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High-or Low-Side Measurement,
Bi-Directional CURRENT/POWER MONITOR with I2C™ Interface
Check for Samples: INA226

FEATURESDESCRIPTION

•
•
•
•

The INA226 is a current shunt and power monitor
with an I2C interface. The INA226 monitors both ashunt voltage drop and bus supply voltage.
Programmable calibration value, conversion times,
and averaging, combined with an internal multiplier,enable direct readouts of current in amperes andpower in watts.

1

23

•
•
•
•

SENSES BUS VOLTAGES FROM 0V TO +36V
HIGH- OR LOW-SIDE SENSINGREPORTS CURRENT, VOLTAGE, AND POWER
HIGH ACCURACY:– 0.1% Gain Error (Max)– 10μV Offset (Max)CONFIGURABLE AVERAGING OPTIONS
16 PROGRAMMABLE ADDRESSESOPERATES FROM 2.7 to 5.5V POWER SUPPLYMSOP-10 PACKAGEAPPLICATIONS
•
•
•
•
•
•
•

SERVERSTELECOM EQUIPMENTCOMPUTERSPOWER MANAGEMENTBATTERY CHARGERS
POWER SUPPLIESTEST EQUIPMENT

The INA226 senses current on buses that can varyfrom 0V to +36V, while the device obtains its powerfrom a single +2.7V to +5.5V supply, drawing atypical of 330μA of supply current. The INA226 is
specified over the operating temperature rangeof –40°C to +125°C. The I2C interface features 16
programmable addresses.
RELATED PRODUCTS
DESCRIPTIONDEVICE

Current/Power Monitor with Watchdog, Peak-Hold,and Fast Comparator Functions

INA209Zerø-Drift, Low-Cost, Analog Current Shunt Monitor
Series in Small Package

INA210, INA211,
INA212, INA213,
INA214Zerø-Drift, Bi-Directional Current Power Monitor with
Two-Wire Interface

INA219High or Low Side, Bi-Directional Current/Power
Monitor with Two-Wire Interface

INA220Power Supply(0V to 36V)HighSide
Shunt

CBYPASS
0.1mF
VS(Supply Voltage)

VBUS
INA226

SDA
SCL

´

Load

Power RegisterV

2

Current Register
ADC

LowSideShunt

I

Voltage Register

IC
Interface
Alert
A0

Alert Register

A1

GND

High-or Low-Side Sensing
1

Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of Texas
Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
I C is a trademark of NXP Semiconductors.
All other trademarks are the property of their respective owners.
2

2

3

PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of the Texas
Instruments standard warranty. Production processing does notnecessarily include testing of all parameters.

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This integrated circuit can be damaged by ESD. Texas Instruments recommends that all integrated circuits be handled withappropriate precautions. Failure to observe proper handling and installation procedures can cause damage.
ESD damage can range from subtle performance degradation to complete device failure. Precision integrated circuits may be more
susceptible to damage because very small parametric changes could cause the device not to meet its published specifications.

PACKAGING INFORMATION (1)(1)

PRODUCT

PACKAGE-LEAD

PACKAGE DESIGNATOR

PACKAGE MARKING

INA226AIDGSMSOP-10

DGS

226

For the most current package and ordering information see the Package Option Addendum at the end of this document, or see the
INA226 product folder at www.ti.com.

ABSOLUTE MAXIMUM RATINGS (1)Over operating free-air temperature range (unless otherwise noted).
Supply Voltage, VS

INA226UNIT

6

V

Differential (VIN+) – (VIN–) (2)–40 to +40

V

Common-Mode–0.3 to +40

V

SDA

GND – 0.3 to +6

V

SCL

Analog Inputs,
VIN+, VIN–

GND – 0.3 to VS + 0.3

VInput Current Into Any Pin

5

mA

Open-Drain Digital Output Current

10mA

Storage Temperature–65 to +150

°C

Junction Temperature

+150

°C

Human Body Model (HBM)

2500

V

Charged-Device Model (CDM)

1000

V

Machine Model (MM)150

V

ESD Ratings

(1)
(2)

2

Stresses above these ratings may cause permanent damage. Exposure to absolute maximum conditions for extended periods may
degrade device reliability. These are stress ratings only, and functional operation of the device at these or any other conditions beyond
those specified is not implied.
VIN+ and VIN– may have a differential voltage of –40V to +40V; however, the voltage at these pins must not exceed the range –0.3V to+40V.

