution costs inthe several dollar range without including the costassociated with the precision amplifier.
A component such as the INA250, shown in
Figure 2, helps reduce the challenges of selecting
these increased accuracy, higher cost resistors forapplications needing precise and temperature stablemeasurements. This device pairs a precision, zerodrift, voltage output current sense amplifier witha 2mΩ integrated current sensing resistor with a
0.1% maximum tolerance and a temperature drift of
15ppm/°C over the device's entire temperature rangeof -40°C to +125°C. This device can accommodate
continuous currents flowing through the on-board
resistor of up to 15A.

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SupplyVoltage

0V to 36V
SupplyVSIN+

0V to 36V Supply

INA250
IN-

IN+

Load

VBUS

INA260

SCL

ADC

-

+

IN-

REF

OUT

ADC

GND

A0
A1

GND

SDA
SCL

GPIO

Controller

LoadController

Figure 2. Integrating The Current Sensing Resistor
In addition to the integrated precision resistor inside
this device, the INA250 also addresses one of themost common issues associated with implementing acurrent sensing solution. A low-ohmic shunt resistor isused to reduce the current sensing power dissipation.
A challenge in accommodating this low resistancevalue is the potential impact of parasitic resistance on
the PCB. Parasitic resistance in series with the shunt
resistor can cause additional measurement errors as
current flows through the resistance to create theshunt voltage. The most common source for thesemeasurement errors is poor layout techniques. A
Kelvin connection, also known as a four terminal
connection or a force-sense, is required to ensure thatminimal additional resistance is present to alter thedifferential voltage developed between the amplifier's
input pins. There are PCB layout techniques toreduce the effect of parasitic resistance, however, thisconcern is removed with the INA250.
For applications that require measuring current in ahigh dv/dt common mode transients like motor control
and solenoid control, the INA253 is specifically design
to reject PWM signals with a settling time of <10µs.
As previously described, the typical current sensing
signal chain path includes the current sensing resistor,
the analog front-end, ADC and system controller. The
INA250 combines the shunt resistor and the current
sensing amplifier. The INA260 combines the current
sensing resistor, measurement front-end and the ADC
into one single device.
Figure 3 shows the INA260 featuring the same
precision, integrated sensing resistor, pairing it witha 16-bit, precision ADC optimized for current sensing
applications. This combination provides an evenhigher performance measurement capability than the
INA250 resulting in a maximum measurement gain
error of 0.5% over the entire temperature range and amaximum input offset current of 5mA.

12

I2C
Interface Alert

I

ADC

Reference
Voltage

SDA

V

Figure 3. Integrated Signal Path
Pairing the precision, low-drift current sensing withthese precision current sensing devices provides
measurement solutions that are challenging toaccomplish using discrete amplifier and resistor
combinations. There are few catalog current sensing
resistors available that are capable of enabling the
combination of precision and temperature stablemeasurements but achieving this level of accuracy ina solution size comparable to TSSOP-16 packaged
integrated solutions doesn't exist.
Alternate Device Recommendations
For additional design flexibility, many stand-alone
current sensing amplifiers and digital power monitors
are also available. For lower performance applications
with higher current requirements than the integrated
solutions support, use the INA210 stand-alone current
sensing amplifier. For applications requiring a standalone digital power monitor, use the INA226. For
applications implementing over-current detection, theINA301 features an integrated comparator for on-chipover-current detection as fast as 1μs.
Table 1. Alternative Device Recommendations
DeviceOptimized Parameter

Performance Trade-Off

INA21035μV VOS, Package:
SC70-6, QFN-10

No on-boad current
sensing resistor

INA226

10μV VOS, Package:
MSOP-10

No on-boad current
sensing resistor

INA301Signal Bandwidth, OnBoard Comparator

No on-boad current
sensing resistor

Related Documentation
1. Integrated-Resistor Current Sensors Simplify PCB
Design2. Precision Current Measurements on High-Voltage
Power Supply Rails
3. Integrating the Current Sensing Signal Path
4. Precision, Low-Side Current Measurement

SBOA170C – JULY 2018 – REVISED MARCH 2022
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Integrating the Current Sensing Resistor
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Application Brief

Common Uses for Multi-Channel Current Monitoring

Dennis Hudgins, Current Sensing Products
As the need for system intelligence and power
efficiency continues to grow, the need for better
monitoring of critical system currents is increasingly
paramount. In the past this may have been
done with multiple operational amplifiers configured
as difference amplifiers or multiple current sense
amplifiers distributed within the system. As thenumber of current monitor channels increases sodoes the amount of external components needed torealize a solution. The added components increase
the design complexity and solution size, and candegrade the overall current sensing accuracy.
For example, consider the case where two currents
need to be measured as shown in Figure 1.
Power
Supplydevices are also more flexible in that they can monitor
voltage drops across resistors that have voltages
greater than the supply voltage.
In addition to simplifying the design process andreducing the number of external components,
having multiple current monitoring devices in asingle package facilities several common application
solutions.
For example, consider the application shown in Figure
2, where the total current drawn by the memory andprocessor is monitored by an external ADC.
+12V

INA180

IN+

DC/DC

Power
Supply+RSENSE1

OUT



LOAD1

LOAD1

IN

INA2180 Dual Current
Sense Amplifier

OP-AMP1

MemoryOUT1RSENSE1

+


2:1
MUX

OUT1

INA180

IN+

DC/DC

ADC

Control

LOAD2

LOAD2
+

RSENSE1
OP-AMP2

OUT



IN
+

RSENSE2OUT2

RSENSE2
OUT2

Figure 1. Discrete vs. Integrated Current Sensing
Solutions
In this case, the operational amplifier-based solution
requires 8 resistors to set the gain, 2 bypass
capacitors and 2 current sense resistors. The same
circuit implemented with an INA2180 only requires
the 2 current sense resistors and a single bypass
capacitor. Since the integrated gain-set resistors arewell matched, the accuracy of the INA2180 solution
is much better than what can be achieved in acost effective discrete implementation. The integrated
gain-set resistors permit higher accuracy monitoringor allow use of a cheaper wider tolerance current
sense resistor. The INA2180, INA2181, and INA2290

Other
Loads

Processor

Figure 2. Monitoring Total Current in Two Supply
Rails
One approach would be to monitor both the CPU
and memory current, multiplex the current to an
ADC and then and add the resulting values together
in a microprocessor. This approach requires somemathematical processing as well as an ADC tocontinually sample outputs at a fast enough rate tobe effective. A better approach would be to use the
REF pin of the INA2181 to add the current drawn by
the memory to the current drawn by the CPU. Thiscan be done by connecting the output of channel 1that monitors the memory current to the REF2 pin asshown in Figure 3.

SLYA024A – DECEMBER 2017 – REVISED SEPTEMBER 2021
Common Uses for Multi-Channel Current Monitoring
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13

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+12V

Power
SupplyINA2181
REF1

IN+1

INA2181
IN+1

DC/DC

+

RSENSE+RSENSE

Memory

OUT1



OUT1



IN1

IN1

LOAD

REF2

IN+2

IN+2

DC/DC

REF2

+

RSENSE+RSENSE

OUT2



OUT2



ADC

ADC
IN2

Other
Loads

GND

ProcessorIN2

VOUT2 = VREF1 if there is no leakage current

GND

VOUT2 = (ILOAD1 + ILOAD2) × RSENSE × GAIN

Figure 3. Analog Current Summing With INA2181
The channel 2 output will be the amplified sum of
the currents from the CPU and memory. The current
from the memory and the current from the total canbe monitored when desired by an ADC. However,since the channel 2 output is an analog signal, acomparator with an appropriately set reference canbe used to interrupt the system when an over current
condition occurs. For this circuit to function properly
the values of the two sense resistors must be thesame.
Another convenient use for multi-channel current
monitors is to detect unexpected leakage paths.
These leakage paths could be caused by unintended
shorts to ground or some other potential not in thecurrent measurement path. One technique to detectleakage current paths is to monitor all current going
into and coming out of a circuit. As long as there
are no unexpected leakage paths, the current into theload must equal the current coming out. To detectleakage currents all current in and out of a circuit
should be monitored. If the currents in and out are
equal, no unexpected current leakage path will be
detected. Use of the dual current monitor provides
a simple technique to detect leakage current paths
without the need for multiple devices or the need toexternally add or subtract currents. The circuit shownin Figure 4, uses the INA2181 to monitor the current
into and out of a load.
By reversing the polarity of the resistor connections of
the second amplifier and connecting the output of thefirst amplifier to the second amplifier, the current goingin to the load is subtracted from the current going out.

14

VREF1

REF1

Figure 4. Current Subtraction Using the INA2181,
for Leakage Current Detection
If the voltage at OUT2 is equal to the appliedreference voltage then no leakage path exists. If
VOUT2 is higher than the applied reference voltage
then there is unexpected current leaving the load.
Likewise if VOUT2 is below the reference voltage thenunexpected leakage current is entering the load. As
before, for this circuit to function properly the values of
the current sense resistors must be the same.
Texas Instruments offers several solutions for
multichannel current monitoring. To monitor 4channels the INA4180, INA4181, and INA4290
devices are available with an analog voltage output.
The INA3221 provides the ability to accurately
measure both system current and bus voltages for up
to 3 independent channels. The values of the currents
and voltages are reported through an I2C interface.
Table 1. Alternative Device Recommendations
DEVICE

OPTIMIZED PARAMETERSPERFORMANCE TRADE­
OFF

INA4180

4-channel analog current
monitor

Unidirectional Measurement

INA4181

Bidirectional 4-channel
current monitor

Larger package

INA32213-channel digital current/
voltage monitor

No analog output

INA22902-channel, 120-V analog
current monitor

Unidirectional Measurement

INA42904-channel, 120-V analog
current monitor

Unidirectional Measurement

Table 2. Adjacent Tech Notes
LITNUMBERTITLE

SBOA162

Measuring Current To Detect Out-of-Range
Conditions

SBOA169

Precision, Low-Side Current Measurement

SBOA190

Low-Side Current Sense Circuit Integration

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Common Uses for Multi-Channel Current Monitoringwww.ti.com

Application Brief

Application Brief

Measuring Current To Detect Out-of-Range Conditions

Scott Hill, Current Sensing Products

There is a time-current dependency that limits theeffectiveness of a fuse in responding to a specificcurrent threshold. An example time-current responseof a fuse is shown in Figure 1.
10,00020A Fuse
Rating

1,000

TIME (s)100A Fuse
Rating

10

1
0.1

0.01

1

10

RPULL-UP

VS
IN+

IN-

GNAL

INPUT SI
ALERT

CMP

LIMIT
Load

THRESHOLDRLIMIT

ALERT

Figure 2. INA300 Over-Current Comparator
Figure 2 shows the INA300 measuring the differential
voltage developed across a current sensing resistor
and the comparison to a user-adjustable thresholdlevel. The alert output is pulled low when thethreshold level is exceeded. The INA300’s alert
response is issued following a current excursion in as
short as 10µs.
There may also be a need to provide information
on how much current is actually being pulled by the
supply or a particular load in addition to the fault
indication. For these requirements a typical approachis to utilize a combination of a current sense amplifier
and a stand-alone comparator as shown in Figure 3.

45A Fuse
Rating100+2.7 V to 5.5 V

Power Supply(0 V to 36 V)

INPUT

Fuses are commonly used for short-circuit protection
preventing damaging levels of current from flowing
in the system. In an out-of-range event the fuse willblow and break the circuit path. The fuse must be
replaced for the system to operate correctly again. In
worst case situations the system requires delivery to a
repair facility if the fuse is not easily accessible.

The INA300 is a specialized current sensing
comparator with the ability to perform the basic
comparison to expected operating thresholds requiredfor out-of-range detection.

OUTPUT

There are multiple methods available to diagnose fault
conditions in a system depending on how the out-ofrange indication is intended to be used. One method
is to monitor an entire system's current consumption
to identify potentially damaging excursions for the
power supply. In this case, measurement accuracy
is typically not critical and requires a simple alert toindicate an out-of-range condition.

Another overcurrent protection scheme becoming
more common is to allow the system to protect
itself when an excursion is detected but then enable
the system to return to normal operation once thefault condition has been cleared. This protection
method uses a comparator comparing the monitored
operating current levels to defined thresholds, looking
for out-of-range conditions. Creating the necessarylevel of detection for a particular application relies
on system specific variables such as the adjustabilityof the desired over-range threshold, the amount ofmargin acceptable in the threshold level and how
quickly the excursion must be detected.

RSHUNT

The amount of current flowing throughout a systemprovides insight in determining how effectively thesystem is operating. A basic insight into the system's
operation is a comparison between the current being
pulled from a power supply and a pre-defined target
range for that particular operating condition. Current
levels exceeding the expected current level indicatethat an element in the system is consuming more
power than expected. Likewise, if the current is lower
than expected it may indicate some part of the system
is not powered correctly or possibly disconnected.

100

CURRENT (A)1,000

10,000Figure 1. Typical Time-Current Fuse Curve

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Measuring Current To Detect Out-of-Range Conditions
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Application Brief
SUPPLYRPULL-UP+
RSHUNT

GPIO-

CONTROlLER

POWER
SUPPLY

+
LOAD

REF

Figure 3. Discrete Over-Current Detection
The current sense amplifier measures the differential
voltage developed across the sense resistor andsends the output to both the comparator input andanalog to digital converter (ADC).
The INA301 and INA381 combines both the current
sense amplifier (providing a voltage output signal
proportional to the measured input current) and an
on-board comparator (for over-current detection) into
one device as shown in Figure 4.
Power Supply
0V to 36V

2.7V to 5.5V
INA301

RPULL-UP

+

CMP

ALERT

Load

LIMIT

Power Supply
0V to 26V

RSHUNT

THRESHOLDVOUTRLIMIT

2.7V to 5.5V
VS

IN+

INPUT

VOUT

IN-

OUTPUTRSHUNT

VSIN+

INA381

RPULL-UP

+

VOUT

INCMP

Load

CMPREF

ALERT
+5 V

ALERT

Figure 4. Integrated Over-Current Detection with
INA301 and INA381
With both the current information and an out-of-range
indicator the system may utilize multiple monitoringand protection schemes based on the operating
conditions. One scheme used with this device is toinitially monitor only the alert indicator as a fault
indicator. Once an out-of-range condition is detected
and the alert pin is asserted, the system then begins
actively monitoring the analog output voltage signal
allowing the system to respond accordingly. The
system response typically will be to reduce system
performance level, shut down entirely or to continue
monitoring to determine if the excursion continues tobecome a more significant system concern. Having
both the proportional output voltage as well as the
on-board over-current detection function allows thesystem to only actively monitor the current information
when necessary optimizing system resources. The
INA381 is similar in function to the INA301 except
both inputs to the over-current comparator are directly
accessible for greater flexibility when setting the overcurrent trip threshold.

16

The INA301 provides a combination of performancecapability in addition to the integration of boththe current sensing amplifier as well as on-board
comparator. The INA301 amplifier's has a small
signal bandwidth of 450 kHz at a fixed gain of
100 (gains of 20 and 50 are also available) and amaximum input offset voltage of 35 µV. In addition
to the maximum gain error specification of 0.2%, theamplifier's ability to detect the out-of-range condition
is fast. The INA301 is able to achieve accurate input
measurements and quickly respond to over-current
events with a response time including the input signal
measurement, comparison to the user-selected alertthreshold, and assertion of the comparators output inless than 1µs.
Alternate Device Recommendations
For applications needing to monitor current on
voltage rails that are higher than the INA301's rangeof 36V with the on-board over-current detection,
use the INA200. The INA180 is a current sense
amplifier that is commonly used in the discrete overcurrent detection circuit using an external comparator.
The INA381 provides a cost effective solution forover current detection in applications that feature acommon mode range less than 26 V. For applications
requiring monitoring of a second fault thresholdlevel, the INA302 features an additional out-of-range
comparator with dedicated adjustable threshold level.
Table 1. Alternate Device Recommendations
DeviceOptimized Parameter

Performance Trade-off

INA180

Package: SC70-5,
SOT23-5

Reduced bandwidth,
analog output only

INA381

Cost, Flexibility

Reduced bandwidth,
Common mode voltage

INA200Common-mode Voltage
Range: -16 V to +80 V

Reduced accuracy

INA302

Two Independent Alert
Comparators

Larger Package:
TSSOP-14

Related Documentation
1. Low-Drift, Low-Side Current Measurements for
Three Phase Systems
2. High-Side Motor Current Monitoring for OverCurrent Protection
3. Integrating The Current Sensing Signal Path
4. Monitoring Current for Multiple Out-of-Range
Conditions
5. Safety and Protection for Discrete Digital Outputs
in a PLC System Using Current Sense Amplifiers

Measuring Current To Detect Out-of-Range Conditions
Copyright © 2022 Texas Instruments Incorporated

SBOA162D – MAY 2018 – REVISED MARCH 2022
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Design Guide: INA300 INA301 INA302 INA303

Monitoring Current for Multiple Out-of-Range Conditions

Dennis Hudgins, Current Sensing Products

Being able to quickly know when a current level isout of range allows improved safely, improved system
intelligence/diagnostics and reduced downtime.
To address the response time required for out-ofrange current conditions, analog comparators areneeded to detect when the current exceeds a givenreference threshold. However, in many cases having
only one alert level is insufficient to determine
the system status and provide appropriate system
responses to out-of-range currents. To handle thisrequirement the circuit shown in Figure 1-1 canbe used to monitor multiple out-of-range current
conditions.
SUPPLYREF1+-

ALERT1GPIO1CONTROlLER

POWER
SUPPLY+RSHUNT

SUPPLYLOAD-+

ALERT2

GPIO2

REF2

Figure 1-1. Discrete Implementation to Detect
Multiple Over-current Events
This circuit is composed of 5 devices: a current sense
amplifier, two comparators, and two references. The
discrete implementation, shown in Figure 1-1 requires
careful selection of the comparators to get the desired
alert response time. Slow response times may notallow enough time for the system to take action; while
SBOA168C – MAY 2018 – REVISED OCTOBER 2021
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too fast of a response time can trigger false alerts,
possibly resulting in system shutdown.
Figure 1-2 shows a simpler circuit that addresses thedesign issues present in the discrete implementation.
2.7V to 5.5V

SupplyVS

CMP

LIMIT1RLIMIT 1

LATCH1IN++

Fault Threshold

RPULL-UP
ALERT1INPUT

Power Supply
0V to 36V

Warning Threshold

INPUT SIGNAL

OUT
SupplyIN-

RPULL-UP
CMP

Load

ALERT2
LIMIT2

RLIMIT 2

DELAY
GND

LATCH2VOUTOUTPUT

One of the first parameters engineers look at when
determining proper operation of a PCB design isthe operating current. By examining the operating
current, an engineer can immediately tell if something
on the board is shorted, whether any of the devices
are damaged, and in some cases detect if thesoftware is running as expected. The traditional
approach of using a current sense amplifier + ADC
to monitor current for out-of-range conditions does notprovide the required alert response time. Also, useof an ADC to monitor over current alert thresholds
requires constant communication between the ADC
and host processor which can unnecessarily burden
the system.