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ELECTRICAL CHARACTERISTICS: VS = +3.3V
Boldface limits apply over the specified temperature range, TA = –40°C to +125°C.
At TA = +25°C, VIN+ = 12V, VSENSE = (VIN+ – VIN–) = 0mV, VBUS = 12V, unless otherwise noted.
INA226
PARAMETERCONDITIONS

MIN

TYP

MAX

UNIT

INPUT
Shunt voltage input range-81.9175

81.92

Bus voltage input range (1)036Common-mode rejection

CMRR

Shunt offset voltage, RTI (2)VOS

VIN+ = 0V to +36V

126

vs Temperature
vs Power supply

PSRR

Bus offset voltage, RTI (2)VOSVS = +2.7V to +5.5V

vs Power supply

V

140

dB

±2.5

±10

μV

0.02

0.1

μV/°C
μV/V

2.5

vs Temperature

Input bias current

mV

±1.25

±7.5

mV

10

40

μV/°C

PSRR

0.5

mV/V

IIN+, IIN-

10

μA

830

kΩ

VBUS input impedance
Input leakage (3)(VIN+ Pin) + (VIN– Pin),
Power-down mode

0.1

Shunt voltage

2.5

μV

Bus voltage

1.25

mV

μA

0.5

DC ACCURACY
ADC native resolution
1 LSB step size

16

Bits

Shunt voltage gain error

0.02

0.1

%

vs Temperature

1050ppm/°CBus voltage gain error

0.02

0.1

%

vs Temperature

1050ppm/°C±0.1

Differential nonlinearity
ADC conversion timeLSB

CT bit = 000

140

154

μs

CT bit = 001

204

224

μs

CT bit = 010

332

365

μs

CT bit = 011

588

646

μs

CT bit = 100

1.1

1.21

ms

CT bit = 101

2.116

2.328

ms

CT bit = 110

4.156

4.572

ms

CT bit = 111

8.244

9.068

ms

28

35

ms

SMBus
SMBus timeout (4)DIGITAL INPUT/OUTPUT
Input capacitance
Leakage input current

30 ≤ VIN ≤ VS

0.1

pF
1

μA

Input logic levels:
VIH

0.7(VS)

6

V

VIL

–0.5

0.3(VS)V

Output logic level
VOL SDA, alert

IOL = 3mA

Hysteresis

(1)
(2)
(3)
(4)

0

0.4
500

V
mV

While the input range is 36V, the full-scale range of the ADC scaling is 40.96V. See the Basic ADC Functions section. Do not apply
more than 36V.
RTI = Referred-to-input.
Input leakage is positive (current flowing into the pin) for the conditions shown at the top of this table. Negative leakage currents canoccur under different input conditions.
SMBus timeout in the INA226 resets the interface any time SCL is low for more than 28ms.

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ELECTRICAL CHARACTERISTICS: VS = +3.3V (continued)
Boldface limits apply over the specified temperature range, TA = –40°C to +125°C.
At TA = +25°C, VIN+ = 12V, VSENSE = (VIN+ – VIN–) = 0mV, VBUS = 12V, unless otherwise noted.
INA226
PARAMETERCONDITIONS

MIN

TYP

MAX

UNIT

POWER SUPPLY
Operating supply range

+5.5

V

Quiescent current

+2.7
330

420

μA

Quiescent current, power-down mode

0.5

2

μA

Power-on reset threshold

2

V

TEMPERATURE RANGE–40

Specified range

+125

°C

THERMAL INFORMATION
INA226
THERMAL METRIC (1)

DGS

UNITS

10 PINS
θJA

Junction-to-ambient thermal resistance

171.4

θJCtopJunction-to-case (top) thermal resistance

42.9

θJB

Junction-to-board thermal resistance

91.8

ψJT

Junction-to-top characterization parameter

1.5

ψJB

Junction-to-board characterization parameter

90.2

θJCbotJunction-to-case (bottom) thermal resistance

n/a

(1)

4

°C/W

For more information about traditional and new thermal metrics, see the IC Package Thermal Metrics application report, SPRA953.

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PIN CONFIGURATIONSDGS PACKAGE
MSOP-10(Top View)
A1

1

10 VIN+

A0

2

9

VIN-

Alert

3

8

VBUS

SDA

4

7

GND

SCL

5

6

VS+

PIN DESCRIPTIONSMSOP-10(DGS)PIN NO

NAME

1

A1

Address pin. Connect to GND, SCL, SDA, or VS. Table 7 shows pin settings and corresponding addresses.