ALERT1ALERT2

CDELAYtDELAY

Figure 1-2. INA302 Multi-Alert Over-Current
Comparator
The INA302 incorporates the ability to detect two outof-range conditions. The lower out-of-range condition
is referred to as the over current warning threshold,while the higher out-of-range condition is referred
to as the over current fault threshold. The overcurrent warning threshold allows detection when thecurrent is starting to get too high but has not yet
reached the fault threshold where system shutdown
may be initiated. When the current exceeds thewarning threshold, the system may opt to reduce thesystem power consumption by disabling sub-circuits,
controlling supply voltages, or reducing clocking
frequencies to lower the total system current toprevent a fault condition. If an over-current fault
condition does occur, it is important to respond quickly
to prevent further system damage or malfunctioning
behavior.
To minimize the component count and facilitate easeof use, the alert thresholds of the INA302 are set
with single external resistors. The fault thresholdshould be set higher than the worst case current
the system could be expected to consume. Whenthe current exceeds this threshold, the alert pin of
the INA302 will respond within 1 μs. The value forthe warning threshold is application dependent, but is
usually higher than the nominal operating current. The
response time of the warning threshold is adjustablewith an external capacitor from 3 μs to 10 s.
By setting the warning threshold delay time
appropriately, it is possible to set the over-current
Monitoring Current for Multiple Out-of-Range Conditions

Copyright © 2021 Texas Instruments Incorporated

17

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Another use of under-current detection is to provide
confirmation of proper system status. Some systems
go into low power modes where the current is below
the normal operating range. In this case, the undercurrent alert output can be used to notify the host thatthe system has indeed entered the shutdown state.
Some designs may only care to get notified if thecurrent is outside of expected operating bounds. For
these cases, the INA303 can be configured to run
in window mode by connecting the two alert outputs
together as shown in Figure 1-4. In this mode, thesingle alert output will be high as long as the current is
with-in the normal operating window.
Power Supply
0V to 36V

In some systems it is beneficial to detect when thecurrent is too low. For these applications, the INA303,
shown in Figure 1-3 provides both over and undercurrent detection.

CMP

LIMIT1RLIMIT 1++

INPUT SIGNAL

OUT
VOUT

IN-

CMP

ALERT2
LIMIT2

RLIMIT 2

DELAY
GND

Under-Current
Threshold

INPUT SIGNAL

SupplyALERT

RLIMIT 1

LATCH1IN+

ALERTLATCH2

Figure 1-4. INA303 Window mode Operation

OUT

IN-

NormalOperatingRegion

RPULL-UP
ALERT1

LIMIT1

RPULL-UP
ALERT1LATCH1IN+

CMP

Over-Current
Threshold

SupplyVS

SupplyVS

Load

2.7V to 5.5V

INPUT

Power Supply
0V to 36V

2.7V to 5.5V

INPUT

Some systems allow operation above the warning
threshold for a period of time before triggering analert. One such application is monitoring the supply
current to a processor. The processor may beallowed to operate above the normal maximum
current level for a brief period of time to maximize
computing throughput during critical operations. If thecurrent is above the warning threshold when the set
delay expires the alert output will pull low to notify thehost processor so the voltage or clocking frequency
can be decreased before overheating occurs.

In this case, the alert output can notify the system ofthis condition and fault handling procedures can be
implemented before system failure.

OUTPUT

warning threshold closer to the maximum DC
operating current while still avoiding false trips due
to brief current spikes or noise. Wider separation
between the fault and warning thresholds provides thesystem additional time for preventative action before
the fault threshold is exceeded.

VOUT

CMP

Load

ALERT2
LIMIT2

RLIMIT 2

DELAY
GND

LATCH2OUTPUT

RPULL-UP

Alternate Device Recommendations

ALERT1ALERT2

CDELAYtDELAY

Figure 1-3. INA303 Over and Under Current
Detection
When the current exceeds the over current fault
threshold, the ALERT1 output will respond within 1
μs. However, if the current goes below the undercurrent threshold, the ALERT2 response time is set
by the delay capacitor. Undercurrent situations may
briefly occur in normal operation; however, if thiscondition persists, it could be due to a damaged
device or system that is about to fail.

The INA226 can be used in applications that require
digital current monitoring. If only a single digital alert
output is needed, the INA300 provides an optimal
solution in a tiny 2mm x 2mm QFN package. For
applications that only require a single alert output in
additional to the analog current signal, the INA301
provides excellent current monitoring accuracy withan alert response less than 1 μs. For cost sensitive
applications and added flexibility, the INA381 provides
an current sense amplifier with an internal comparator
with accessible inputs.

Table 1-1. Alternate Device Recommendations
DeviceOptimized Parameter

Performance Trade-off

INA301MSOP-8 package, single alert with analog monitor.

Single alert

INA3002mm x 2mm QFN package

Alert only

INA381

Cost effective, accessible comparator inputs

Single alert

INA226

Digital current monitor

N/A

Table 1-2. Related TI Application Briefs

18

SBOA162

Measuring Current To Detect Out-of-Range Conditions

SBOA163

High-Side Motor Current Monitoring for Over-Current Protection

SBOA167

Integrating The Current Sensing Signal Path

SBOA193

Safety and Protection for Discrete Digital Outputs in a PLC System

Monitoring Current for Multiple Out-of-Range Conditions
Copyright © 2021 Texas Instruments Incorporated

SBOA168C – MAY 2018 – REVISED OCTOBER 2021
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www.ti.com

Tech Note

Application Brief

High-Side Motor Current Monitoring for Overcurrent
Protection

Scott Hill, Mubina Toa, Current Sensing ProductsHigh power, precision motor systems commonly
require detailed feedback such as speed, torque andposition to be sent back to the motor control circuitry
to precisely and efficiently control the motor’soperation. Other motor control applications, such as
fixed motion tasks, do not require the same level ofsystem complexity to carry out their jobs. Information
alerts that the motor had stalled, an unintended object
was found in the motor's path, or that a short was
detected in the motor's winding can be sent back to
the motor control circuitry. More complex motor
control systems implementing dynamic control andactive monitoring can also benefit from adding simple
out-of-range detection function because of the fasterindication of out-of-range events.
By placing a current sense amplifier in series with the
DC power supply driving the high side of the motor
drive circuitry as shown in Figure 1, the overall current
to the motor can be measured easily detecting out-ofrange conditions. To detect small leakages the lowside return current can also be measured. A
difference between the high-side and low-side current
levels indicates a leakage path exists within the motor
or motor control circuitry.

RSHUNTRSHUNT
Figure 1. Low & High-Side Current Sensing
The DC voltage level varies depending on the voltage
rating of the motor leading to multiple current
measurement solutions to accommodate thecorresponding voltage levels. For low-voltage motors(approximately 5-V), the selection of circuitry tomonitor this current is much simpler with multiple
amplifier types (current sense, operational, difference,
instrumentation) and can perform the current

SBOA163B – JULY 2016 – REVISED FEBRUARY 2021
Submit Document Feedback

measurement function to support this common-mode
input voltage range.
For larger voltage motors (24-V and 48-V, forexample), the available options reduces to dedicatedcurrent sense and differential amplifiers. As thevoltage requirements continue to increase,measurement errors begin to impact the ability toeffectively identify out-of-range conditions. One
specification that describes an amplifier's
effectiveness at operating at high input voltage levels
is the common-mode rejection (CMR) term. This
specification directly describes how well an amplifier's
input circuitry can reject the influence of large input
voltages.
Ideally, an amplifier is able to completely reject andcancel out any voltage common to both input pins andamplify only the differential voltage seen between
them. However, as the common-mode voltage isincreased, leakage currents in the amplifier's input
stage result in additional input offset voltage. Larger
input range levels being monitored will create
proportionally larger measurement errors.
For example, an amplifier (difference amplifier orcurrent sense amplifier) that has a CMR (CommonMode Rejection) specification of 80 dB will have asignificant offset voltage introduced in themeasurement based on the input voltage level. An 80dB CMR specification corresponds to an additional
100 µV of offset voltage induced into themeasurement for every volt applied to the input.
Many devices are specified under defined conditions(VCM = 12 V and VS = 5 V, for example) which
establishes the base-line for the default specifications(CMR and PSRR, specifically). In this example
operating at 60-V common-mode voltage creates achange in VCM of 48 V (60 V – 12 V). A 48-V changewith a 80-db CMR results in an additional 4.8 mV ofoffset voltage in addition to the specified input offset
voltage found in the device’s data sheet.
Applications employing calibration schemes are lessconcerned by this additional induced offset voltage.
However, for applications where system calibration

High-Side Motor Current Monitoring for Overcurrent Protection
Copyright © 2021 Texas Instruments Incorporated

19

www.ti.com

Tech Note

The INA240 is a dedicated current sense amplifier
with a common-mode input voltage range of –4 V to
+80 V and a worst-case CMR (Common-Mode
Rejection) specification of 120 dB over the entire input
and temperature range of the device. 120 dB of CMR
corresponds to an additional 1 µV of input offset
voltage induced for every 1-V change in commonmode voltage. The temperature influence on theamplifier's ability to rejection common-mode voltages
is not well documented in many product data sheets
so it should be evaluated in addition to the room
temperature specification. The INA240 maintains aensured 120-dB CMR specification over the entire –40°C to +125°C temperature range. The typical CMR
performance for the INA240 over the entire
temperature range is 135 dB (less than 0.2 µV for
every 1-V change) as shown in Figure 2.

Figure 2. Common-Mode Rejection vs.
Temperature
A system controller has the ability to use the current
sense amplifier's measurement to evaluate theoperation of the system. Comparing the current
information to pre-defined operating threshold allows
for detection of out-of-range events. A comparator
following the high-side current sense amplifier caneasily detect and provide alerts quickly to the systemallowing for corrective actions to be taken.
Figure 3 illustrates the signal chain path for monitoringand detecting out-of-range excursions whenmeasuring currents on a high-voltage rail driving the
motor drive circuitry. The output signal proportional tothe measured input current is directed to the ADC in
addition to be sent to the comparator to detect
overcurrent events. The comparator alert will assert if
the input current level exceeds the predefined
threshold connected as the comparators reference
voltage.

range conditions. A fast signal bandwidth device, suchas the INA290, enables speedy response to a control
unit to ensure other critical system components are
not damaged by the unintended excess current
flowing in the system. The INA290 is a 1.1-MHz partwhich can measure on the high-side between 2.7-V to
120-V common mode.
SUPPLYVCM =-4V to +80V

RPULL-UP+

RSHUNT

GPIO-

CONTROlLER

cannot account for this shift in offset, selection of anamplifier with better common-mode voltage rejection
is required.

+

REF

Figure 3. High-Side Overcurrent Detection
Alternate Device Recommendations
If a comparator is required, the INA301 is a good
option as it is a precision current sense amplifier withan onboard comparator that is ideal for detecting
overcurrent events on common-mode voltages up to
36 V. For applications requiring higher voltage
capability, the INA149 is a high performancedifference amplifier capable of interfacing with
common-mode voltages up to ±275 V off of a ±15-V
supply and has a ensured CMR of 90 dB (or 31.6 µV
for every 1-V input change). If isolation or high voltage
common-mode capability is required, the TMCS1100,
hall-effect current sensor, has ±600 V of basic
isolation.
Table 1. Alternate Device Recommendations
DEVICE

OPTIMIZEDPARAMETERPERFORMANCETRADE-OFFS

INA290

Package: SC-70, Signal
Bandwidth (1.1 MHz)

High-side only (2.7 Vcm
to 120 Vcm)

INA149VCM Range: ±275 V

CMR, Gain

INA301

Onboard Comparator;
35 µV VOSVCM: 0 V to 36 V

TMCS1100±600-V basic isolation

Not as accurate as ashunt-based solution

Table 2. Related TI Application Briefs
LITERATURE
NUMBERTITLE

SBOA160

High Precision, Low-Drift In-Line Motor
Current Measurements

SBOA161

Low-Drift, Low-Side Current Measurements
for Three-Phase Systems

SBOA162

Measuring Current To Detect Out-of-Range
Conditions

SBOA165

Precision Current Measurement On High
Voltage Power RailA key requirement for overcurrent detection circuitry is
the ability to detect and respond quickly to out-of20

High-Side Motor Current Monitoring for Overcurrent Protection
Copyright © 2021 Texas Instruments Incorporated

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TI Tech Note

Application Brief

Shunt-Based Current-Sensing Solutions for BMS
Applications in HEVs and EVs

Guang Zhou and Dan Harmon
BMS Topologies and Current Measurement
Methodologies
Hybrid electric vehicles (HEV) and electric vehicles(EV) continue to gain share in the overall global
automotive market. The battery management system(BMS) for these vehicles carries out the importanttasks of keeping the battery inside the safe operatingarea (SOA), monitoring power distribution, andtracking the state of charge (SoC). In a typical HEV
and EV, both high- and low-voltage subsystems arepresent. The high-voltage subsystem operates atseveral hundred volts, and interfaces directly withutility grid or high-voltage DC sources. The lowvoltage subsystem generally operates at 48 V and 12
V.
400-V and 800-V
Charger

12-V Conversion

48-V Load
Non-isolated
CSA

Non-isolated
CSA

12-V Load

Non-isolated
CSA

Isolated
CSA

High-Voltage Load

ISOLATION

48-V Conversion

Non-isolated
CSA

Non-isolated
CSA

Figure 1. Topologies of Current Sensing in BMS
High-voltage battery, top-of-stack measurements
require an isolated solution. Magnetic solutions
enable the require isolation, but typically will not beable to support the full current range. TI offers isolated
shunt-based current sensing solutions, such as the
AMC3301-Q1. A summary of other examples ofisolated current sensing technology can be found in
the Comparing Shunt- and Hall-Based Isolated
Current-Sensing Solutions in HEV/EV application
brief. Isolation is not typically required for top-of-thestack 48-V or 12-V battery systems nor in bottom-ofthe-stack implementations.

The focus in this document is on non-isolated, shuntbased current-sensing amplifiers (CSA), also calledcurrent shunt monitors (CSM), and digital powermonitors (DPM) for bottom-of-stack or top-of-stack in
12-V to 48-V BMS subsystems. The advantages of
non-isolated shunt-based current sensing include
simplicity, low cost, excellent linearity, and accuracy. A
drawback of shunt-based current sensing is the power
dissipation requirements for the shunt resistor at the
maximum current levels.
Current Sense Amplifiers in an HEV or EV Charger
Battery array is an important component of any HEV
or EV. There are mainly two types of rechargeable
batteries: the lead acid battery that has been aroundfor over 100 years, and the Li-Ion battery that has only
been put into practical use since the 1980s. Both leadacid and Li-Ion batteries follow a certain constantvoltage-constant current charging profile. The CSA
plays an important role in making sure the battery
remains within the SOA.
Operational current for the traction inverter andcharging current can be greater than 1000 A in manysystems. However, these BMS systems must also beable to measure currents equal to or less than 1 A
when the vehicle is off as many systems continue tofunction such as keyless entry or vehicle-to-worldcommunications. BMS systems must monitor the
power distribution as accurately as possible during
both operation and vehicle off-state to provide overallsystem health and safety information. State of charge(SoC), which is the equivalent of a fuel gauge for thebattery pack in an HEV or EV, correlates to driving
range. Current sensing is one of the important
methods to determine SoC. In addition to theprecision monitoring of the battery, most automotive
BMS systems will require a redundant measurementwith relaxed accuracy requirements to enable systemlevel functional safety goals.
The extreme difference between the traction motor
current (>1000 A) and the off-vehicle communications
current (<1 A) creates a multi-decade, high-precision,
bidirectional (charging versus vehicle operation)
current measurement challenge.

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TI Tech Note

Sizing the Shunt Resistor
Historically, measuring the high current with shuntbased topologies has been challenging. However,with the availability of ultra-low resistance shunts, theoption is now viable. A typical analog current sense
amplifier will have a fixed gain between 20 V/V and
200 V/V and operate from a 5-V supply. This 5-V
supply determines the maximum output voltage(ignoring swing to supply limitations), and when we
divide by the two gain extremes, we get a full-scale
input voltage range of 250 mV to 25 mV. Assuming abidirectional maximum current measurement of ±1000
A, we can calculate a maximum shunt value of 125µΩ to 12.5 µΩ. As discussed in the TI Precision Labs
- Current sense amplifiers videos, the amplifier offset
will dominate the offset error at the low current range.
If we use the ultra-precise INA240-Q1 with an offset of
25 µV, we get an error of 20% and 200% respectively
on the two shunt resistors. Table 1 summarizes thesecalculations along with the power dissipation acrossthese shunts at 1000 A.
Table 1. INA240-Q1 Shunt Resistor Value, Offset
Error, and Power Dissipation Calculations for±1000-A BMS Application
GAIN OPTION

INA240A1: 20 V/V

INA240A4: 200 V/V

Full scale input

250 mV

25 mV

Maximum shunt

125 µΩ

12.5 µΩ

Offset error at 1 A

20%

200%

PDIS at 1000 A

125 W

12.5 W

Solving the Multi-Decade ChallengeThis is where an ultra-precise, low-offset solution isrequired. TI’s DPMs are specialized analog-to-digitalconverters (ADC) dedicated to measuring current.
Most can also monitor bus voltage and can calculate
the power as well. The full-scale input range is scaled
down from that of a typical ADC to accommodate thetypical small signal voltage drop across a shunt
resistor. The INA229-Q1 (SPI Interface) and INA228Q1 (I2C interface) are 20-bit DPMs with VOFFSET = 1µV and a ±163.84-mV full-scale input range. Having adefined full-scale input range makes calculating the
maximum shunt resistor value fairly straight forward,
simply divide the full-scale input by the maximum
current: 163.84 mV ÷ 1000 A = 163.84 µΩ. A morecommonly available 100-µΩ shunt resistor is used to
calculate a 1% error at 1 A.

mA on a 100-µΩ shunt resistor, well below the target
minimum current level of 1 A.
If even lower current levels are needed to beaccurately measured, system calibration may become
necessary. Zero-drift devices enable single-pointcalibration, and make such challenging designs
possible by offering stable performance overtemperature.
For current sensing in HEV and EV BMS subsystems,
the INA229-Q1 or INA228-Q1 are excellent choices
for any bottom-of-stack implementations or top-ofstack implementations in 48-V or 12-V systems withan 85-V common-mode specification and ultra-low
offset of ±1 µV. The industry standard digital interface
can further simplify the design by taking advantage ofan existing communication bus. The INA240-Q1 with
its 80-V common mode voltage range could be usedin 48-V system top-of-stack measurements for either
the redundancy implementation or in applications
requiring less total dynamic range. All three devices
are manufactured with TI proprietary Zero-Drifttechnology, which enable single temperature
calibration, if needed, to address lower current
accuracy.
Automotive Device Recommendations
In addition to the INA229-Q1 and INA228-Q1, TI
offers other digital output current, voltage, and powermonitors. Some example products and adjacenttechnical documents are compiled in Table 2 andTable 3.
Table 2. Alternative Device Recommendations
DEVICEDIGITAL
INTERFACEDESCRIPTION

INA239-Q1

SPI

85-V, Bidirectional, Zero-Drift, 16-Bit,
Low- or High-Side, SPI Current/Voltage/
Power Monitor

INA238-Q1

I2C, SMBUS

85-V, Bidirectional, Zero-Drift, 16-Bit,
Low- or High-Side, I2C Current/Voltage/
Power Monitor

INA226-Q1

I2C, SMBUS

36-V, Bidirectional, Zero-Drift, 16-Bit,
Low- or High-Side, I2C Current/Voltage/
Power Monitor

Table 3. Adjacent Tech Notes
LITERATURE
NUMBER

LITERATURE TITLE

SBAA325

Current Sensing With INA226-Q1 in HEV/EV Low
Voltage BMS Subsystems

SBOA170

Integrated, Current Sensing Analog-to-Digital
Converter

The final error check is to verify that the integrated
ADC is capable of resolving a signal level less thanthe offset error level. The INA228-Q1 and INA229-Q1
feature a 20-bit delta-sigma converter with one bit
being the sign bit. Dividing the full-scale input of
163.84 mV by 19 bits of resolution results in 312.5 nV
per least significant bit (LSB). This corresponds to 3.1
22

Shunt-Based Current-Sensing Solutions for BMS Applications in HEVs and
SBAA324B – DECEMBER 2018 – REVISED FEBRUARY 2021
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Application Brief

12-V Battery Monitoring in an Automotive Module

Peter Iliya
Monitoring current off an automotive 12-V battery
provides critical data for a variety of applications suchas module current consumption, load diagnostics, andload feedback control. The TI current sensing portfolio
can address this space with analog and digital current
sense amplifier (CSA) devices that come automotive
qualified, contain integrated features, and operate in
12-V environments even though powered with lowvoltage rails. This document provides recommended
devices and architectures to address current sensing
in this space.
{1.8 V to 5 V}
VS

VBAT
(12 V)

+

OUT



Load

GND

Diagnostic
Control /ADC

Current Sense Amplifier (CSA)

GND

Figure 1. Current Sense Amplifier on 12-V Rail
There are constraints in this space that stem fromconditions such as electrical transient protection
regulations ISO7637-2 and ISO16750-2, jump-starts,
reverse-polarity, and cold-cranking. In general,system-level protection and suppression schemes canbe used to protect downstream circuitry from thesevoltage surge conditions. Types of devices included inthese solutions are smart high-side switches, smart
diodes, or other discrete implementations. These
products may come with internal integrated current
sensing features, but they often are not very accurate(±3% to ±20% maximum error) and have limited
dynamic range.

Dedicated TI current sensors are low in power
consumption and highly accurate (<1% error) inautomotive environments even across temperature.
A matched internal gain network plus input offset
zeroing provides lower measurement drift acrosstemperature compared to either discrete solutions
or ICs with supplemental integrated current sensing.
This amplifier integration and technology can remove
the need for temperature and system calibrations, allat low cost.
Usually, general system protection schemes do not
fully suppress or protect against voltage surges, sothese primary regulations translate into typical voltage
survivability requirements. Depending on the system,
a current sensor may need to survive load dumps,
reverse battery protection, fast load-switching, andinductive kickback voltages. For example, working on
a 12-V battery rail requires at least 40-V survivability
during load dump conditions. It is important to choose
a current sensor that has an input common-mode
voltage (VCM) rating that complies with the worst-case
VCM condition of the system. Otherwise, input voltage
clamping schemes are needed to protect the device
during such conditions.
There are multiple TI Current (Power) Sensing
amplifiers that can operate on a 12-V automotive
battery and survive crucial voltage levels up to 40
V and more. Ultimately, they provide very accurate,
zero-drift, high bandwidth, and low-cost solutions.
Using TI's Product selection tool online, Table 1
tabulates candidates for high-side current sensing
on an automotive 12-V battery rail requiring 40-V
survivability. It should be noted that all devices inTable 1 have multiple gain variants ranging from 20
V/V to 500 V/V.

Table 1. Current Sense Amplifiers for Monitoring 12-V Automotive Battery
TI Current
Sense Amplifier

VCM
Survivability

VOS_MAX(25 °C)BW

Gain Error MAX(25 °C)

IQ_MAX(25 °C)

Features

INA240-Q1-6 V to +90 V±25 µV

400 kHz±0.2%

2.4 mAPWM rejection (very high CMRR), AEC Q100 (temperature grades 1 and0)

INA190-Q1-0.3 V to +42 V±10 µV

45 kHz

±0.3%

65 µA

More accurate version of INA186-Q1. Wide dynamic range.

INA186-Q1-0.3 V to +42 V±50 µV

45 kHz±1%

65 µA

Low input bias current (IB = ±500 pA typical). Wide dynamic range.
Operates with supply voltage (VS) of 1.7 V.

INA180-Q1 (INA181-Q1)-0.3 V to +28 V±500 µV

350 kHz±1%

0.5 mA

Single, dual, and quad channel. Uni- or bi-directional versions

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According to Table 1, the INA240-Q1 provides thebest performance, but is not optimized to monitor a
12-V battery compared to INA186-Q1, which requires
less power, cost, and package size. The INA186Q1 does have high AC CMRR (140 dB) and large
dynamic range (VOUT swings to VS - 40 mV overtemperature). Additionally, the INA186-Q1 possesses
a unique capacitively-coupled input architecture that
increases differential input-resistance by 3 orders ofmagnitude compared to majority of CSAs. High inputimpedance allows the user to filter current noise at
the device input with minimal effect on gain. Using
the data sheet equation if R1 = 1 kΩ, the effective
gain is reduced 43.5 m% for all variants except A1(25 V/V). Figure 2 shows use of INA186-Q1 in battery
monitoring. Filtering at the input (instead of output)means current noise is not amplified and the INA186Q1 can drive a cleaner signal into the ADC without an
output filter loading down the ADC.
VPEAK 42 V
f-3dB =
1/(4R1C)VBAT+RSHUNTLoad

R1 1kVBAT+
RSHUNT

R1 1k

INA186-Q1

Noisy
load



INA186-Q1

GND

GND

Figure 2. INA186-Q1 On 12-V Battery With andWithout Noise Filtering
The breadth of the current sense portfolio enables
the user to optimize tradeoffs when incorporating
common input protection schemes. If the chosen
device states that the Absolute Maximum CommonMode Voltage rating cannot exceed your maximum
expected voltage surge, then it needs input protection.
Along with some passives, the current sensor needs
transient voltage suppression (TVS) or Zener diodes
at the inputs for protection. Figure 3 shows anexample using the cost-optimized current sensor
INA181-Q1.
VPEAK > 28 V

D1

INA181-Q1
R1

VBAT

and the internal ESD structure of the CSA, but it
is usually not needed. If it is needed, R2 should besmall compared to R1. The power rating of diodes
depends on the maximum expected voltage rise, butmore importantly on the turn-on current. The diodecurrent can be reduced by increasing R1 resistance,
but this reduces the effective gain of the circuit and,more critically, increases gain error variation for mostcurrent sensors (except INA186-Q1).
Given the internal resistor gain network and input
differential resistance of the INA181-Q1, an engineer
can calculate the effective circuit gain with R1 using
the equation in the data sheet. Keep in mind that
adding external resistors broaden the system gain
error variance beyond the data sheet limits. This isdue to the fact that INA181-Q1 internal resistors arematched to be ratio metric, but are not trimmed totheir typical values, so their absolute values can varyby ±20%.
Overall, an engineer can choose the INA181-Q1
because total cost with input protection is lower
and increase in gain error variation is acceptable;
however, devices with higher rated VCM are morestraightforward solutions that provide accurate current
sensing over temperature with less complexity andfewer components.
Alternate Device Recommendations
See Table 2 for applications that need either larger
VCM ranges or integrated features such as shunt
resistors or comparators.
Table 2. Alternate Device Recommendations
DeviceOptimized Parameters

Performance
Tradeoff

INA253Integrated 2 mΩ shunt resistor (included in Gain Errorspec). Enhanced PWM rejection

IQ

INA301-Q1

BW and slew rate. Internal comparator with adjustable
threshold and 1 µs alert response time

40 V VCM max

INA302-Q1,
INA303-Q1

BW and slew rate. Dual comparator output withadjustable thresholds and 1 µs alert response time

40 V VCM max

LMP8278QQ1-12 V to +50 V VCM survivability. Adjustable gain andfiltering. Buffered output

VOS

INA1x8-Q1,
INA1x9-Q1≥60 VCM. Current output (adjustable gain). Trimmed
input resistors. Low IB when powered off

VOS

R2 optional+

RSHUNT
R1

R2 optional

Load
D1
GND

Figure 3. INA181-Q1 with Input Protection for VCM> 28 VIn Figure 3, diodes D1 clamp the input VCM of thedevice to less than 28 V, which is the absolute
maximum for INA181-Q1. R2 is optional and canbe included to prevent simultaneous turn-on for D1
24

Related Documentation
1. Transient Robustness for Current Shunt Monitor
2. Measuring Current To Detect Out-of-Range
Conditions
3. Precision current measurements on high-voltage
power-supply rails
4. Integrating the Current Sensing Signal Path
5. Shunt-based Current-Sensing Solutions for BMS
applications in HEVs and EVs

12-V Battery Monitoring in an Automotive Module
Copyright © 2022 Texas Instruments Incorporated

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Application Brief

Simplify Voltage and Current Measurement in Battery Test
Equipment

Kevin Zhang, Maka Luo, Raphael Puzio
Introduction

Function Test

Battery test equipment is used to verify battery packfunctionality and performance prior to shipment to thecustomer. This application brief outlines three major
functional tests that a battery tester performs while
showing how to achieve the desired level of regulated
error.

Functional testing verifies that the battery pack is
operational prior to shipment to the customer. Thisassures that each battery cell and battery pack is
working properly.

Power Grid

...

...

VAC

Single Cell Test Unit

Bidirectional
AC/DC

VDC

Buck / Boost
Converter

Battery
I/V Sensing
0
Amplifier0

DC/DC
Loop Control

Control

AmplifierBattery
I/V Monitor
MCU

ADC

MUX

Figure 1. Traditional Battery Test
Equipment Block Diagram
Formation and Grading of Batteries
After the battery cell or battery pack is assembled,each unit must undergo at least one fully controlled
charge or discharge cycle to initialize the device,
and convert it to a functional power storage device.
Battery vendors also use this process to grade
battery cells, the process of separating the cells
into different performance groups according to target
specifications. For a more in-depth look at the battery
initialization circuit, view our Bi-Directional Battery
Initialization System Power Board Reference Design.
Loop and Feature Test
The loop and feature test refers to cycling the battery
cell or battery pack through repeated charging anddischarging sequences. This verifies that the battery’s
characteristic life and reliability parameters to assure
they are within the specified range of the definedtolerances.

Amplifier Usage in Battery Test Equipment
In typical systems, a Buck converter is usedas the power source for battery charging and a
Boost converter is used for battery discharge. Bothconventional operational amplifiers (Op Amps) andinstrumentation amplifiers (INAs) are used in the
feedback loop to control both the charging anddischarging voltage and current.
To charge the battery, the buck converter is enabled
while the first-stage voltage Op Amps and currentsense INA are used to measure battery voltage andcharging current of the battery cell or battery pack.
The switch between the current-sense Op Amp andthe sense resistor s that the input to the currentsense Op Amp is positive regardless of the directionof current flow across the sense resistor. These
conditioned signals serve as the input to the second
stage error Op Amp for either the voltage loop or
current loop, respectively.
The gained up output from each error Op Amp
serves as the input to the third-stage buffer Op
Amp. The output of the buffer Op Amp feeds into
the feedback pin of the buck converter to control
the output voltage or current. Depending on the
output current requirements, the buck-boost functions
can be accomplished several ways; however, twoapproaches are the most common.
For higher current requirements, an integrated charge
controller and external FET can be used. However,for lower-current requirements, which are common
in cost-sensitive systems, this function can be
implemented discretely as shown in Figure 2. The
design engineer can adjust VV_ref and VI_ref on thepositive input pins of the error Op Amps to adjust
the target output voltage and current of the buckconverter to the optimal value.

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In a typical battery charging application, the output
voltage of the current-loop error Op Amp starts
high, putting the buck converter into constant current
output.
In the next phase, the output voltage of the voltageloop error Op Amp goes high, putting the buckconverter into constant voltage output. When thebattery is being discharged, the boost converter isenabled. The Op Amps control the battery discharge
current and voltage, functioning in the same manneras they do when the battery is being charged. The
boost converter boosts the battery voltage to VDC,
which is usually 12 V.
Other Single
Cell Test Units
Power Grid

Single Cell Test Unit

TPS54335A

Buck
Converter

VAC
Bidirectional
AC/DC

VDC

SN74LV4053

SW
COMP

SwitchTPS6117B
Boost
Converter

VI _ ERR _ RTI  ERRIOUT  I SET  R SENSE
V V _ ERR _ RTI  ERR VOUT  V SET

200 V

21 mV

(1)
(2)

If the desired regulated output voltage is set to VSET
4.2 V, the input error of amplifier will be:
Assuming the temperature rises from 25°C to 85°C
and the battery voltage is 4 V, we can easily calculate
the real world error from one of our low-offset and low
offset drift Op Amps, the TLV07.
INA125(3)

V TLV07 _ ERR _ RTI  VOS _ max  dV OS / dTmax  60 C  4 V / CMRR DC

0

SW
COMP

-

Buffer
Amplifier

Voltage
Loop Error
Amplifier 100 V  0.9 V /  C  60  C  4 V / 158489
 154 V  VI _ ERR _ RTI and V V _ ERR _ RTI

0-

To Monitoring Circuit-+

For example, if the desired regulated output current
target, ISET is 10A, and the current sensing resistor,
RSENSE is 20mΩ, the input error of amplifier will be:



TLV07

TLV07
(Optional)

Since the major errors come from the voltage- andcurrent-sense amplifiers, it’s important to select highprecision amplifiers.

Voltage
Sense
Amplifier
+

+
TLV07
VV_ref to set VOUT
To Monitoring Circuit
Current
Loop Error
AmplifierCurrent
Sense
Amplifier
+

+
TLV07
VV_ref to set IOUT

TLV07
INA188
INA826
INA125Figure 2. Battery Test Equipment
Typical Amplifier Configuration
System and Amplifier Requirements

Using the calculated numbers above, it is clear thata precision Op Amp similar to TLV07 is an ideal Op
Amp to meet the system output current and voltage
error requirements.
For our next example, we use an INA which integrates
all the feedback resistors. delivers VOS_max = 150µV and dVOS/dTmax = 0.5 µV/°C and is a good fit
to perform the current-shunt amplifier function in asystem with a simplified design.
If the system requires even higher performance
specifications, the current and voltage error can bechanged to 0.05% and 0.1%, respectively. In thiscase, precision INAs such as the zero-drift INA188,
can be used. Assuming the same conditions from theabove example, with a 60°C temperature rise and
VBAT of 4 V, the real-world error from the INA188 is:
VI_ERR_RTI= 67 µV and VV_ERR_RTI< = 4.2 mV

Typical system requirements:

Reference Circuit of Amplifier in Each Stage••

Looking at the voltage and current sense reference
circuit shown in Figure 3, I+ and I- contributions are
resultant of the current sense resistors. The B+ and
B- components are from the positive and negative
terminals of the battery. Since the actual battery
voltage might be higher than 5 V, the typical Op Amp
power supply is 12 V. The TLV07, INA188 and INA125
all have 36 V max (±18 V) supply voltage, meetingsystem requirements.

Regulated current error ERRIout = 0.1%
Regulated voltage error ERRVout = 0.5%

To achieve the above requirements, an Op Amp withlow offset voltage (VOS), low VOS temperature drift
and high CMRR, like the TLV07 is needed.
The Op Amps create a closed loop with the powerstage, the voltage on the inverting input of the error
Op Amp will be very close to the reference voltage
VV_ref and VI_ref, thus minimizing the error from thelarge loop gain.
26

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As battery current can be close to zero during
charge and discharge cycles, a bi-polar supply is
implemented in the first stage current-sensing Op
Amp to avoid clipping the current sense signal. TypeIII compensation is applied on each stage of theerror Op Amp , with R12, C3, C4 and R6, C1, C2
respectively. To assure loop stability, these values
should be fine-tuned based on the actual power
supply design.
R9 10 k
B+
B+

VSET

+

R8 20 kR4 50 k+ 12 V+ 12 VR7 20 k–R11 10 k+–

U4 TLV07

R12 1 kU3 TLV07

D2

COMP
Or
BufferC3 100 n

C4 10 pR1 1 kI+

R2 1 kI

R4 50 k+ 12 VISET+

R5 10 k–+–U2 TLV07

R6 1 kU1 TLV07

D1+ 12 V+

C5 10pI
C6 10pR Q2 V+R Q1 V--U1 INA188- 12 V

DeviceSystem Benefits

TLV07(Op Amp)DeviceLow-offset voltage and low-drift provide
sufficient regulated current and voltage error forcost-sensitive systems

Low-offset voltage and zero-drift provide lower
regulated current error and voltage error whilea high CMR (104 dB Min) decreases common
mode interference+ 12 VISET

REF

R3 1 kTable 1. Three Types of Op Amp forBattery Test Equipment

INA188(Instrumentation
amplifier)C1 100 n

C2 10 pI+

Voltage and current sensing are the two mostsignificant measurements in battery test equipment
systems. Furthermore, the most important parametriccharacteristics for this application is a precision Op
Amp or INAs that feature low voltage-offset anddrift. These parameters are critical to assure highperformance sensing while minimizing the first stage
contribution to system error.