DESCRIPTION

2

A0

Address pin. Connect to GND, SCL, SDA, or VS. Table 7 shows pin settings and corresponding addresses.

3

Alert

Multi-functional alert, open-drain output.

4

SDA

Serial bus data line, open-drain input/output.

5

SCL

Serial bus clock line, open-drain input.

6

VS+

Power supply, 2.7V to 5.5V.

7

GND

Ground.

8

VBUS

Bus voltage input.

9

VIN–

Negative differential shunt voltage. Connect to negative side of shunt resistor.

10

VIN+

Positive differential shunt voltage. Connect to positive side of shunt resistor.

REGISTER BLOCK DIAGRAM
Power

(1)

Bus Voltage(1)´
Current

Shunt Voltage
Channel(1)

ADC

Bus Voltage
ChannelCalibration(2)´
Shunt Voltage(1)

Data Registers(1)

Read-only(2)

Read/write

Figure 1. INA226 Register Block Diagram

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TYPICAL CHARACTERISTICS
At TA = +25°C, VS = +3.3V, VIN+ = 12V, VSENSE = (VIN+ – VIN–) = 0mV, VBUS = 12V, unless otherwise noted.
SHUNT INPUT OFFSET VOLTAGE
PRODUCTION DISTRIBUTIONFREQUENCY RESPONSE
0−10

Population

Gain (dB)

−20
−30
−40

G001

10

8

6

4

Input Offset Voltage (mV)

Figure 2.

Figure 3.

SHUNT INPUT OFFSET VOLTAGE
vs TEMPERATURESHUNT INPUT COMMON-MODE REJECTION RATIOvs TEMPERATURE−1Common−Mode Rejection Ratio (dB)

170

−1.2
−1.4
Offset (µV)

2

100k

0

10k

-2

100
1k
Frequency (Hz)

-4

10

-6

1

-10

−60

-8

−50

−1.6
−1.8
−2
−2.2
−2.4
−50

−25

0

25
50
Temperature (°C)

75

100

160

150

140
−50

125

−25

0

G003

Figure 4.

2550
Temperature (°C)

75

100

125
G004

Figure 5.

SHUNT INPUT GAIN ERROR PRODUCTION DISTRIBUTIONSHUNT INPUT GAIN ERROR vs TEMPERATURE
600

Population

Gain Error (m%)

500
400
300
200

100

80

60

40

20

0

-20

-40

-60

-80

-100

100
0
−50

−25

0

25
50
Temperature (°C)

75

100

125
G007

Input Gain Error (m%)

Figure 6.

6

Figure 7.

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TYPICAL CHARACTERISTICS (continued)
At TA = +25°C, VS = +3.3V, VIN+ = 12V, VSENSE = (VIN+ – VIN–) = 0mV, VBUS = 12V, unless otherwise noted.
SHUNT INPUT GAIN ERROR
vs COMMON-MODE VOLTAGE

BUS INPUT OFFSET VOLTAGE
PRODUCTION DISTRIBUTION

300

200

Population

Gain Error (m%)

250

150
100
50

G008

7.5

6

4.5

3

1.5

36

0

32

-1.5

8
12
16
20
24
28
Common−Mode Input Voltage (V)

-3

4

-4.5

0

-7.5

−50

-6

0

Input Offset Voltage (mV)

Figure 8.

Figure 9.

BUS INPUT OFFSET VOLTAGE vs TEMPERATURE

BUS INPUT GAIN ERROR PRODUCTION DISTRIBUTION−0.6

Population

Offset (mV)

−0.8

−1.0

G009

100

80

60

40

125

20

100

0

75

-20

25
50
Temperature (°C)

-40

0

-60

−25

-100

−1.4
−50

-80

−1.2

Input Gain Error (m%)

Figure 10.

Figure 11.

BUS INPUT GAIN ERROR vs TEMPERATURE

INPUT BIAS CURRENT vs COMMON-MODE VOLTAGE

600

25

Input Bias Current (µA)

Gain Error (m%)

500
400
300
200
100
0
−50

−25

0

25
50
Temperature (°C)

75

100

125

20

15

10

5

0

0

G012

Figure 12.

4

8
12
16
20
24
28
Common−Mode Input Voltage (V)

32

36
G012

Figure 13.

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TYPICAL CHARACTERISTICS (continued)
At TA = +25°C, VS = +3.3V, VIN+ = 12V, VSENSE = (VIN+ – VIN–) = 0mV, VBUS = 12V, unless otherwise noted.
INPUT BIAS CURRENT vs TEMPERATURE

INPUT BIAS CURRENT vs TEMPERATURE, SHUTDOWN
260
Input Bias Current − Shutdown (nA)

Input Bias Current (µA)

24

22

20

18

16
−50

−25

0

25
50
Temperature (°C)

75

100

220
180
140
100
60
20
−50

125

−25

0

G013

Figure 14.
ACTIVE IQ vs TEMPERATURE

100

125
G014

SHUTDOWN IQ vs TEMPERATURE
1.2
Quiescent Current − Shutdown (µA)

Quiescent Current (µA)

75

Figure 15.

500

400

300

200

100
−50

25
50
Temperature (°C)

−25

0

25
50
Temperature (°C)

75

100

1

0.8

0.6

0.4

0.2
−50

125

−25

0

G015

25
50
Temperature (°C)

75

100

125
G016

Figure 16.

Figure 17.

ACTIVE IQ vs I2C CLOCK FREQUENCYSHUTDOWN IQ vs I2C CLOCK FREQUENCY

500

300
250

Shutdown IQ (mA)

IQ (mA)

450

400

200
150
100

350
50
300

0
1

8

10

100

1,000

10,0001

10100Frequency (kHz)Frequency (kHz)

Figure 18.

Figure 19.

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1,000

10,000

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APPLICATION INFORMATIONThe INA226 is a digital current shunt monitor with an I2C- and SMBus-compatible interface. It provides digitalcurrent, voltage, and power readings necessary for accurate decision-making in precisely-controlled systems.
Programmable registers allow flexible configuration for measurement resolution as well as
continuous-versus-triggered operation. Detailed register information appears at the end of this data sheet,
beginning with Table 2. See the Register Block Diagram for a block diagram of the INA226.

INA226 TYPICAL APPLICATION
The front-page figure shows a typical application circuit for the INA226. Use a 0.1μF ceramic capacitor for
power-supply bypassing, placed as closely as possible to the supply and ground pins.

BASIC ADC FUNCTIONSThe INA226 performs two measurements on the power-supply bus of interest. The voltage developed from theload current that flows through a shunt resistor creates a shunt voltage that is measured at the VIN+ and VIN–
pins. The device can also measure the power supply bus voltage by connecting this voltage to the VBUS pin. The
differential shunt voltage is measured with respect to the VIN– pin while the bus voltage is measured withrespect to ground.
The INA226 is typically powered by a separate supply that can range from 2.7V to 5.5V. The bus that is being
monitored can range in voltage from 0V to 36V. It is important to note here that based on the fixed 1.25mV LSB
for the bus voltage register that a full-scale register would result in a 40.96V value. The actual voltage that is
applied to the input pins of the INA226 should not exceed 36V. There are no special considerations for
power-supply sequencing because the common-mode input range and power-supply voltage are independent ofeach other; therefore, the bus voltage can be present with the supply voltage off, and vice-versa.
As noted, the INA226 takes two measurements, shunt voltage and bus voltage. It then converts thesemeasurements to current, based on the Calibration Register value, and then calculates power. Refer to the
Configure/Measure/Calculate Example section for additional information on programming the Calibration
Register.
The INA226 has two operating modes, continuous and triggered, that determine how the ADC operates following
these conversions. When the INA226 is in the normal operating mode (that is, MODE bits of the Configuration
Register are set to '111'), it continuously converts a shunt voltage reading followed by a bus voltage reading.
After the shunt voltage reading, the current value is calculated (based on Equation 3). This current value is thenused to calculate the power result (using Equation 4). These values are subsequently stored in an accumulator,
and the measurement/calculation sequence repeats until the number of averages set in the Configuration
Register is reached. Following every sequence, the present set of values measured and calculated areappended to previously collected values. Once all of the averaging has been completed, the final values forshunt voltage, bus voltage, current, and power are updated in the corresponding registers that can then be read.
These values remain in the data output registers until they are replaced by the next fully completed conversion
results. Reading the data output registers does not affect a conversion in progress.
The Mode control in the Configuration Register also permits selecting modes to convert only the shunt voltage or
the bus voltage in order to further allow the user to configure the monitoring function to fit the specific application
requirements.
All current and power calculations are performed in the background and do not contribute to conversion time.
In triggered mode, writing any of the triggered convert modes into the Configuration Register (that is, MODE bitsof the Configuration Register are set to ‘001’, ‘010’, or ‘011’) triggers a single-shot conversion. This action
produces a single set of measurements; thus, to trigger another single-shot conversion, the Configuration
Register must be written to a second time, even if the mode does not change.
In addition to the two operating modes (continuous and triggered), the INA226 also has a power-down mode that
reduces the quiescent current and turns off current into the INA226 inputs, reducing the impact of supply drain
when the device is not being used. Full recovery from power-down mode requires 40ms. The registers of the
INA226 can be written to and read from while the device is in power-down mode. The device remains in
power-down mode until one of the active modes settings are written into the Configuration Register.