High CMR (common mode rejection) of (100 dB
INA125Min) increases dynamic range at the output; low(Instrumentation
offset voltage and low drift reduce the need for
amplifier)costly and time-consuming calibration+5V
R3 50 k+ 12 V

Conclusion

R5 10 k+–U2 TLV07

R6 1 kD1

C1 100 n

C2 10 pUse instrumentation amplifiers forhigher precision requirements

Figure 3. Voltage and Current Sense Circuit with
TLV07 and INA188 in High-end Application

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Application Brief

Current Sensing Applications in Communication
Infrastructure Equipment

In this article, a fresh look is taken into themajor electronic end equipment for cellular wirelessinfrastructure (WI) from the perspective of current
sensing (CS). Several types of CS applications insuch equipment are reviewed.
Current Sensing in Power Supply Block
As shown in Figure 1, the power supply for the
WI equipment comes from the utility grid, solar
energy, or sometimes a combination of the two. The
power supply is often backed up with battery storage
for uninterrupted service during a power outage,
especially in remote areas where solely depending on
grid electricity is not an option due to limitations fromphysical accessibility or economic feasibility.
DCDC Charger

Current Sensing at Point Of Load
The typical WI electronic system is powered from a
DC bus, such as 12 V to 48 V. Lower supply rails arederived from the bus voltage.
These lower voltage rails are called point of load(POL) supplies, stemming from the fact that theysatisfy a set of specific requirements and arenormally located in the vicinity of the loads they
serve. Depending on how critical or informative themeasurements are, sometimes it is desirable tomonitor the current or voltage in one or more of these
POL supplies. The main requirements for the CSA in
this situation may include (among others) accuracy,
speed, dynamic range, and power dissipation by the
associated shunt resistor.
VDD

AC/DC

CSA
High Side I-Sense
Point of Load

Load

CSA
Low Side I-Sense

Figure 1. WI Power Supply Block Diagram
The power supply block can be either integrated
into the WI end equipment, or it can be standalone. Regardless of the implementation, a common
requirement is an intelligent power management
system to charge batteries and ensure seamless
transitions between power sources. Current andvoltage sensing is an indispensable function in such
power management systems.
Current sensing can be implemented either on thehigh side or on the low side. Dedicated high-voltage,
shunt-based, Current Sense Amplifiers (CSA) suchas the INA240 might be needed for fault to ground
prevention. Magnetic current sensors such as the
TMCS1100 or TMCS1101 are both great choicefor high-voltage applications due to their inherent
galvanic isolation.

Figure 2. Point of Load Current Sensing Options
As shown in Figure 2, current can be sensed at eitherside of the load, with analog or digital CSA, andthrough either external or integrated shunt resistor.
CSA comes with a matched resistor gain network thatprovides value in terms of cost, board space, andperformance. Most CSAs feature fixed-gain, ranging
from 10 to 1000. Some CSAs offer configurable
gain. For example, the INA225 has configurable gain
through two digital control pins, while other CSAs
have a gain that is configurable through an external
resistor, such as INA139.
System integration is further improved when a CSA
is chosen that comes with integrated analog to digitalconversion (ADC) and a shunt resistor.

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The key considerations in selecting a CSA andassociated shunt resistor for POL measurement starts
with common-mode voltage, current range, accuracy,
and speed. In addition, if overcurrent protection (OCP)
is required, a CSA with an integrated fast-action
comparator is often an ideal choice, where systemparameters such as offset and propagation delay
are specified. Compared with discrete components,
such a CSA helps remove uncertainties and therefore
simplifies the design.
To monitor multiple POLs, a multi-channel CSA likethe INA2290 or INA4180 might make sense, as
it offers four channels of analog output. When amicrocontroller or FPGA is present in the equipment,
an ADC channel is normally available, as well as adigital bus such as I2C. In this situation, either ananalog or digital output CSA may be implemented
as a POL monitor. A multi-channel digital monitor
such as the INA3221 is another option that frees up
controller ADC channels while taking advantage ofan existing I2C bus. This device offers a number of
warning and alert signals for fast action in case of a
fault, as well as current, voltage, or power informationof three independent channels.
Current Sensing in Power Amplifiers
The bias current in power amplifiers (PA) is adjusted
to suit the need of an end application, modulation
scheme, and operation class. A typical PA withcurrent sensing is shown in Figure 3.
The PA is often constructed with silicon LDMOSor GaN technology. Current sensing is important in
PA applications, both from the standpoint of the PA
operation and from the standpoint of overall energy
efficiency management. Under the same bias voltage,
the PA bias current differs due to device variation.
Further, the bias current changes with temperature.
Consequently, in order for the PA controller toaccurately control the bias current, both the current
and temperature information must be available. The
bias current information is necessary in improving
system efficiency, where around 50% of total system
power is consumed by the PA itself.
Integrated power amplifier monitor and control
systems, such as the AMC7836, can simplify PA
circuit design. As mentioned, due to natural device
variation, knowing gate voltage alone is sometimes
not sufficient in order to achieve accurate bias current
control. When current sensing is required in thecontrol loop, a separate high-voltage CSA, such as
the INA290, can be used.

29

Power amplifier monitor and control systems suchas the AMC7834 are another option with integrated
current sensing capability. Such a solution offers thepossibility of further reducing board space.
VDD

Current/Voltage/Power/
Energy Sense
ADC

Temperature Sense

PA Controller(w/uC or FPGA)

DAC

d
g
s
RF Input

Figure 3. PA Biasing and Current Sensing
Alternate Device Recommendations
TI offers a complete line of CSA and magnetic
sensors that serve well in WI end equipment, fromhigh-voltage supply current and PA current sensing
to general purpose POL current monitoring. The
high-voltage INA202 also comes with integrated
comparator and reference output to facilitate the
OCP requirement. For applications where superior
accuracy is required, the INA190 family of devices
are good choices with nA input bias current.
These devices are essential in situations where
the sensed current is very small. Some of thesedevices come with Enable pins for further power
reduction; some are offered in a WCSP package forboard space optimization. For applications with lower
common mode voltage requirements, the INA180
offers excellent speed and overall performance value.
The INA301 family of devices features integrated fastcomparators and high-speed amplifiers. Both outputs
are available that suit the need of OCP.
Table 1. Alternate Device Recommendations
DeviceCharacteristics

INA202

Common mode range -16 V to 80 V;
Comparator

INA180Low IQ; High bandwidth

INA190Low IQ; Low IB; Enable pin

INA301High bandwidth amplifier; Fast comparator

Related Documentation
1. Hybrid Battery Charger With Load Control for
Telecom Equipment
2. Precision Current Measurements on High-Voltage
Power Supply Rails
3. Common Uses for Multi-Channel Current
Monitoring

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Application Brief

Safety and Protection for Discrete Digital Outputs in a
PLC System Using Current Sense Amplifiers

A Programmable Logic Controller (PLC) is themost widely accepted computer protocol in industrial
control systems for factory automation application.
PLC system is a controller that controls, prioritizes,
and provides status of the system. The controller
is programmed via basic binary logic much like amodern computer. The PLC system consists of:
1. PLC computer processor
2. The power supply rack
3. Back plane for power
4. Digital input and output module
5. Analog input and output module
6. Computer software
7. A network interface for remote connectivity
PLC systems are widely used in industrial applications
that is accelerating industrial 4.0 revolution.
PLC systems are enabling faster integration ofsemiconductor devices for control and automation toincrease efficiency and improve factory throughput.
Industrial automation and integration examples
include controlling of temperature, turning on and off
a light fault indication, weighing of a package usingpressure sensors, turning on and off a solenoid relay.
As industrial systems can be noisy environmentswith high-frequency signals and noise coupling
into low-voltage signals, the PLC system's output
modules are optocoupled. Its robustness to noise,
simple architecture, ease of programming language,
industrial certifications, and safety features are thereasons PLC systems are the most widely usedindustrial protocol.
PLC System Block Diagram
The inputs and outputs of the PLC system arecategorized as digital or analog as illustrated in
Figure 1. The digital inputs provide an ON-OFF status
to the control circuitry. Some examples of digital
input devices include limit switches, photoelectric
sensor, proximity, and pressure sensor. Analog input
devices such as thermocouples, tachometers, andforce sensors provide variable output responses.

PLC digital outputs are used to turn ON-OFF thestarter to engage a motor, to turn on a lamp to
indicate a fault, or to control the solenoid that engages
relay. The analog outputs include current level output
and resistance level that can be used to control andmonitor heaters or control the speed of a motor.
Input

Output24V

24V
Solenoid Relay(digital output)

Push Button(digital input)
24V

24V

Programmable
Logic
Controller(PLC)

Thermocouple(analog input)
24V

Lamp
(digital output)

Pressure Sensor(analog input)

Figure 1. PLC System Block Diagram
Discrete PLC Digital Outputs Safety
Figure 2 illustrates a description of a PLC digital
output circuit. PLC digital outputs are designed withhigh-drive strength capability that can be as high as
1 A. The digital outputs can be connected to drivea solenoid relay to take control of an action initiatedby the PLC controller. Discrete current sensors
connected in series with the load, as shown in Figure
2, monitor current flowing to the load continuously
and report the presence of excessive currents to thecontroller to take an action. As PLC digital outputs canswing from –0.7 V to 24 V, a high-side current sense
amplifier with low-offset and low-gain error enables
safety for high-output drives.
Current
Sense
Amplifier
OptoCoupler

Load

Current Flow

PLC digital Output+24V

GroundFigure 2. PLC Digital Output Sinking
Current Circuit

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As the PLC digital output drive can be high, thesinking current capability is one of the key safetyparameters. The outputs are designed with NPN
transistors with a built in diodes for over voltage
protection. The system ensures that when the PLC
digital outputs are engaged the sinking current fromthe power supply is always within the PLC's specified,over temperature operating range. A discrete current
sense amplifier can protect the digital outputs from an
overcurrent condition, provide diagnostics to address
faulty load conditions and address preventive action
for premature system failure.
High-Current PLC Digital Outputs Safety
PLC digital outputs can be directly tied to high-current
solenoid drivers or high-current LED lamps to close
relays or to indicate a fault in a factory automation
application. If the current output drive is higher than
the PLC system is rated for, a discrete FET canbe used to control the current flow form the 24-V
supply to the load. Figure 3 illustrates the connectionof a PLC digital output to an external low RDS on
FET to further increase the output drive strength.
One disadvantage of this approach is the reliabilityof the external FET. Using a current-sensing amplifier
to monitor the load current can ensure that the PLC
system is operating safely.
Current
Sense
Amplifier
OptoCoupler

Alternate Device Recommendations
The INA293 is another device to recommend for thisapplication. The INA293 is a unidirectional current
sense amplifier that can support a common-mode
voltage from –4 V to 110 V and can survive –20 V to116 V. This large negative common-mode survivability
is important due to inductive kickbacks seen whenengaging the solenoid or a motor starter. The INA293
also has a high-bandwidth of 1MHz which enables
fast reaction times in the event of an overcurrent
scenario.
The INA290 is also another device that can be usedin PLC systems. INA290 is designed to operate witha common-mode voltage range from 2.7 V to 110 V.
Although this is a high-side sense device, the INA290
can survive common-mode transients of –20 V to 120
V.
Table 1. Alternate Device Recommendations
DeviceOptimized Parameter

Performance TradeOff

INA293

Bandwidth : 1.3 MHz,VCM: –4 V to 110 V,
Offset voltage: 15 µV,
Gain error: 0.15%

N/A

INA281

Bandwidth : 1.3 MHz,VCM: –4 V to 110 V,
Cost Optimized

Offset voltage: 55 µV,
gain error: 0.5

INA290

Bandwidth: 1.1 MHz,
Offset voltage: 12 µV,
Gain error: 0.1%,
Package: SC-70

High-side only (VCM: -4
to 110V)

INA280

Bandwidth: 1.1 MHz,
Package: SC-70,
Cost Optimized

Offset Voltage: 150 μV,
Gain error: 0.5%

Load

+24V

Current Flow

PLC digital Output

The signal throughput bandwidth of INA240 is 400
kHz at the gain 20. The high bandwidth and highslew rate (2V/µs) enables the amplifier to be used for
detecting fast over current or shorted load conditions
provided the sampling ADC within the PLC system isfast enough to sample currents.

GroundFigure 3. PLC Discrete Digital Output Control
INA240 is a high-precision, bidirectional current
sense amplifier with low-input offset and gain drift
across temperature range designed for measuring
currents on discrete PLC digital outputs. The INA240
is specifically designed to work in switched nodeenvironments where the common-mode transients will
have large dv/dt signals. The ability to reject highdv/dt signals enables accurate current measurements
to ensure necessary protection and meet the required
safety standards. The INA240 has low maximum
input offset voltage of 25 µV and a maximum gain
error of 0.2% allowing for smaller shunt resistancevalues to be used without sacrificing measurement
accuracy. The offset drift and gain error drift is as low
as 0.25µV/°C and 2.5ppm/°C respectively enabling
accurate and stable current measurements acrosstemperature.
31

Related Documentation
1. Current Sensing in an H-Bridge
2. Switching Power Supply Current Measurements
3. High-Side Drive, High-Side Solenoid Monitor WithPWM Rejection
4. Measuring Current To Detect Out-of-Range
Conditions

Safety and Protection for Discrete Digital Outputs in a PLC System Using
SBOA193B – DECEMBER 2020 – REVISED MARCH 2022
Current Sense Amplifiers
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Analog Design Journal

Signal Chain

Current sensing in high-power USB Type-C®
applications
By Ben Damkroger

Product Marketing Engineer, Sensing-CSPS

Introduction®

operation. For sink devices, due to lower manufacturingcosts of power adapters and corners cut during construction as a result, there is no guarantee that consumers will
use power adapters with sufficient protection. Sometimes
faulty power adapters may provide the 20 V before USB
negotiation, which might overload sink devices. For source
devices, cheap USB cables and USB-C PD devices may
have faulty wiring, causing a short on the load side of acharger and ultimately requiring some protection.
When designing devices that act as power sources, suchas docking stations or chargers, shield devices are
required downstream, especially when running near the
100-W limit of USB PD. Integrated current sensing in USB
PD controllers is usually only ±10% to ±15% accurate.
These accuracy levels may be sufficient for some, but amore accurate solution for overcurrent protection maximizes the amount of current that the USB port can
provide while staying below a fixed power level.
For example, to account for current tolerance in a
20-V/5-A (100-W) system, the maximum current limit
should be set 10% away from 5 A at 4.545 A (5 A × 1 ÷ 1.1).
With a maximum current of 4.545 A, the maximum possible
power delivered to a load device is 90.9 W. Additionally,
when the current is 10% below the maximum current at
4.090 A, a system would only deliver 81.8 W of power.

®

The introduction of USB Type-C, also designated USB-C,
connectors eliminated the frustration of flipping USB
cables three and four times before finding the correctorientation to plug in a device. A smaller, reversible cable
is not the only thing new with the evolution of USB technology, however; the standard also enables the replacement of various electrical connectors including USB-B and
USB-A, HDMI, DisplayPort, and 3.5-mm audio cables.
Sadly, USB-C alone still has a power limit of only 15 W.
However, USB Power Delivery (USB PD) increased thatpower limit to 100 W through the introduction of configurable voltage levels of 5 V, 9 V, 15 V or 20 V. This 100-W
limit means that higher-power devices such as laptops,
tablets and monitors can all charge and operate using asingle USB PD cable.
This increased power has more design considerations
than previous standards, however. USB-C cables have
24 pins, including four Vbus wires and four ground wires,
more than USB 3.0. These Vbus lines require overvoltage,
overcurrent and reverse-current protection. Protections
should be implemented that detect transient spikes
caused by faults in the Vbus line or faults internal to aload device. These protections should be added in both
source and sink (load) devices to guarantee safe
Figure 1. USB PD power range

2.5 W

4.5 W

USB Type-C®
USB 2.0
USB 3.0

Texas Instruments

65 W

7.5 W 15 W 25 W

100 W

USB Type-C® and USB PD
USB BC 1.2

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Analog Design Journal

Signal Chain

To set a higher current threshold, a discrete currentsense amplifier like the INA199, with its 150-µV voltage
offset and 1% gain error, can easily provide 1.5% accuracy
when the current is greater than 1 A in a 100-W application. This device enables the current limit to be set at
4.926 A (5 A × 1 ÷ 1.015), which in turn means that theUSB port could deliver 98.52 W to the load. Figure 2
shows the root-sum-square (RSS) error curves for the
INA199 and INA381.

In the most straightforward implementation, the analog
output of the comparator could be used to trip the FET.
Or digital logic could be used with an analog-to-digitalconverter (ADC) and microcontroller (MCU) to decide
when to switch the FET off. These overcurrent protection
schemes provide a response time that is much faster thana thermal fuse and can be reset and reused without
replacement. The INA381 current-sense amplifier, with its
fast integrated comparator, shrinks the bill of materials by
eliminating the need for a comparator and makes thedesign process more straightforward. Figure 3 is a simplified circuit using this device.

Figure 2. INA199 and INA381
total measurement error
5.5

4.5
4

R Shunt

3.5

INA381

ALERT

3
2.5

+

2

V Bus
–

RSS Error (%)

Figure 3. Simplified e-fusecircuit using the INA381

INA381A2 Voltage = 20 V
INA381A2 Voltage = 5 V
INA199B1 Voltage = 20 V
INA199B1 Voltage = 5 V

5

1.5
1

2

2.5

3

3.5
4
4.5
Current (A)

5

5.56

Z LoadFor devices that sink power over a USB PD supply, it isstrongly suggested to include current sensing to protectfrom internal faults. It is impossible to know whether
consumers will power peripheral devices with USB PD
controllers that have adequate overcurrent protection.
One easy solution is to design internal overcurrent protection in the device’s Vbus input by wiring a discrete
current-sense amplifier, a comparator and a field-effecttransistor (FET) as an e-fuse. With an e-fuse, the currentsense amplifier detects whether the current is too highand the comparator controls the FET triggers that turn off
the FET and interrupts the current.

Texas Instruments

Selecting the correct current sensor is essential, especially given their variety. Digital power monitors, forexample, provide an integrated ADC that frees up space
on a system’s MCU analog inputs, while also giving accessto extra features like power calculation and accumulation(energy). Analog current-sense amplifiers, on the other
hand, are more popular because of their low cost andversatility. The integrated gain resistors and input stagesof analog current-sense amplifiers enable their inputs todetect common-mode voltages beyond their supply, thus
making these devices better for current sensing than standard operational amplifiers. Current-sense amplifiers canalso come integrated with comparators for faster response
times and alert signals for overcurrent protection; the latteris especially important for protecting USB-C PD devices.

33

ADJ 1Q 2021

Analog Design Journal

Total Error =Signal Chain
(1)

2
Vos
+ CMRR 2 + PSRR 2 + Gain Error 2 + Shunt Tolerance2 + BiasCurrent 2

As previously mentioned, current-sense amplifiers are
more accurate than the integrated current sensing of most
USB-C PD controllers. To understand why, first consider
the various error sources found on current-sensing data
sheets and use these sources to calculate errors using theroot-sum-square (RSS) method. The different error
sources present in current-sensing amplifiers are shown
by Equation 1 above.
The input offset voltage (VOS) is the dominant source oferror when measuring small currents because it is larger
in relation to the relatively small shunt voltage—it diminishes as the shunt voltage increases at higher currents.
This offset error is inherent to all amplifiers and is a resultof resistor and transistor mismatching. Gain error dominates the error at larger currents, as it remains present
even at high currents, and does not diminish as the shunt
voltage increases. These error sources can be manuallycalculated using Equation 1. For additional information,
consult the References and Related Web sites on thispage.

References
1. TI Precision Labs – Current Sense Amplifiers, Texas
Instruments training and videos
2. Maximize your system with current sense amplifiers,
Overview, Texas Instruments products and reference
designs

Related Web sites
Product information:
INA199
INA381
INA381 Design tools and simulation

Conclusion
With the advent of USB PD, the number of high-power
USB devices continues to grow. This article presented theoptions available to implement current protections andpower monitoring, and also compensate for tolerance
errors that are typically encountered with integrated
current sensing in USB PD controllers. The need to maximize power to a load in a power-source device or protect a
power-sink device is also highlighted. Current-sensing
amplifiers provide an easy solution to many of these
design challenges, with higher accuracy and greater design
flexibility.

Texas Instruments

4
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Application Brief

Low-Drift, Precision, In-Line Motor Current Measurements
With PWM Rejection

Scott Hill

Current Sensing Products

The demand for higher efficiency systems continues
to increase, leading to direct pressure for
improvement in motor operating efficiency andcontrol. This focus applies to nearly all classes ofelectric motors including those used in white goods,
industrial drives and in automotive applications. The
operational characteristics of the motor fed back into
the control algorithm are critical to ensure the motor
is operating at its peak efficiency. Phase current is
one of these critical diagnostic feedback elements
used by the system controller enabling optimum motor
performance.

voltage steps. Because real-world amplifiers do nothave infinite common-mode rejection potentially large,
unwanted disturbances appear at the amplifier output
corresponding to each input voltage step as shownin Figure 2. These output disturbances, or glitches,
can be very large and take significant time tosettle following the input transition depending on thecharacteristics of the amplifier.

Due to the continuity of the measurement signal
and direct correlation to the phase currents, an ideal
location to measure the motor current is directly in-linewith each phase as shown in Figure 1. Measuring
current in other locations, such as the low-side ofeach phase, requires recombination and processing
before meaningful data can be utilized by the control
algorithm.
Figure 2. Typical Output Glitch From Large Input
VCM Step

Figure 1. In-Line Current Sensing
The drive circuitry for the motor generates pulse
width modulated (PWM) signals to control the
motor’s operation. These modulated signal subject
the measurement circuitry placed in-line with each
motor phase to common-mode voltage transitions
that can switch between large voltage levels oververy short time periods. An ideal amplifier would
have the ability to completely reject the commonmode voltage component of the measurement andonly amplifier the differential voltage corresponding
to the current flowing through the shunt resistor.
Unfortunately, real-world amplifiers are not ideal
and are influenced by the large PWM-driven input

A common approach to this measurement is to selecta current sense amplifier with a wide bandwidth. Inorder to stay above the audible frequency range,
modulation frequencies ranging from 20kHz to 30kHz
are typically selected. Amplifier selection for making
in-line current measurements in these PWM-driven
applications targets amplifiers with signal bandwidths
in the 200kHz to 500kHz range. The selection of theamplifier was not historically based on actual signal
bandwidth which are significantly lower than the PWM
signal. The higher amplifier bandwidths were selected
to allow the output glitch to settle quickly following an
input voltage transition.
The INA240 is a high common-mode, bi-directional
current sense amplifier designed specifically forthese types of PWM-driven applications. This device
approaches the problem of measuring a small
differential voltage in the presence of large commonmode voltage steps using integrated enhanced PWM
rejection circuitry to significantly reduce the output
disturbance and settle quickly. Standard current sense

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amplifiers rely on a high signal bandwidth to allow
the output to recover quickly following the step,
while the INA240 features a fast current sense
amplifier with internal PWM rejection circuitry toachieve an improved output response with reduced
output disturbance. Figure 3 illustrates the improved
response of the INA240 output due to this internal
enhanced PWM rejection feature.

Figure 3. Reduced Output Glitch By Enhanced
PWM Rejection
For many three-phase applications there are few
requirements on the accuracy of this in-line current
measurement. Limited output glitch is necessary to
prevent false over-current indications in addition tohaving an output that quickly responds to ensuresufficient control of the compensation loop. For
other systems, such as electronic power steering(EPS), precise current measurements are needed toprovide the required feedback control to the torqueassist system. The primary objectives in an EPS
system are to assist with additional torque to thedriver’s applied torque on the steering wheel andprovide a representative feel in the steering response
corresponding to the driving conditions. Phase tophase current measurement errors can become very
noticeable in this tightly controlled system. Any
unaccounted for variance between phases leads
directly to increased torque ripple that is perceptible
to the driver through the steering wheel. Reducing
the measurement errors, especially those induced
by temperature, is critical to maintain the accurate
feedback control and to deliver a seamless user
experience.

36

Common system-level calibration frequently reduces
the reliance on an amplifier's performance atroom temperature to provide precise measurement
accuracy. However, accounting for parameter shifts
such as input offset voltage and gain error as theoperating temperature varies is more challenging.
Good temperature compensation schemes are basedon characterization of the amplifier’s performancevariation over temperature and rely on consistentand repeatable response to external conditions fromsystem to system. Improving the capability of theamplifier to remain stable with minimal temperatureinduced shifts is ideal to reduce the need for complex
compensation methods.
The INA240 features a 25µV maximum input
offset voltage and a 0.20% maximum gain
error specification at room temperature. More
importantly for applications requiring temperaturestable measurements, the device's input offset voltage
drift is 250nV/°C with a 2.5ppm/°C amplifier gain drift.
Even as the operating temperature varies over thesystem’s entire temperature range, the measurement
accuracy remains consistent.
The INA253 features all of the performance benefitsof INA240 amplifier with the inclusion of integrated
shunt. The integrated shunt is a low inductive,
precision, 2mΩ 0.1% with a temperature drift of<15ppm/°C. The INA253 is the most accurate current
sense amplifier that eliminates the error introduced
due to shunt and parasitic introduced due to thelayout.
Combining the measurement temperature stability,
wide dynamic input range, and most importantly
enhanced PWM input rejection, the INA240 is an ideal
choice for PWM-driven applications requiring accurate
and reliable measurements for precisely controlled
performance.

Low-Drift, Precision, In-Line Motor Current Measurements With PWM
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Alternate Device Recommendations

Table 1. Alternate Device Recommendations

Depending on the necessary system requirements,
there may be additional devices that provide theneeded performance and functionality. The INA282 isable to measure very precisely large common-mode
voltages that do not change as quickly as whattypically is seen in PWM driven applications making it
ideal for high voltage DC applications. The LMP8481
is a bi-directional current sense amplifier used forhigh common-mode voltages that do not require theamplifier to include ground within the input voltage
range.

DeviceOptimized Parameter

Performance Trade-Off

INA282

Common-Mode Input
Range: -14V to +80V;
MSOP-8 Package

Low Bandwidth, Ideal For
DC Applications

LMP8481

Low Power: 155uA;
MSOP-8 Package

Common-Mode Input
Range: 4.5V to 76V;
Lower Accuracy

Table 2. Related TI Application Briefs
SBOA202

Benefits of a Low Inductive Shunt for
Current Sensing in PWM Applications

SBOA189

Precision Brightness and Color Mixing in
LED Lighting Using Discrete Current Sense
Amplifiers

SBOA161

Low-Drift, Low-Side Current Measurements
for Three-Phase Systems

SBOA163

High-Side Motor Current Monitoring forOver-Current Protection

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TI Tech Note

Tech Note

High-Side Drive, High-Side Solenoid Monitor With PWM
Rejection

Arjun Prakash,Current Sensing Products
A solenoid is an electromechanical device that is
made up of a coil wound around a movable ironmaterial, also called an armature or plunger. When an
electric current is passed through the coil, a magnetic
field is generated, causing the armature to travel overa fixed range. Figure 1 shows an illustration of anelectromechanical solenoid. Solenoids are often
designed for simple ON - OFF applications like relays
that require only two states of operation. Thesesolenoids can be also be designed for linear operation
where the current is proportional to the position of thearmature. Linear solenoids are used in several
applications where pressure, fluid, or air is precisely
regulated. In automotive applications, linear solenoids
are used in fuel injectors, transmission, hydraulicsuspension, and for haptic effects. Linear solenoids
are seen in critical medical applications that requireprecise air flow control as well as industrial
applications that redirect and control fluid flow.
Induced Magnetic Field Inside Coil
Rod Moves In

S

NCurrent

Induced Magnetic Field Inside Coil
Rod Moves Out

S

N

Current

Figure 1. Electromechanical Solenoid
Construction
There are multiple configurations for connecting anddriving solenoids. One common approach to driving
solenoids is to use a high-side driver configuration. In
this configuration, the current sense amplifier isconnected between high-side switch and the solenoid
as shown in Figure 2. One benefit to this configurationis the solenoid is isolated from the battery voltage

when the high-side switch is turned off. Eliminating
the solenoid's continuous connection to the battery
voltage reduces solenoid degradation and early
lifetime failures.
Battery
Reference
Voltage+
INA253Figure 2. High-Side Drive With High-Side Current
Sense
The current sense amplifier shown in Figure 2 must
be able to reject high common-mode dv/dt signals aswell as support common-mode voltages that fall below
ground. In the above configuration when the high-side
switch is turned on, the solenoid is energized by thecurrent flowing from the battery. The duty cycle of thehigh-side switch determines the current flowing
through the solenoid, which in turn controls the travel
range of the plunger. At the time when the high-side
switch is turned off, the current flows through theflyback diode forcing the common voltage to drop one
diode drop below ground.
Solenoids and valves are highly inductive in nature.
The effective impedance of solenoid can be simplified
as resistance and inductance. The coil is constructedusing copper (4000ppm/°C) and the effective
resistance varies on the type of solenoids from 1 Ω for
haptic applications to 10 Ω for a linear or positional
valve systems. The inductance for all of the solenoids
ranges from 1 mH to 10 mH. Figure 3 shows example
of current profile of a solenoid driver in open-loop
mode at 25 °C and 125 °C. Over a 100 °C rise inambient temperature without compensating for Cu
resistance, the plunger travel distance accuracy isaround 40%. The solenoid current flow directly
controls the plunger's travel distance. If the ambient

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TI Tech Notetemperature changes, the plunger's travel distancechanges impacting the output control which could be
regulating pressure, fluid, or air.
PWM
Current @ 25C
Current @ 125C

0V
-0.7V

Figure 3. Solenoid Current Profile AcrossTemperature
Measuring current in solenoid and valve applications
provides the capability to detect changes in asolenoid's operating characteristics. Current
measurement can identify the effects of a decrease in
the magnetic field of an aging solenoid to detect faulty
components before they fail. In an open-loop solenoid
control system, the variation of effective impedance
can drift 40% for a 100 °C rise in temperature from thecopper windings. Current measurement used in acurrent control feedback loop can reduce thesolenoid's impedance variation over temperature from
40% down to 0.2% using the INA253 current sense
amplifier.
The INA253 is a high-side, bidirectional current sense
amplifier with an integrated 2-mΩ low inductive shuntthat can support large common-mode voltages
ranging from –4 V to +80 V. The integrated shunt isfactory calibrated to provide <0.1% total systemaccuracy with a gain error temperature drift of<15ppm/°C. The INA253 is specifically designed tooperate within PWM applications where high dv/dt
transients needs to be suppressed. INA253 is
designed with circuitry to suppress dv/dt signals. Thisfeatures lowers blanking time enabling accurate PWM
current measurements at lower duty cycle. The
device's low offset voltage, drift, gain, and highbandwidth of 400 kHz enables accurate in-line current
measurements for PWM applications. Valveapplications requiring precision control of fluid, air,and pressure all benefit from the accuracy andtemperature stability in the current measurement byusing the INA253. The integrated precision shunt of
the INA253 can provide a high-accuracy position
control of <0.2% across temperature, eliminating theneed for current measurement calibration acrosstemperature.

Alternate Device Recommendations
The INA240 is a high-side, bidirectional current sense
amplifier that can support large common-mode
voltages ranging from –4 V to +80 V. The INA240 is
specifically designed to operate within PWM
applications where high dv/dt transients needs to be
suppressed. The device's low offset voltage of 25 µV(maximum), drift of 250nV/°C (maximum), gain (0.2%)
and high bandwidth of 400 kHz enables accurate inline current measurements for PWM applications.
The INA293 is another device to recommend for thisapplication. The INA293 is a unidirectional current
sense amplifier that can support a common mode
voltage from -4 V to 110 V and can survive -20 V to
120 V. This large negative common-mode survivability
is important due to inductive kickbacks seen whenengaging the solenoid. The INA293 also has a highbandwidth of 1 MHz which enables fast reaction times
in the event of an overcurrent scenario. Furthermore,
the INA293 is an high-precision current sense
amplifier with a low offset voltage of 15 µV and gain
error of 0.15%.
The INA281 is another device to recommend, which isa unidirectional current sense amplifier similar. It can
support a common-mode voltage from -4 V to 110 V
and also survive -20 V to 120 V. The INA281 has ahigh bandwidth of 1 MHz for fast in-line
measurements.
Table 1. Alternate Device Recommendations
DEVICE

OPTIMIZEDPARAMETERPERFORMANCETRADE-OFF

INA240PWM settling time: 2µs,
Vos: 25 µV

Package: TSSOPINA293

Vcm range: -4 V to+110 V,
Bandwidth: 1.3 MHz,
Offset voltage: 15 µV,
Gain error: 0.15%

No enhanced PWM
rejection

INA281

Vcm range: -4 V to+110 V,
Bandwidth: 1.3 MHz,
Cost Optimized

No enhanced PWM
rejected,
Offset voltage: 50 µV,
Gain error: 0.5%

Table 2. Related TI TechNotes
DOCUMENTTITLE

SBOA189

Precision Brightness and Color Mixing in
LED Lighting Using Discrete Current Sense
Amplifiers

SBOA161

Low-Drift, Low-Side Current Measurements
for ThreePhase Systems

SBOA163

High-Side Motor Current Monitoring forOver-Current Protection

SBOA193

39

Safety and Protection for Discrete Digital
Outputs in a PLC System Using Current
Sense Amplifiers

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Application Brief

Current Mode Control in Switching Power Supplies

Most switching power supplies are designed withclosed-loop feedback circuitry to provide stable
power under various transient and load conditions.
The feedback methodology options fall into twogeneral categories, voltage mode control (VMC) andcurrent mode control (CMC). Both methodologies
have their strengths and weakness that determine
the appropriate selection for the end-equipment
application.
Control Methodologies
Voltage mode control utilizes a scaled valueof the output voltage as the feedback signal.
This methodology provides simple, straight–forward
feedback architecture for the control path. However,this method has several disadvantages that should
be noted. The most significant disadvantage is output
voltage regulation requires sensing a change in output
voltage and propagation through the entire feedback
signal and filter before the output is appropriately
compensated. This can generate a unacceptably
slow response for systems that desire high levels of
regulation. The feedback compensation of the supply
requires a higher level of analysis to address thetwo poles introduced by the output low–pass filter.
Additionally, the feedback component values must
be adjusted since different input voltages affect theoverall loop gain.
Current mode control addresses the above shortfalls of voltage mode control by using the inductor
current waveform for control. This signal is included
with the output voltage feedback loop as a second,
fast response control loop. The additional feedback
loop does potentially increase the circuit/feedback
complexity, so the advantages need to be evaluatedas part of the design requirements.

2. The power supply looks like a voltage controlledcurrent source. This permits a modular supply
design to allow load sharing between multiple
supplies in a parallel configuration.
3. The effects of the inductor in the control loop
can be minimized since the current feedback loop
effectively reduces the compensation to a single
pole requirement.
While current mode control addresses some of the
drawbacks of VMC, it introduces challenges thatcan effect the circuit performance. The addition of
the current feedback loop increases the complexityof the control/feedback circuit and circuit analysis.
Stability across the entire range of duty cycles andsensitivity to noise signals are other items that need
to be considered in the selection of current mode
control. CMC can further be broken down into several
different types of control schemes: peak, valley,emulated, hysteretic, and average CMC. The below
text discusses the two most common methodologies
used in circuit design — peak and average current
mode control.
Peak Current Mode Control
Peak current mode control (PCMC) utilizes the current
waveform directly as the ramp waveform into the
PWM–generation comparator instead of a externallygenerated sawtooth– or triangle–signal like VMC. The
up-slope portion of the inductor current or high–side
transistor current waveform is used to provide afast response control loop in addition to the existing
voltage control loop. As shown in Figure 1, the current
signal is compared with the output of the voltage error
amplifier to generate the PWM control signal for the
power supply.
VIN

INA240+Control and Gate Drive

VOUT

L
C


+
PWM Generation

+

By using the inductor current as part of the feedback
control:
1. The added current feedback loop responds fastercompared with only using the output voltage for
feedback control. Additionally, with the inductor
current information, the circuit can be designed
to provide pulse by pulse current limiting allowing
rapid detection and control for current limitingneeds.