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Although the INA226 can be read at any time, and the data from the last conversion remain available, theConversion Ready Flag bit (Mask/Enable Register, CVRF bit) is provided to help coordinate one-shot or triggered
conversions. The Conversion Ready Flag bit is set after all conversions, averaging, and multiplication operations
are complete.
The Conversion Ready Flag bit clears under these conditions:
1. Writing to the Configuration Register, except when configuring the MODE bits for power-down mode; or
2. Reading the Status Register.
Power Calculation
The Current and Power are calculated following shunt voltage and bus voltage measurements as shown in
Figure 20. Current is calculated following a shunt voltage measurement based on the value set in the Calibration
Register. If there is no value loaded into the Calibration Register, the current value stored is zero. Power iscalculated following the bus voltage measurement based on the previous current calculation and bus voltage
measurement. If there is no value loaded in the Calibration Register, the power value stored is also zero. Again,
these calculations are performed in the background and do not add to the overall conversion time. These current
and power values are considered intermediate results (unless the averaging is set to 1) and are stored in aninternal accumulation register, not the corresponding output registers. Following every measured sample, thenewly-calculated values for current and power are appended to this accumulation register until all of the samples
have been measured and averaged based on the number of averages set in the Configuration Register.
Bus and Power Limit Detect
Following Every Bus Voltage Conversion

Current Limit Detect Following
Every Shunt Voltage Conversion

I

V

I
P

V

I
P

V

I
P

V

I
P

V

I
P

V

I
P

V

I
P

V

I
P

V

I

V

P

I
P

V

I
P

V

I
P

V

I
P

V

I
P

V

I
P

V
P

Power Average

Bus Voltage Average

Shunt Voltage Average

Figure 20. Power Calculation Scheme
In addition to the current and power accumulating after every sample, the shunt and bus voltage measurements
are also collected. Once all of the samples have been measured and the corresponding current and power
calculations have been made, the accumulated average for each of these parameters is then loaded to thecorresponding output registers, where they can then be read.

10

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Averaging and Conversion Time Considerations
The INA226 has programmable conversion times for both the shunt voltage and bus voltage measurements. The
conversion times for these measurements can be selected from as fast as 140μs to as long as 8.244ms. The
conversion time settings, along with the programmable averaging mode, allow the INA226 to be configured to
optimize the available timing requirements in a given application. For example, if a system requires that data beread every 5ms, the INA226 could be configured with the conversion times set to 588μs and the averaging mode
set to 4. This configuration results in the data updating approximately every 4.7ms. The INA226 could also be
configured with a different conversion time setting for the shunt and bus voltage measurements. This type ofapproach is common in applications where the bus voltage tends to be relatively stable. This situation can allow
for the time focused on the bus voltage measurement to be reduced relative to the shunt voltage measurement.
The shunt voltage conversion time could be set to 4.156ms with the bus voltage conversion time set to 588μs,
with the averaging mode set to 1. This configuration also results in data updating approximately every 4.7ms.
There are trade-offs associated with the settings for conversion time and the averaging mode used. The
averaging feature can significantly improve the measurement accuracy by effectively filtering the signal. Thisapproach allows the INA226 to reduce any noise in the measurement that may be caused by noise coupling into
the signal. A greater number of averages enables the INA226 to be more effective in reducing the noise
component of the measurement.
The conversion times selected can also have an impact on the measurement accuracy. This effect can seen in
Figure 21. Multiple conversion times are shown here to illustrate the impact of noise on the measurement. In
order to achieve the highest accuracy measurement possible, a combination of the longest allowable conversion
times and highest number of averages should be used, based on the timing requirements of the system.