RSENSE

Reference Voltage

Voltage Error Amplifier

Figure 1. Block Diagram of PCMC circuit

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Current Mode Control in Switching Power Supplies
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Switching power supplies provide high levels of
efficiency between the input and output power rails.
To maintain the high efficiency of the converter, ideallythe sense resistor used to measure the inductor
current is as small as possible to reduce power
loss due to the measurement. This small–valued
resistor results in a small amplitude feedback signal.
Since the inductor current waveform is used directlyas the comparator input signal, PCMC is known
to be susceptible to noise and voltage transients.
Using a current sense amplifier like the INA240
with high common-mode rejection ratio (CMRR)
provides suppression of transients associated withpulse-width modulation (PWM) signals and systems.
The gain flexibility of the INA240 allows the inductor
current waveform be amplified to provide a larger
signal for comparison without the need for additional
gain or sacrificing performance. Additionally, the low
offset and gain errors provide a reduction in design
variations and changes across temperature. To utilize
PCMC, the inductor current necessitates a highcommon–mode voltage measurement. The INA240
common–mode range allows for a wide range insupply input and output voltages.
It should be noted that PCMC most often adds slope
compensation to address stability issues with duty
cycles greater than 50%. The slope compensation isadded to the inductor current before being used as
the comparator input signal.

INA240 high accuracy and low drift specifications
provide consistent measurement across temperatureand different assemblies.
The INA240 provides performance and features
for measurement accuracy which is needed tomaintain good control signal integrity. The INA240
features a 25μV maximum input offset voltage
and a 0.20% maximum gain error specification atroom temperature. Temperature stability is important
to maintain system performance and the INA240
provides input offset voltage drift of 250nV/°C with a
2.5ppm/°C amplifier gain drift. The INA240 featuresenhanced PWM rejection to improve performancewith large common-mode transients and a wide
common-mode input range for maximum design
variance for supply output voltages.
Alternative Device Recommendations
Based on system requirements, alternative devices
are available that can provide the needed
performance and functionality. The LMP8601 family
provides lower performance levels than the INA240
for in-line sensing applications. The INA282
allows current measurement for high common-mode
voltages, making it ideal for high voltage DC
application that do not have PWM signals. The
INA290 is a high-voltage current sense amplifier withhigh bandwidth packaged in a small SC-70 package.
Table 1. Alternative Device Recommendations

VIN

RSENSE
Control and Gate Drive

DeviceOptimized Parameters

Performance Trade-Off

INA253Integrated Low inductive
precision shunt: 2mΩ,
0.1%, Enhanced PWM
rejection+/-15A maximum
continuous current at TA= 85°CINA282

Low power, High Gain
Options, High Supply
Voltage

No Enhanced PWM
Rejection, Higher drift
specifications

INA290Wide Common–Mode
Input Range, Highbandwidth, Small SC-70
package

No Enhanced PWM
Rejection, Unidirectional,
Common–mode range
does not include ground

VOUT

L
C



+

Current Error Amplifier

INA240



+

+

+


PWM Generation

Reference Voltage

Voltage Error Amplifier

Figure 2. Block Diagram of ACMC circuit
Average Current Mode Control
Average current mode control (ACMC) utilizes theinductor current waveform and an additional gain
and integration stage before the signal is compared
to a externally provided ramp waveform (similar to
VMC). This allows improved immunity to noise andremoves the need for slope compensation. Figure 2
shows a block diagram of ACMC operation for a buckconverter.

Related Documentation
1. Precision Brightness and Color Mixing in LED
Lighting Using Discrete Current Sense Amplifiers
2. Current Sensing in an H-Bridge
3. Switching Power Supply Current Measurements

The noise sensitivity of PCMC methodology isimproved using ACMC to acceptable performancelevels with the INA240 high CMRR helping to provide
additional transient reduction. The INA240 highcommon–mode range is required to make the inductor
current measurement and allows usage of the current
amplifier in a wide–range of output voltages. The
41

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Current Mode Control in Switching Power Supplies

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Application Brief

Switching Power Supply Current Measurements

There are many different switching power supply
topologies available to meet system power
requirements. DC–DC switching converters reduce ahigher voltage DC rail to a lower voltage DC rail.
These converter architectures include buck, boost,buck-boost, and flyback topologies. DC–AC switching
converters convert a DC input voltage to an AC output
voltage.
As implied by their name, switching converters
employ various switches, transistors/FETs and/or
diodes, to translate the input voltage to the desired
output voltage at high system efficiency levels.
The switching nature of these converters present
challenges in trying to accurately measure the current
waveforms. Voltage node requirements, system
control requirements, and measurement drift areareas to consider when selecting current sense
amplifiers.
Voltage Node Requirements
Each node in the circuit architecture has a different
common-mode voltage and behavior. Measuring
currents at each of these locations has different
characteristics that the measurement circuit must take
into consideration. Figure 1 illustrates the different
nodes of a buck/step-down converter. The circuit
shows a basic circuit consisting of a half H–bridge
output stage with a low-pass filter constructed froman inductor and capacitor. The control circuitry, output
stage drivers, and load are not shown.
1

3

L

2

C

LOAD

4

Figure 1. DC–DC Switching Power Supply – Buck
Architecture
Node 1 voltage is tied to the input supply of theconverter. This is the high voltage the converter
is “stepping-down” to the lower output voltage.
Current measurements at this node are measuring

the current flowing through the high-side devicesof the half H–bridge and are used primarily forovercurrent/short–circuit detection with a comparator.
Any measurements being made at this node require
high common-mode circuits with the performance tomeasure a small differential voltage.
Node 2 is the mid-point of the half H–bridge anddisplays the pulse-width modulation (PWM) signal thatswitching power supplies are based around. Current
measurements at this location provide the inductor
current for system control and overcurrent/short–circuit detection. The voltage transitions between
the upper voltage and ground (or negative supply)in the PWM ratio that is averaged to produce thecorrect output voltage. Node 2 voltage will have sharpcommon-mode transitions, so measurements here
need to be able to handle the transition voltage inmagnitude as well as suppressing the transient in the
output waveform.
Node 3 voltage is the converter output voltage, which
is a DC voltage level with a small voltage ripple
when observed on oscilloscope. Measurements at thislocation will have similar requirements to Node 1 andprovide the inductor current for use in system control
and overcurrent/short–circuit detection. Even though
Node 3 voltage is less than Node 1, the desired
output voltage level may still require measurement
circuitry to handle a high common-mode voltage.
Node 4 voltage is tied to ground of the circuit.
This node will see low, close to ground, commonmode levels so measurements at this location havea reduced set of requirements compared with thepreviously mentioned locations.
Other DC–DC switching architectures have similar
behavior as the nodes described above, although they
may be at different locations in the converter circuitry.
Measurement Drift Requirements
Switching power supplies are highly efficient circuits
for voltage level translation, but there are still power
losses in the conversion. These power losses are
system efficiency losses that manifest as thermal
generation or heat. Depending on the power levels of
the converter, this can be a significant thermal source.

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The current typically used is the inductor current in
the converter (see Figure 2). This provides a much
faster internal loop to run in parallel with the voltage
feedback loop. In general, one of the down sides ofcurrent mode feedback is the susceptibility to noise/transients on the signal.

RSENSELC
LOAD

INA240

Table 1. Power Dissipation Summary(1)Parameter

Gain
20V/V

100V/V

Input Voltage (mV)

150

30

15

15

3

1.5

Power dissipated (W)

1.5

0.30

0.15

Full-scale output voltage = 3 V and current measurement =10A

System Control and Monitoring Requirements
Most switching power supplies employ closedfeedback systems to provide stable, well regulated
power. In order to provide optimized feedback control,
precision measurements are desired. Amplifier
specifications, like offset and gain errors, cansignificantly influence the regulation ability of thecontrol system. Different feedback methods are used
depending on the system requirements and desiredcomplexity of the circuitry. Additionally, system powermonitoring is a growing need as designs optimize
and report the power consumption during different
operating modes of the end equipment.
Voltage mode feedback compares a scaled versionof the output voltage to a reference voltage to obtain
the error voltage. This feedback method is relatively
simple, but provides slow feedback as the system
must allow the output voltage to change before
adjustments can be made. Current measurementsfor voltage mode feedback generally monitor theload currents and determine if any short–circuits arepresent. The most important current amplifier criteria
for voltage mode feedback converters is the commonmode output voltage of the converter. The output
voltage on these converters ranges from low voltages
used for microprocessors and low voltage digital
circuitry (1.8 V to 5 V) to high voltages used for 48
V or higher systems. The output waveform, while after
the filter, may still contain noise/transients that candisturb or cause errors in the measurement.
Current mode feedback adds a feedback loop to
the control system that utilizes the system current.

43

Switching Power Supply Current Measurements

To Feedback/Control Circuit

200V/VRSENSE (mΩ)

(1)



+

The INA240 has a-low thermal drift spec, whichmeans that the current measurement does notchange significantly due to heat generation. To
further reduce the heat generated, the INA240
comes in different gain versions, which allow
for the decrease in value of the current sense
resistor. Traditional amplifiers can have significant
decreases in performance as amplifier gain increases.
By contrast, all gains versions of the INA240
have excellent electrical specifications allowing theachievement of high performance levels acrossdifferent gain variants. Table 1 provides a comparisonof the power dissipation difference between gains.

Figure 2. Current Sensing for Power Supply
Control Feedback
Current mode feedback is generally split into peakcurrent mode control and average current mode
control. Peak current mode control utilizes theinductor current directly and therefore any noiseor transients on the signal cause disturbances in
the feedback loop. The INA240 is designed withhigh CMRR, which helps to attenuate any potential
disturbances or noise due to the input signal.
Alternative Device Recommendations
Based on the system requirements, additional
devices are available that may provide the needed
performance and functionality. For applications
requiring the lower performance levels than the
INA240, use the INA290. The LMP8481 is a bidirectional current sense amplifier used for highcommon-mode voltages that do not require theamplifier to include ground in the input voltage range.
Table 2. Alternative Device Recommendations
DeviceOptimized Parameters

Performance Trade-Off

INA253Integrated Low Inductive+/-15A at TA= 85°C
Shunt: 2mΩ, PWM rejection

INA290Wider Common-Mode Input
Range, Small Package
No Enhanced PWM Rejection(SC-70)

LMP8481

Wide Common-Mode Input
Range, Low power

No Enhanced PWM Rejection,
Common-mode range does notinclude ground

Related Documentation
1. Precision Brightness and Color Mixing in LED
Lighting Using Discrete Current Sense Amplifiers
2. Current Sensing in an H-Bridge
3. Benefits of a Low Inductive Shunt for Current
Sensing in PWM Applications

SBOA176C – DECEMBER 2020 – REVISED MARCH 2022
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Copyright © 2022 Texas Instruments Incorporated

____________________________________________________

Increase Measurement Accuracy Using High-Speed
Amplifiers for Low-Side Shunt Current Monitoring
Author: Leaphar Castro

The need to accurately and quickly detect the load
current through a low-side shunt resistor is a criticalapplication in systems requiring overcurrent, feedback
control loops, battery monitoring, and power-supply
monitoring. Load current is often measured using lowside current sensing, which is when the voltage ismeasured across a shunt-resistor that is placed
between the load and ground. One common way todiscretely implement low-side current monitoring is touse a current-sense amplifier in a difference
configuration, as shown in Figure 1.
VCC
+

VEE
+

5V
GND

VCC

0V
GND

5 k

VCC

I_IN

GND

100 

R_Sense

15 m

GND

100 

OPA354

Out

VEE
5 k

Figure 1. Low-Side Current Sensing Test Circuit
Using the OPA354
Traditionally, this low-side current measurement isdone with a dedicated current sense amplifier or alower-speed amplifier connected to an external shuntresistor. However, in applications that are required todetect a small, high-speed transient pulse, theseamplifiers tend to lack the adequate bandwidth needed

SBOA298A – May 2018 – Revised August 2019
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to replicate the pulse accurately in a single gain stage.
A possible solution is to use multiple gain stages witha lower bandwidth device, thus increasing the amountof components and potentially increasing the shunt
resistance in order to use a smaller gain. By having alarge shunt-resistor, you introduce noise to your signal,
increase the power dissipation, and cause ground
disturbances. Instead, an alternative solution is to use
a single high-speed amplifier. By using the high-speed
amplifier. you have more gain-bandwidth, which allows
you to use a single high-gain stage with a small shuntresistor. For current sensing applications, you want tochoose an amplifier with low offset and noise so that it
does not degrade the accuracy of low-voltage
measurements. Consider a widely used op-amp suchas the OPA365. This device has a maximum input
offset voltage as of 200 µV and an input voltage noiseof 4.5 nV/√Hz at 100 kHz. Using an amplifier such as
OPA365 allows you to implement the circuit in a single
high-gain stage, save board space, keep the shuntresistor low, and enable driving an analog-to-digitalconverter (ADC) with a single device. The OPA365 isavailable in an AEC-Q100 version (OPA365-Q1) that
supports automotive applications.
Choosing the correct amplifier simplifies detection ofhigh-current spikes that may cause damage to thesystem or reduce motor and servo efficiency, all while
maximizing system efficiency. There are several
benefits to using a high-speed amplifier in currentsensing circuit. For example, in applications such as
power-supply monitoring, the duration of the pulse
may be as low as 1 µs. Without being able to detect
these transients, short-duration pulses may gounnoticed, and thus cause glitches or potential
damage to the rest of the system. As shown in Figure
2, with a short-duration 1-µs pulse input in a gain of
50, the OPA354 is able to reach 3-V output and is able
to replicate the original input signal much closer than a
400-kHz or a 20-MHz bandwidth op amp. As Figure 3
shows, 100-nA input pulse in a gain of 50 isintroduced, and again the output response of the
OPA354 is much closer than the other two devices.

Increase Measurement Accuracy Using High-Speed Amplifiers for Low-Side
Shunt Current Monitoring Author: Leaphar Castro

Copyright © 2018–2019, Texas Instruments Incorporated

44

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microseconds. Use a high-speed amplifier for motorcontrol applications to provide a fast and precise
current measurement for the best dynamic motor
control, minimum torque ripple, and minimal audible
noise.

Figure 2. Output Response With a 3-A, 1-µs Input
Into 15 mΩ With a Gain of 50 vs an Integrated andLower-Bandwidth Device

For maximum system efficiency when using an op
amp to measure a small differential voltage signal fromthe shunt-resistor, make sure the op amp has enoughbandwidth to make a precise and accurate
measurement without introducing error to the signal.
Measuring short duration pulses are a challenge, but
by using a high-speed amplifier, high slew rates andplenty of bandwidth are available to track the input
signal. This article used the OPA354 as an example,
but there are many other available amplifiers offeredby Texas Instruments. For automotive applications that
require AEC-Q100 devices, and applications that
require higher supply ranges or higher bandwidth, see
Table 1. The amplifiers listed inTable 1 give alternative
recommendations with optimized parameter benefits,
and what the performance trade-offs are of using eachof the devices.
Table 1. Alternative Device Recommendations

Figure 3. 100-nA Pulse Input Into 15 mΩ With aGain of 50 vs an Integrated and Lower-Bandwidth
DeviceIn another example, a three-phase inverter shuntresistor is sensing large negative phase voltages.
These PWM duty cycles tend to be very small (around2 µs). The current sense amplifier must be able tosettle to < 1% in this time frame, and in many cases
drive an ADC. In applications such as three-phase
inverters, maintain low distortion at the maximum rate
at which the output changes with respect to time. In
general, high-speed amplifiers offer slew rates > 25
V/µs and fast settling times of < 0.5 µs. These features
make high-speed amplifiers a great choice when ahigh rate of change exists in the output voltage that iscaused by a step change on the input in the form ofshort current pulses. High slew rate, larger bandwidth,and fast settling high-speed amplifiers contribute tokeeping the detection time down to a few

45

DeviceOptimized Parameters

Performance
Trade-Offs

OPA836Higher bandwidth,
lower power consumption

IN to –V rail,slightly less output
current

OPA2836-Q1

Dual channel,
higher bandwidth,
lower power consumption,
automotive qualification

IN to –V rail,slightly less output
current

OPA354
OPA354-Q1

Higher bandwidth,
higher slew rate,
higher output current,
automotive qualification(Q1)

Slightly higher
offset and power
consumption

LMH6618

Higher supply (maximum),higher bandwidth,
lower IQ

Slightly higher
noise and less
output current

LMH6611Higher supply (maximum),higher bandwidth,
higher slew rate

IN to –V rail,slightly higher
power consumption

Single, dual, quad channels,
higher supply (maximum),IN to –V rail,
LMH6642lower IQ ,slightly higher
LMH6642Q-Q1
automotive qualification
noise
(Q1)

Increase Measurement Accuracy Using High-Speed Amplifiers for Low-Side
Shunt Current Monitoring Author: Leaphar Castro

SBOA298A – May 2018 – Revised August 2019
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Application Brief

Extending Beyond the Max Common-Mode Range ofDiscrete Current-Sense Amplifiers

Arjun Prakash, Current Sensing Products

The system cost solution of high voltage, high-sidecurrent sensing can be expensive considering a goalof <1% accuracy needs to be achieved. For common
mode voltages higher than 90 V often the selectionof current sense amplifiers are limited to isolation
technology which can be expensive and BOM
extensive. Below are some of the techniques that
illustrates the extension of low voltage common modecurrent sense amplifiers beyond its maximum rating
by adding a few inexpensive external components like
resistors, diodes and PMOS FETs.

is to use precision 0.1% matched low temperaturedrift external resistor dividers.
Power Supply

Rshun
t

R1

R2

IN+

IN-

Vout = G x (V(IN+)  V(IN-))
G = R2/R1

R3

R4

Load

Power Supply

V+
Rshun
t

For high-side power supply current sensing needs, itis critical to understand the maximum voltage ratingof the power supply. The maximum power supply
voltage will drive the selection of a current sense
amplifier. The common mode voltage of the current
sense amplifier should exceed the maximum voltage
on the power supply. For example, if a current ismeasured on the 48 V power supply with a transient
voltage not exceeding 96 V a current sense amplifier
with a maximum common mode voltage supporting 96
V needs to be designed. Likewise for a 400 V supply
a common mode voltage of current sense amplifier
supporting 400 V needs to be chosen.

V-

R1

RD1
RD2
RD3

R2

IN+

IN-

R3

Vout = G x (VCMP - VCMN)
G = (R2/R1)
VCMP = V(+) x (RD2/(RD2 +RD1))
VCMN = V(-) x (RD4/(RD4 +RD3))

RD4
Load

R4

Figure 1. Extending Common Mode Range using
Resistor Dividers

Common Mode Voltage Divider Using Resistors.

Extending Common Mode Range for Current
Output Amplifiers

The simplest approach to monitor high voltage highside current sensing is a design with a low voltage
current sensing amplifier with external input voltage
dividers, for example, if a 40 V common mode voltage
amplifier is selected for a 80 V application, the 80
V input common mode needs to be divided down to
40 V common mode voltage. This voltage division
can be accomplished using external resistor dividers
as shown in the Figure 1. This is a simple design
approach and the tradeoffs are significant. The gain
error and CMRR of the amplifier are dependent
on the accuracy and the matching of the external
input divider resistors. Apart from gain error and
CMRR errors, the tolerance of the external resistors
will contribute to imbalance in input voltage causing
additional output error. This error does increase overtemperature depending on the drift specifications of
the resistors. One technique to minimize output error

In Figure 2 Zener diode DZ1 regulates the supply
voltage that the current shunt monitor operates within,and this voltage floats relative to the supply voltage.
DZ1 is chosen to provide sufficient operating voltage
for the combination of IC1 and Q1 over the expected
power-supply range (typically from 5.1 V to 56 V).
Select R1 to set the bias current for DZ1 at somevalue greater than the maximum quiescent current of

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As voltage dividers has serious consequences with
output error and degradation in performance, anotheralternative approach is to shift the ground referenceof the current output amplifier to the high voltage
common mode node as shown in Figure 2.
Figure 2 enables current sensing at higher voltages
beyond rated common mode voltage of INA168 is
60V. This technique can be extended to any voltage
beyond 60V by designing an appropriate PMOS FET(Q1).

Extending Beyond the Max Common-Mode Range of Discrete Current-Sense
Amplifiers
Copyright © 2022 Texas Instruments Incorporated

46

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IC1. The INA168 shown in Figure 2 is specified at
90 µA maximum at 400 V. The bias current in DZ1
is approximately 1 mA at 400 V, well in excess of
IC1’s maximum current (the bias current value wasselected to limit dissipation in R1 to less than 0.1
W). Connect a P-channel MOSFET, Q1, as shown tocascode the output current of IC1 down to or below
ground level. Transistor Q1’s voltage rating should
exceed the difference between the total supply and
DZ1 by several volts because of the upward voltage
swing on Q1’s source. Select RL, IC1’s load resistor,
as if IC1 were used alone. The cascode connectionof Q1 enables using IC1 well in excess of its normal
60-V rating. The example circuit shown in Figure 2
was specifically designed to operate at 400 V.
400V

5k

IN+

INA168200uA/V

DZ1
5k
IN-

Q1

400V

VOUT

Load

VsenseFigure 2. High-Side DC Current Measurements for
400-V Systems
Extending Common Mode Voltage Range forPower Monitors
System optimization and power monitoring for highvoltage systems (40 V to 400 V), if implemented
accurately can result in improvement of overallsystem power management and efficiency. Current,
voltage and system power information can bebeneficial in taking preventive steps to diagnose
faults or calculate total power consumption of thesystem. Monitoring faults and power optimization
will assist high voltage system in premature failuresand significantly lower power savings by optimizing
system shut down and wake up.
Figure 3 illustrates a methodology by using INA226 a
36 V common mode voltage power monitoring device
to be used in applications supporting 40 V to 400 V
systems. Shown in Figure 2 is the precision, rail-to-rail
op amp OPA333 used to mirror the sense voltage
across the shunt resistor on to a precision resistor
R1. OPA333 is floated up to 400 V using a 5.1 V
zener diode between its supply pins. The op amp
drives the gate of the 600 V P-FET in a current
follower configuration. A low leakage P-FET is chosen
47

+

10
-

+

RshuntVsense

RL
50K

-

10 K

5.1V
Zener
OPA333
+
RZ

210 R

R1

VsenseRshunt+to obtain accurate readings even at the low end of themeasurement. The voltage across R1 sets the draincurrent of the FET and by matching the resistor R2
in the drain of the FET to be equal to R1, VSENSE
voltage is developed across R2 (VR2). Inputs of thecurrent monitor INA226 are connected across R2 forcurrent sensing. Hence the current monitor does notneed the high common mode capability as it will only
see common mode voltages around VSENSE which
is usually less than 100mV. INA226 was chosen for
current, voltage and power monitoring as it is a highaccuracy current/voltage/power monitor with an I2C
interface. The INA226 can also sense bus voltages
less than 36 V. Since the bus voltage employed hereis 400 V, a divider is employed to scale down thehigh voltage bus to a voltage within the common
mode range of INA226. In this case a ratio of 64 ischosen and hence the bus voltage LSB can be scaled
accordingly to obtain the actual bus voltage reading.
In this case the a modified LSB of 80 mV could be
used. Precision resistors are chosen for the divider tomaintain accuracy of the bus measurement.

IN+ VBUS
IN- GND

SCL
SDA

Load

Figure 3. High Voltage Power Monitoring
Table 1. Alternate Device Recommendations
DeviceOptimized Parameter

Performance TradeOff

LMP8645HV

Bandwidth : 900kHz,
Package: SOT-23-6

Slew rate: 0.5V/uS

INA220MSOP-8 Package, I2C
Gain Error (1%), Shuntinterface, Selectable
Offset Voltage: 100uVI2C address

INA139Package: SOT-23,
Bandwidth: 4400 kHz,
cost

Offset voltage: 1mV

Related Documentation
1. Current Sensing in an H-Bridge
2. Switching Power Supply Current Measurements
3. High-Side Drive, High-Side Solenoid Monitor WithPWM Rejection

Extending Beyond the Max Common-Mode Range of Discrete Current-Sense
Amplifiers
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Application Brief

Interfacing a Differential-Output (Isolated) Amp to aSingle-Ended Input ADC

Introduction

Embedded ADCs

Whether you are sensing current in an industrial 3phase servo motor system, a battery management
system for an electric vehicle, or a photo voltaic
inverter, it is often necessary to include some sortof safety isolation scheme. Safety-related standards
define the specific isolation requirements for theend equipment associated with the particular design.
Various factors come into play when determining
what level of safety insulation (basic, supplemental,
or reinforced) is required depending on the typeof equipment, the voltage levels involved, and theenvironment that the equipment is to be installed.

Both the MSP430 and C2000 family of processors
have embedded single-ended input ADCs so thequestion becomes, How do I get this differential signal
into my single-ended data converter?

Texas Instruments offers a variety of isolated current
shunt amplifiers that are used in the previouslymentioned applications for voltage and current shuntsensing that meet either basic or reinforced insulation
requirements. For applications requiring reinforced
insulation, one such device is the AMC1301. The
output of the AMC1301 is a fully differential signal
centered around a common-mode voltage of 1.44 V
that can be fed directly to a stand-alone analog-todigital converter (ADC) as shown in Figure 1, or tothe on-board ADC found in the MSP430 and C2000
family of micro-controller devices.
Floating
Power Supply

Gate
Driver

3.3 V or
5.0 V

AMC1301GND1
RSHUNT

VDD2

VDD1

VINN

To Load

VINP

Reinforced Isolation

HV+

The simplest way to achieve this is to use only
one output of the AMC1301 leaving the second
output floating. The down side to this solution isthat only half the output voltage swing is available
to the data converter, reducing the dynamic rangeof the measurement. The analog input range to the
AMC1301 is ±250 mV. With a fixed gain of 8.2, the
VOUTN and VOUTP voltages are ±1.025 V centeredaround the 1.44-V common-mode output as shown in
Figure 2. Differentially, the output voltage is ±2.05 V.

3.3 V or 5.0 V

GND2
VOUTP
ADS7263
14-Bit ADC
VOUTN

Gate
DriverFigure 2. Differential Output Voltage
The addition of a differential to single-ended amplifier
output stage, illustrated in Figure 3, allows the full
output range of the AMC1301 to be provided to the
ADC.

HV-

Figure 1. AMC1301 Functional Block Diagram

Figure 3. Differential to Single-Ended Output

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Assuming a full scale sine wave of ±250 mV is applied
at VIN; the internal gain of the AMC1301 will provide
2.05 Vpk-pk outputs at points VOUTP and VOUTN
which are 180° out of phase. The difference between
these signals, VODIF, is 4.1 Vpk-pk. When R1 = R4
and R2 = R3 the transfer function of the output stage
is shown in Equation 1.
 R4 
 R1 
VOUT  VOUTP    VOUTN   R2   VCM
 R3 
(1)With equal value resistors for R1 through R4 in
Equation 1 and VCM set to 2.5 V, Equation 2 reduces
to:
VOUT  VOUTP  VOUTN  VCM

Design Example
The ADC12 found on the MSP430 devices havean input voltage range of 0–2.5 V when using theinternal voltage reference. Using the VOUTP from theAMC1301 would provide the ADC12 with an input
signal ranging from 0.415 V to 2.465 V, well within
the input range of the converter while only utilizing
half the input range of the AMC1301. As shownin Figure 5, utilizing a differential to single-ended
amplifier configuration with a gain of 0.5 and common
mode voltage of 1.25 V, the entire voltage range of
the AMC1301 can be applied to the ADC12.

(2)

The plots of Figure 4 show the input voltage andoutput voltages of the AMC1301 along with the output
voltage of the final differential to single-ended output
stage. Note that the differential voltage of ±2.05 V istransposed to a single-ended signal from 0.5 to 4.5 V.
Figure 5. Scaled Differential to Single-Ended
OutputAlternative Device Recommendations
The AMC1100 or AMC1200 provide basic isolation
with similar performance to the AMC1301 at a lower
price point. For applications requiring a bipolar output
option, the TLV170 is an excellent choice.
Table 1. Alternative Device Recommendations

Figure 4. Single-Ended Output Voltage
Depending on the input voltage range of the ADC,
gain or attenuation can be incorporated into thedifferential to single-ended stage to adjust the output
swing. The output common mode voltage can be
adjusted to fit the input needs of the ADC as well.

DeviceOptimized Parameter

Performance Trade-Off

AMC1100

Galvanic Isolation up to 4250
VPEAK

Lower Transient Immunity

AMC1200

Galvanic Isolation up to 4250
VPEAK

Basic Isolation versus
Reinforced

TLV170Bi-polar operation to ±18 V

Higher input bias current

Conclusion
While it is possible to use a single output of the
AMC1301 to drive a single-ended ADC, adding a
differential to single-ended op-amp stage at the output
ensures the target application will have the largest
possible dynamic range.
Related Documentation
1. Low-Drift, Low-Side Current Measurements for
Three-Phase Systems
2. Precision Current Measurements on High Voltage
Power Supply Rails

49

Interfacing a Differential-Output (Isolated) Amp to a Single-Ended Input ADC
Copyright © 2022 Texas Instruments Incorporated

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Submit Document FeedbackLow-Drift, Precision, In-Line Isolated Magnetic Motor
Current Measurements
Steven Loveless - Current Sensing Products

The demand for higher efficiency systems continues toincrease, leading to direct pressure for improvement inmotor operating efficiency and control. This focus
applies to nearly all classes of electric motors,
including those used in:• White goods• Industrial drives• Automation• Automotive applications
This is especially true in higher-power systems withelevated operating voltages. Operational
characteristics of the motor fed back into the control
algorithm are critical to ensure the motor is operating
at peak efficiency and performance. Phase current is
one of these critical diagnostic feedback elements
used by the system controller to enable optimal motor
performance.

leadframe, which creates an internal magnetic field. A
galvanically isolated sensor then measures themagnetic field, providing a measurement of the current
without any direct electrical connection between thesensor IC and the isolated phase current. Bymeasuring only the magnetic field, the sensor provides
isolation to high common-mode voltages, as well as
excellent immunity to PWM switching transients. This
results in excellent motor phase current measurements
without unwanted disturbances at the sensor output
due to large, PWM-driven input voltage steps. Figure 2
illustrates an RC-filtered TMCS1100 output waveform,
along with the motor phase voltage and current
waveforms. Only minor PWM-coupling due tomeasurement parasitics are observable, and the
TMCS1100 output tracks the motor phase current withno significant output transients due to the 300-V
switching events.

Due to the continuity of the measurement signal anddirect correlation to the phase currents, an ideal
location to measure the motor current is directly in-linewith each phase, as shown in Figure 1. Measuring
current in other locations, such as the low-side of eachphase, requires recombination and processing before
meaningful data can be used by the control algorithm.

Figure 2. Motor Phase Current Measurement withHigh Transient Immunity
To Controller

Figure 1. In-Line Current Sensing
The drive circuitry for the motor generates pulse widthmodulated (PWM) signals to control the operation of
the motor. These modulated signals subject themeasurement circuitry placed in-line with each motor
phase to large voltage transients that switch between
the positive and negative power rails every cycle. An
ideal current sensor has the ability to completely reject
the common-mode voltage component of themeasurement, and only measure the current ofinterest. In-package magnetic current sensors like the
TMCS1100 pass the phase current through a package
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The unique characteristics of an in-package magnetic
current sensor eliminate many of the challenges facedby alternative solutions to measuring motor phasecurrents. The inherent galvanic isolation provides
capability to withstand high voltage, and the hightransient immunity of the output reduces output noisedue to switching events. Current sensing
implementations without this immunity require higher
bandwidth in order to improve output glitch settling
time; a magnetic sensor can use a lower-bandwidth
signal chain without sacrificing transient immunity

Low-Drift, Precision, In-Line Isolated Magnetic Motor Current Measurements
Copyright © 2019, Texas Instruments Incorporated

Steven Loveless - Current Sensing Products50

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For applications where phase current measurements
provide over-current protection or diagnostics, the hightransient rejection of a magnetic current sensor
prevents false overcurrent indications due to output
glitches. In motor systems where closed loop motor
control algorithms are used, precise phase current
measurements are needed in order to optimize motor
performance. Historically, Hall-based current sensors
have suffered from large temperature, lifetime, andhysteresis errors that degrade motor efficiency,
dynamic response, and cause non-ideal errors such as
torque ripple. Common system-level calibration
techniques can improve accuracy at room
temperature, but accounting for temperature drift inparameters, such as sensitivity and offset, ischallenging.
Magnetic current sensing products from Texas
Instruments improve system-level performance byincorporating patented linearization techniques andzero-drift architectures that provide stable, precise
current measurements across temperature. A highprecision sensor tightly controls phase-to-phasecurrent measurement errors, maintaining accurate
feedback control and delivering a seamless user
experience.
1

Sensitivity Error (%)

0.5

5
TMCS1100A1
TMCS1100A2
TMCS1100A3
TMCS1100A4

4.5
4
3.5
3
2.5
2
1.5
1
0.5
0
-40

-20

0

20
40
60
Temperature (C)

80

100

120
D009

Figure 4. TMCS1100 Typical Output Offset AcrossTemperature
Combining high-sensitivity stability and a low offset
results in an industry-leading isolated current sensing
solution with <1% total error across the fulltemperature range of the device. A 600-V working
voltage and 3 kV isolation barrier allows the device to
fit into a wide array of high voltage systems.
Combining measurement temperature stability,
galvanic isolation, and transient PWM input rejection,
the TMCS1100 is an ideal choice for PWM-driven
applications, such as motor phase current
measurements, where accurate and reliablemeasurements are required for precisely controlled
performance.

0

Table 1. Alternate Device Recommendations
-0.5

-1
-40

-20

0

20
40
60
Temperature (C)

80

100

120

DeviceOptimized Parameter

Performance Trade-Off

TMCS1101

Magnetic Current Sensor with
Internal Reference

Lower precision, PSRR

AMC1300

Reinforced Isolation Shunt
Amplifier

Solution size, complexity

INA240Precision Shunt Amplifier withPWM Rejection

80V functional isolation

INA253

Precision Integrated-Shunt
Amplifier with PWM Rejection

80V Functional isolation, size

D006

Figure 3. TMCS1100 Typical Sensitivity Error
Across Temperature
The TMCS1100 features less than 0.3% typicalsensitivity error at room temperature, and less than
0.85% maximum sensitivity error across the entire
temperature range from –40°C to 125°C. This stability
across temperature, shown in Figure 3, provides
excellent phase-to-phase matching by minimizing the51

temperature drift of the sensor. In addition to highsensitivity accuracy, the device has less than 2 mV ofoutput offset drift, shown in Figure 4, which greatly
improves measurement dynamic range, and allows for
precise feedback control even at light loads.

Typical Offset (mV)performance. In-package magnetic current sensors
also provide a reduction in total solution cost anddesign complexity due to no requirement for external
resistive shunts, passive filtering, or isolated power
supplies relative to the high voltage input.