10mV/div

Conversion Time: 140ms

Conversion Time: 1.1ms

Conversion Time: 8.244ms

0

200

400

600

800

1000

Number of Conversions

Figure 21. Noise vs Conversion Time

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Filtering and Input Considerations
Measuring current is often noisy, and such noise can be difficult to define. The INA226 offers several options forfiltering by allowing the conversion times and number of averages to be selected independently in the
Configuration Register. The conversion times can be set independently for the shunt voltage and bus voltage
measurements to allow added flexibility in configuring the monitoring of the power-supply bus.
The internal ADC is based on a delta-sigma (ΔΣ) front-end with a 500kHz (±30%) typical sampling rate. Thisarchitecture has good inherent noise rejection; however, transients that occur at or very close to the sampling
rate harmonics can cause problems. Because these signals are at 1MHz and higher, they can be managed byincorporating filtering at the input of the INA226. The high frequency enables the use of low-value series resistors
on the filter with negligible effects on measurement accuracy. In general, filtering the INA226 input is only
necessary if there are transients at exact harmonics of the 500kHz (±30%) sampling rate (greater than 1MHz).
Filter using the lowest possible series resistance (typically 10Ω or less) and a ceramic capacitor. Recommended
values for this capacitor are 0.1μF to 1.0μF. Figure 22 shows the INA226 with an additional filter added at the
input.
Overload conditions are another consideration for the INA226 inputs. The INA226 inputs are specified to tolerate
40V across the inputs. A large differential scenario might be a short to ground on the load side of the shunt. This
type of event can result in full power-supply voltage across the shunt (as long the power supply or energy
storage capacitors support it). Keep in mind that removing a short to ground can result in inductive kickbacks that
could exceed the 40V differential and common-mode rating of the INA226. Inductive kickback voltages are best
controlled by zener-type transient-absorbing devices (commonly called transzorbs) combined with sufficientenergy storage capacitance.
In applications that do not have large energy storage electrolytics on one or both sides of the shunt, an input
overstress condition may result from an excessive dV/dt of the voltage applied to the input. A hard physical shortis the most likely cause of this event, particularly in applications with no large electrolytics present. This problem
occurs because an excessive dV/dt can activate the ESD protection in the INA226 in systems where large
currents are available. Testing has demonstrated that the addition of 10Ω resistors in series with each input of
the INA226 sufficiently protect the inputs against this dV/dt failure up to the 40V rating of the INA226. Selecting
these resistors in the range noted has minimal effect on accuracy.
Power Supply(0V to 36V)

CBYPASS
0.1mF
VS(Supply Voltage)

VBUS

CFILTER
0.1mF to 1mF
Ceramic
Capacitor

SDA
SCL

´
RFILTER£10W

VIN+

Power RegisterV

2

Current Register
ADC
I

Load

RFILTER
£10W

Voltage Register

IC
Interface
Alert
A0

VINAlert Register

A1

GND

Figure 22. INA226 with Input Filtering

12

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ALERT PIN
The INA226 has a single Alert Limit register, 07h, that allows the Alert pin to be programmed to respond to asingle user-defined event or to a conversion ready notification if desired. The Mask/Enable Register allows theuser to select from one of the five available functions to monitor and/or set the conversion ready bit to control the
response of the Alert pin. Based on the function being monitored, the user would then enter a value into the Alert
Limit Register to set the corresponding threshold value that asserts the Alert pin.
The Alert pin allows for one of several available alert functions to be monitored to determine if a user-defined
threshold has been exceeded. The five alert functions that can be monitored are:
•
•
•
•
•

Shunt Voltage Over Limit (SOL)
Shunt Voltage Under Limit (SUL)Bus Voltage Over Limit (BOL)Bus Voltage Under Limit (BUL)Power Over Limit (POL)The Alert pin is an open-drain output. This pin is asserted when the alert function selected in the Mask/Enableregister exceeds the value programmed into the Alert Limit register. Only one of these alert functions can be
enabled and monitored at a time. If multiple alert functions are enabled, the selected function in the highest
significant bit position takes priority and responds to the Alert Limit register value. For example, if the Shunt
Voltage Over Limit and the Shunt Voltage Under Limit are both selected, the Alert pin asserts when the Shunt
Voltage Over Limit Register exceeds the value in the Alert Limit register.
The Conversion Ready state of the device can also be monitored at the Alert pin to inform the user when thedevice has completed the previous conversion and is ready to begin a new conversion. Conversion Ready canbe monitored at the Alert pin along with one of the alert functions. If an alert function and the Conversion Readyare both enabled to be monitored at the Alert pin, after the Alert pin is asserted, the Mask/Enable register must
be read following the alert to determine the source of the alert. By reading the Conversion Ready Flag (CVRF),
bit D3, and the Alert Function Flag (AFF), bit D4 in the Mask/Enable register, the source of the alert can be
determined. If the conversion ready feature is not desired, and the CNVR bit is not set, the Alert pin only
responds to an exceeded alert limit based on the alert function enabled.
If the Alert function is not used, the Alert pin can be left floating without impacting the operation of the device.
Refer to Figure 20 to see the relative timing of when the value in the Alert Limit Register is compared to thecorresponding converted value. For example, if the alert function that is enabled is Shunt Voltage Over Limit(SOL), following every shunt voltage conversion the value in the Alert Limit Register is compared to themeasured shunt voltage to determine if the measurements has exceeded the programmed limit. The AFF, bit 4 of
the Mask/Enable Register, asserts high any time the measured voltage exceeds the value programmed into theAlert Limit Register. In addition to the AFF being asserted, the Alert pin is asserted based on the Alert Polarity Bit(APOL, bit 1 of the Mask/Enable Register). If the Alert Latch is enabled, the AFF and Alert pin remain asserted
until either the Configuration Register is written to or the Mask/Enable Register is read.
The Bus Voltage alert functions compare the measured bus voltage to the Alert Limit Register following every
bus voltage conversion and assert the AFF bit and Alert pins if the limit threshold is exceeded.
The Power Over Limit alert function is also compared to the calculated power value following every bus voltage
measurement conversion and asserts the AFF bit and Alert pins if the limit threshold is exceeded.