Table 2. Related TI TechNotes
Lit #

Title

SBOA340

Ratiometric Versus Non-Ratiometric Magnetic Signal
ChainsSBOA160

Low-Drift, Precision, In-Line Motor Current Measurements
With PWM Rejection

SBOA161

Low-Drift, Low-Side Current Measurements for ThreePhase Systems

SBOA163

High-Side Motor Current Monitoring for Over-Current
Protection

Low-Drift, Precision, In-Line Isolated Magnetic Motor Current Measurements
Steven Loveless - Current Sensing Products

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Application Brief

Application Brief

Current Sensing in Mobile Robots

Kyle Stone

Current Sensing

Introduction
Mobile robots are widely used in warehouse settings. These mobile robots help to increase efficiency within
warehouses by moving quickly around a facility and collecting items that are needed to fulfill orders in a timely
manner. By using these mobile robots, warehouse operators can have reduced overhead cost, a continuous
faster output, and warehouses can potentially be organized in more efficient configurations, as these mobile
robots can reach places humans cannot easily access.
Mobile robots start at their home base where robots are charged and are stored. When the robot is called upon,
the robot can move around the warehouse to pick up the requested items, and bring those items to a desired
location, where either a human or another robot such as industrial robot can take the items to an assemblyline or shipping line. The mobile robot typically uses brushless DC motors to move. An accurate phase current
sensing is critical in motor control. A poor current sensing can lead to large torque ripple, audible noise, andinefficiency. Figure 1 illustrates where current sensing plays a role in motor-drive applications.
Vbus

High-side DC link

+

–

+

+

+

–

–

–

D1
Q1

D3
Q3

High-side

D5
Q5
I_U

I_W

+

V

–

+

–

D4
Q4

+

–

D2
Q2

I_V

U

W

D6
Q6
InlineLow-side DC link

+

+

+

–

–

–

Low-side+–Figure 1. Methods of Motor Current Sensing in Mobile Robots
There are three methods of motor current sensing with their own positives and negatives as shown in Table
1. The best location to measure the motor current is directly inline with each phase due to continuity of signal
measurement and direct correlation to the phase currents. In-line current sensing comes with the challenge
where each motor phase is subjected to common-mode voltage transitions that can switch between large
voltage levels over very short time periods. Current measurement in other locations, such as the low-sideof each phase, requires recombination and processing before meaningful data can be utilized by the control

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Application Brief

algorithm. INA241A is designed for in-line motor current sensing. INA241A offers high CMRR of 166 dB andenhanced PWM rejection allowing for minimal error at the output in switching systems.
Table 1. Current Sensing in an H-Bridge
Current Measurement

Positives

Negatives

High-side

Detect shorted load from battery for diagnostics

High voltage common-mode amplifier

InlineDirect motor current measurement, low bandwidth
amplifierHigh dv/dt signals. PWM settling time.

Low-sideLow cost, low common-mode voltage

Unable to detect shorted load.

The mobile robots typically have onboard 48-V lithium-ion batteries, and can be charged wirelessly or wired.
Charging currents and discharging currents can be monitored through Texas Instruments’ line of digital powermonitors such as the INA228 and INA238. The INA228 can monitor current, voltage, power, energy, or charge
up to 85-V common-mode input range with 20-bit resolution through an I2C output. This allows for the robot tomonitor the battery levels to the onboard computer. INA228 can monitor battery level and when the battery levelruns low, the mobile robot can report back to the home base to be re-charged.
There are several other subsystems within the mobile robot, such as DC/DC converters, onboard computers,
lighting systems, radars, and so forth, that can use current sensing. DC/DC converters can use current monitors
in the system such as the INA296A to monitor the safe level of current and to make the system more efficient.
The onboard computer is the brain of the mobile robot, and typically operates on a 5-V rail. The onboard
computer can leverage current sensing with a digital power monitor such as the INA219, to monitor current andvoltage into the system to report back health or power usage in the system. Current monitors can also be used
to monitor various peripherals on the robot such as the lighting and radar systems.
Using current monitors can verify these subsystems are operating correctly for safely preventing an incident
with a human or physical structure. Monitoring current through the peripheral systems can enable the system
to detect a malfunction and can have the robot return to home base for maintenance. The INA281 or INA296A
can be used to monitor the current flow in these peripherals. Figure 2 shows one possible way current sensing
can be used in point-of-load (POL) applications where understanding the current going to a specific load in thesystem is important. This can be used for diagnostics, safety, and protection.

2

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Application Brief
Shunt resistor
Load
3.3V DC/DC
Load switch

Digital power monitor

Shunt resistor
Load
5V DC/DCEMI filter
Battery

Load switch

Main switch

Digital power monitor

Shunt resistor
Load
12V DC/DC
Load switch

Digital power monitor

Figure 2. Power Monitoring at POL for Power System in Robotics
Conclusion
In conclusion, mobile robots are generally used in warehousing settings to reduce human involvement andspeed up the movement of goods within the facility. Safety and efficiency are critical components of mobile
robots. Leveraging various current-sensing techniques within the subsystems in motors, batteries, onboard
computers, and peripheral systems can help these robots to operate safely and efficiently.
Alternate Device Recommendations
The INA241B is a high-precision, accurate analog current-sense amplifier. INA241B can be used in high-voltage
bidirectional applications paired with 1.1-MHz bandwidth to offer fast response time with precise control for
in-line control within H-bridge applications. The INA241B can measure currents at common-mode voltages of –5
V to 110 V and survive voltages between –20 V to 120 V, making the INA241B device an excellent choice formany systems.
The INA253 is an ultra-precise current-sense amplifier with an integrated low-inductive, precision 2-mΩ shuntwith an accuracy of 0.1% and a temperature drift of < 15 ppm/°C. The INA253 is limited to applications that need
< ±15 A of continuous current at TA = 85°C. The INA253 integrated shunt is internally Kelvin-connected to the
INA240 amplifier. The INA253 provides the performance benefits of the INA240 amplifier with the inclusion of a
precision shunt providing a total uncalibrated system gain accuracy of < 0.2%.
The INA281 can be used in high-voltage applications such as high-side current sensing in a motor. The INA281
can measure currents at common-mode voltages of –4 V to 110 V and survive voltages between –20 V to 120 V,
making the device versatile for a variety of applications where voltage can swing negative.
An option for low-side sensing is the INA381 which is a cost-optimized current-sense amplifier with an integrated
comparator which serves to reduce PCB footprint size and simplifies design.
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Application Brief

Table 2. Alternate Device Recommendations
DeviceOptimized Parameter

Performance Trade-Off

INA241B

Vcm range: –5 V to 110 V Bidirectional

Slightly lower accuracy compared to INA241A

INA281

Vcm range: –4 V to 110 V

Unidirectional

INA381

Integrated Comparator

Vcm limited to 26 V

INA253Integrated shunt 2 mΩ, VCM range: –4 V to 80 V

±15-A maximum continuous current

Table 3. Related TI Application Briefs

4

Literature Number

Description

SBOA160

Low-Drift, Precision, In-Line Motor Current Measurements With PWM
Rejection

SBOA176

Switching Power Supply Current Measurements

SBOA163

High-Side Current Overcurrent Protection Monitoring

SBOA555

Current Sensing in Collaborative and Industrial Robotic Arms

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Current Sensing in Mobile Robots
Copyright © 2022 Texas Instruments Incorporated

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Application Brief

Application Brief

Current Sensing in Collaborative and Industrial
Robotic Arms

Kyle Stone, Guang Zhou, Sanjeev Manandhar

Current Sensing

Introduction
Collaborative robots and Industrial robots are the dominant robot technologies driving factories towardautomation and increasing efficiency and throughput of the factories. Factories are able to build their end
products at an ever-faster rate to meet the demand of the customers by implementing these semi- and fullfactory automation technologies.
Collaborative Robots
Collaborative robots are human-assisted robots that typically work only with human interactions. These robots
assist humans in lifting payloads in the range of 6 kg to 25 kg and greater to help reduce human fatigue,
while increasing production speed. The collaborative robot is typically operating at voltages lower than 80 V,
with most systems operating in the 48-V to 50-V range due to direct human interaction. These systems are
sometimes isolated and requirements are based on the system design. Typical current ranges for these systems
are between 10 A to 30 A depending on the circuit node. Current sensing in collaborative robots is typicallyused for motor control within the axis, where a device is monitoring the in-phase current of the electric motors asshown in Figure 1.
Vbus

High-side DC link

+

–

+

+

+

–

–

–

D1
Q1

D3
Q3

High-side

D5
Q5
I_U

I_W

+

V

–

+

–

D4
Q4

+

–

D2
Q2

I_V

U

W

D6
Q6
InlineLow-side DC link

+

+

+

–

–

–

Low-side+–Figure 1. Methods of Motor Current Sensing in Collaborative and Industrial Robots
An accurate phase current sensing is critical in motor control. Poor current sensing can lead to large torqueripple, audible noise, and inefficiency. There are three methods of motor current sensing with their own positives
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Application Briefand negatives as shown in Table 1. The best location to measure the motor current is directly inline with eachphase due to the continuity of signal measurement and direct correlation to the phase currents. In-line current
sensing comes with the challenge where each motor phase is subjected to common-mode voltage transitions
that can switch between large voltage levels over very short time periods. Current measurement in otherlocations, such as the low-side of each phase, requires recombination and processing before meaningful data
can be utilized by the control algorithm.
Table 1. Current Sensing in an H-Bridge
Current Measurement

Advantages

Disadvantages

High-side

Detect shorted load from battery for diagnostics

High-voltage common-mode amplifier

InlineDirect motor current measurement, low bandwidth amplifier

High dv/dt signals. PWM settling time.

Low-sideLow cost, low common-mode voltage

Unable to detect shorted load

Board space is highly constrained in collaborative robots, so a small-footprint device is desired. Since isolation
is typically not a requirement, a device such an the INA241A is an excellent choice for an in-line current-sensing
application because the INA241A offers high CMRR and enhanced PWM rejection allowing for minimal error inswitching systems in a collaborative robot. The INA241A is packaged in a small SOT-23 (DDF) 8-pin packagemeasuring 2.95 mm × 2.95 mm (8.70 mm2) with the leads. If the application does require isolation, then a device
such as the TMCS1108 (a Hall-effect current sensor), provides functional isolation up to 100 V.
Industrial Robots
Industrial robots are very large robots that are found in car factories and other manufacturing facilities where
heavy lifting is required to pick and place large products. Industrial robots help bring a level of safety to a
manufacturer because these robots are moving very large items without the need for human interaction, and canbe done in a very controlled manner. The industrial robots typically operate in the AC domain with voltage levels
between 400 V to 600 V, which are common AC voltage levels in large manufacturing facilities. The current
levels generally range from 35 A to 250 A dependent upon what the robot is moving around the facility. Current
sensing is typically done within a cabinet near the robot, so space is less of a concern in these systems. The
current monitoring is usually done in-phase with the motors controlling the robot. Given the high-voltage present
in industrial systems, isolation is generally required to separate the high-voltage levels that are dangerous to the
low-voltage circuit systems and to humans. Today, current sensing is typically done with isolated amplifiers suchas the AMC1306.
One other common place where current sensing is required in industrial robots is in the coil drive brake release
unit. Coil drive is used for releasing the brake friction disks once the motor moving the joints has stopped or toprovide dynamic stopping in an emergency event. The magnetic field in the coil drive keeps two spring-loaded
friction disks away from each other so that rotor can turn freely. When flow of the current stops, the two braking
friction disks are pressed against each other with the help of the loaded springs to stop the rotor. Figure 2
shows a low-side current sensing used in a coil drive in a brake release unit. Low-side current sensing gives
more choices of current-sensing devices but due to the inductive nature of the coil, inputs of the current-sense
amplifier can be subjected to negative voltage during switching. In such an event, a current-sensing device isrequired to survive the negative input voltage.

2

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Application Brief

Friction
Disks
SpringRotor and Shaft

Field coil+–
Current sense
amplifierFigure 2. Low-Side Current Sensing in Coil Drive for Brake Release Unit
Conclusion
In conclusion, both collaborative and industrial robots generally both use current sensing to monitor the in-phasecurrent of the electric motor in the various robots. The main differences are the need for isolation, the level ofpower, and the amount of weight the robot can lift, hence the difference in requirements for current-sensing
devices. Industrial robots require current sensing in the coil drive to brake and stop motor. Collaborative robots
generally do not need isolation, have power levels that do not exceed 2.0 kW, and typically lift payloads between
6 kg to 25 kg. While industrial robots generally do need isolation, their power levels that can range from as little
as 3 kW up to and beyond 125 kW, and lift from 20 kg to a few thousand kilograms.
Alternate Device Recommendations
The INA241B is a high-precision, accurate analog current-sense amplifier. The INA241B can be used in highvoltage bidirectional applications paired with 1.1-MHz bandwidth to offer fast response times with precise control
for in-line control within H-bridge applications. The INA241B can measure currents at common-mode voltages of–5 V to 110 V and survive voltages between –20 V to 120 V, making the INA241B an excellent choice for manysystems.
The INA253 is an ultra-precise, current-sense amplifier with an integrated low inductive, precision 2-mΩ shuntwith an accuracy of 0.1% and a temperature drift of < 15 ppm/°C. The INA253 is limited to applications that need
< ±15 A of continuous current at TA = 85 °C. The INA253 integrated shunt is internally Kelvin-connected to the
INA240 amplifier. The INA253 provides the performance benefits of the INA240 amplifier with the inclusion of a
precision shunt providing a total uncalibrated system gain accuracy of < 0.2%.
The INA281 can be used in high-voltage applications such as high-side current sensing in a motor. The INA281
can measure currents at common-mode voltages of –4 V to 110 V and survive voltages between –20 V to 120 V,
making the INA281 versatile for a variety of applications where voltage can swing negative.
An option for low-side sensing is the INA381. This device is a cost-optimized current-sense amplifier with an
integrated comparator which serves to reduce the PCB footprint size and simplify the design.
Table 2. Alternate Device Recommendations
DeviceOptimized Parameter

Performance Trade-Off

INA241B

Vcm range: –5-V to 110-V Bidirectional

Slightly lower accuracy compared to INA241A

INA281

Vcm range: –4 V to 110 V

Unidirectional

INA381

Integrated Comparator

Vcm limited to 26 V

INA253Integrated shunt 2 mΩ, VCM range: –4 V to 80 V

±15-A maximum continuous current

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Application Brief

Table 3. Related TI Application Briefs

4

Literature Number

Description

SBOA160

Low-Drift, Precision, In-Line Motor Current Measurements With PWM
Rejection

SBOA176

Switching Power Supply Current Measurements

SBOA163

High-Side Current Overcurrent Protection Monitoring

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Application Brief

How to optimize PoE systems using discrete current
sensing

Power over Ethernet (PoE) describes several
standards that pass power along with data on
twisted-pair Ethernet cabling. PoE allows a single
cable to provide both data connection and power
to devices such as wireless access points (WAPs),
Internet Protocol (IP) cameras, and voice-overInternet Protocol (VoIP) phones.
Power sourcing equipment (PSE) such as network
switches or video recorders are used to power
powered devices (PDs). However, many PDs havean auxiliary power connector for an optional external
power supply, which often acts as backup power.
PoE offers several classes from one to eight, allowing
input powers between 4W and 71W. Powered devices
must be designed so that they do not exceed the
PoE class specification chosen. If a powered device
exceeds its PoE class limit, the PSE turns off the PD.
There are several methods to avoid PSE shutdown.
One solution would be to characterize the load bymeasuring the maximum power consumption of every
subsystem in the PD, and designing for a PoE
class that is within that characterized peak power toguarantee that the powered device never exceeds the
PoE class limit. However, this method is not ideal
because it requires more characterization and theselection of an arbitrarily high PoE class.
Suppose designers chose not to characterize theirsystems for the highest possible power consumption
and want to dynamically control system power
consumption to stay within a lower PoE class limit,
in this case, their circuit design would require current
sensors.
Current sensors can monitor DC/DC converter current
and report to an MCU or PMIC that controls thevarious subsystems within a PD, throttling power, andcycling functionality to avoid exceeding the PoE classlimit.

CameraIR LEDs
PTZ Motor

PoE PD
Controller

DC/DC
Controller

MCU

Figure 1. Current sensor in a PoE-powered device(IP camera)
Flyback converters are a common choice for DC/DC
conversion in low-power applications like PDs dueto their low cost and BOM count. These DC/DC
converters reduce the voltage from 48 V to 12 V.
Current sensors can be placed in several locations
around the flyback transformer before the load.
Measuring current on the primary and high-voltage
side of the flyback offers the greatest accuracy as
the power seen here includes losses in the DC/DC.
However, designers must select a higher commonmode input range capable device like the INA238 toaccommodate the 44-V to 57-V rail.
Low-side current sensing on the primary side offers
diminished accuracy as this option does not include
power losses in the transformer. Still, these current
sensing devices (like the INA180) do not require highcommon-mode voltage capability. Current sensing
on the secondary side of the transformer also
allows designers to choose lower common-mode
input voltage devices, but the sensor will not include
power losses in the flyback converter. This leads
to diminished current sensing accuracy because
designers must estimate or characterize power
losses in their DC/DC converter to know the power
consumption of the entire PD.
The next selection is the technology of the current
sensor. Digital power monitors like the INA219 canmeasure bus voltage and current, multiplying these to
output a power calculation over I2C. Having power
information means designers can more accurately
and easily know how close the powered device is to
the PoE class limit.
The second option is to use an analog-output current
sense amplifier like the INA180 which will not give bus

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voltage information, so if the rail voltage fluctuates,
designers will not be able to know the total power
consumption of the PD with as great accuracy.
Ultimately, this power or current information
communicates to a microcontroller or SoC. This
microcontroller or SoC is responsible for making
decisions about turning off or throttling power andcurrent to downstream electronic subsystems whencurrent reaches too close to the class limit. So in an
IP camera, for example, the MCU or SoC could turnoff the pan-tilt-zoom (PTZ) motor, heater, or IR LEDs
when power consumption gets too close to the classlimit.
Current sensors can be used for other uses
in powered devices. Specifically for IP cameras,
subsystem current can be monitored. Often IP
cameras are used outside in cold weather conditions
and heaters must be implemented. Power is aleading indicator for temperature for resistive heating,therefore digital power monitors or current sense
amplifiers can be used to actively control heating
elements. Current sensing can also be used for safetyand diagnostics in PTZ servo/stepper motors.
Additionally, IP cameras often have auxiliary power
inputs in the form of 24 Vac and 12VDCcoaxial inputs.
Current sense amplifiers can be used with a FET ina simple e-fuse configuration on these input rails tomonitor if current exceeds a threshold, triggering the
FET and turning the device off to protect downstream
electronics.
Related Documentation:
1. Texas Instruments, Getting Started with Digital
Power Monitors application note
2. Texas Instruments, Integrating the Current
Sensing Signal Path application brief

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Additional resources
Current Sense Amplifier Overview
Explore TI’s portfolio of current-sense amplifiers.
Current Sense Amplifier Comparison and Error Calculator
Compare up to five of TI’s current-sense amplifiers and calculate the residual sum-of-squares error based on the devices
selected and user-input system level parameters.
Power Monitor Tool
Input design constraints to determine the correct digital power monitor to use.

E2E is trademark of Texas Instruments.
All other trademarks are the property of their respective owners.

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