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PROGRAMMING THE INA226
An important aspect of the INA226 is that it does not necessarily measure current or power. The INA226
measures both the differential voltage applied between the VIN+ and VIN- input pins and the voltage applied to
the VBUS pin. In order for the INA226 to report both current and power values, the user must program theresolution of the Current Register and the value of the shunt resistor present in the application to develop the
differential voltage applied between the input pins. The Power Register is internally set to be 25 times the
programmed Current_LSB. Both the Current_LSB and shunt resistor value are used in the calculation of theCalibration Register value the INA226 uses to calculate the corresponding current and power values based on
the measured shunt and bus voltages.
The Calibration Register is calculated based on Equation 1. This equation includes the term Current_LSB. This is
the programmed value for the LSB for the Current Register. This is the value the user will use to convert thevalue in the Current Register to the actual current in amps. The highest resolution for the Current Register canbe obtained by using the smallest allowable Current_LSB based on the maximum expected current as shown inEquation 2. While this value will yield the highest resolution, it is common to select a value for the Current_LSB
to the nearest round number above this value to simplify the conversion of the Current Register and Power
Register to amps and watts respectively. The RSHUNT term is the value of the external shunt used to develop
the differential voltage across the input pins. The 0.00512 value in Equation 1 is an internal fixed value used toensure scaling is maintained properly.
0.00512CAL = Current_LSB · R

Current_LSB =

(1)

SHUNT

Maximum Expected Current
215

(2)

Once the Calibration Register has been programmed, the Current Register and Power Register will be updated
accordingly based on the corresponding shunt voltage and bus voltage measurements. Until the Calibration
Register is programmed, the Current and Power Registers remain at zero.

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CONFIGURE/MEASURE/CALCULATE EXAMPLE
In this example, shown in Figure 23, a nominal 10A load creates a differential voltage of 20mV across a 2mΩ
shunt resistor. The bus voltage for the INA226 is measured at the external VBUS input pin, which in this example
is connected to the VIN– pin to measure the voltage level delivered to the load. For this example, the VBUS pin
measures less than 12V because the voltage at the VIN– pin is 11.98V as a result of the voltage drop across theshunt resistor.
+12V Supply

CBYPASS
0.1mF
VS(Supply Voltage)

VBUS

SDA
SCL

´
VIN+

Power RegisterV

2

Current Register
ADC

RSHUNT
2mW

I

Voltage Register

IC
Interface
Alert
A0

VINAlert Register

10A
Load

A1

GND

Figure 23. Example Circuit Configuration
For this example, assuming a maximum expected current of 15A, the Current_LSB is calculated to be
457.7μA/bit using Equation 2. Using a value for the Current_LSB of 500μA/Bit or 1mA/Bit would significantly
simplifiy the conversion from the Current Register and Power Register to amps and watts. For this example, avalue of 1mA/bit was chosen for the current LSB. Using this value for the Current_LSB does trade a small
amount of resolution for having a simpler conversion process on the user side. Using Equation 1 in this example
with a current LSB of 1mA/bit and a shunt resistor of 2mΩ results in a Calibration Register value of 2560, or
A00h.
The Current Register (04h) is then calculated by multiplying the decimal value of the Shunt Voltage Register
contents by the decimal value of the Calibration Register and then dividing by 2048, as shown in Equation 3. For
this example, the Shunt Voltage Register contains a value of 8,000, which is multiplied by the Calibration
Register value of 2560 and then divided by 2048 to yield a decimal value for the Current Register of 10000, or
2710h. Multiplying this value by 1mA/bit results in the original 10A level stated in the example.

Current =ShuntVoltage · CalibrationRegister
2048

(3)

The LSB for the Bus Voltage Register (02h) is a fixed 1.25mV/bit, which means that the 11.98V present at the
VBUS pin results in a register value of 2570h, or a decimal equivalent of 9584. Note that the MSB of the Bus
Voltage Register is always zero because the VBUS pin is only able to measure positive voltages.

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The Power Register (03h) is then be calculated by multiplying the decimal value of the Current Register, 10000,
by the decimal value of the Bus Voltage Register, 9584, and then dividing by 20,000, as defined in Equation 4.
For this example, the result for the Power Register is 12B8h, or a decimal equivalent of 4792. Multiplying thisresult by the power LSB (25 times the [1 × 10–3 Current LSB]) results in a power calculation of (4792 ×
25mW/bit), or 119.82W. The power LSB has a fixed ratio to the current LSB of 25W/bit to 1A/bit. For thisexample, a programmed 1mA/bit current LSB results in a power LSB of 25mW/bit. This ratio is internallyprogrammed to ensure that the scaling of the power calculation is within an acceptable range. A manual
calculation for the power being delivered to the load would use a bus voltage of 11.98V (12VCM – 20mV shuntdrop) multiplied by the load current of 10A to give a result of 119.8W.

Power =

Current · BusVoltage
20,000(4)

Table 1 shows the steps for configuring, measuring, and calculating the values for current and power for thisdevice.
Table 1. Configure/Measure/Calculate Example (1)(1)

STEP #REGISTER NAME

ADDRESSCONTENTSDEC

LSBStep 1

Configuration

00h

4127h

—

—

VALUE
—

Step 2

Shunt

01h

1F40h

8000

2.5µV

20mV

Step 3

Bus

02h

2570h

9584

1.25mV

11.98V

Step 4

Calibration

05h

A00h

2560

—

—

Step 5Current

04h

2710

10000

1mA

10A

Step 6

Power

03h

12B8h

4792

25mW

119.82W

Conditions: Load = 10A, VCM = 12V, RSHUNT = 2mΩ, and VBUS = 12V.

PROGRAMMING THE INA226 POWER MEASUREMENT ENGINE
Calibration Register and Scaling
The Calibration Register makes it possible to set the scaling of the Current and Power Registers to whatevervalues are most useful for a given application. One strategy may be to set the Calibration Register such that thelargest possible number is generated in the Current Register or Power Register at the expected full-scale point.
This approach would yield the highest resolution based using the previously calculated minimum current LSB inthe equation for the Calibration Register. The Calibration Register can also be selected to provide values in the
Current and Power Registers that either provide direct decimal equivalents of the values being measured, or
yield a round LSB value for each corresponding register. After these choices have been made, the Calibration
Register also offers possibilities for end user system-level calibration. By physically measuring the current withan external ammeter, the exact current is known. The value of the Calibration Register can then be adjusted
based on the measured current result of the INA226 to cancel the total system error as shown in Equation 5.

Corrected_Full_Scale_Cal = trunc

Cal ´ MeasShuntCurrent
INA226_Current(5)

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Simple Current Shunt Monitor Usage(No Programming Necessary)
The INA226 can be used without any programming if it is only necessary to read a shunt voltage drop and bus
voltage with the default power-on reset configuration and continuous conversion of shunt and bus voltage.
Without programming the INA226 Calibration Register, the device is unable to provide either a valid current or
power value, because these outputs are both derived using the values loaded into the Calibration Register.

Default INA226 Settings
The default power-up states of the registers are shown in the INA226 Register Descriptions section of this data
sheet. These registers are volatile, and if programmed to a value other than the default values shown in Table 2,
they must be re-programmed at every device power-up. Detailed information on programming the Calibration
Register specifically is given in the Configure/Measure/Calculate Example section and calculated based on
Equation 1.

REGISTER INFORMATIONThe INA226 uses a bank of registers for holding configuration settings, measurement results, minimum/maximum
limits, and status information. Table 2 summarizes the INA226 registers; refer to Figure 1 for an illustration of theregisters.
Table 2. Summary of Register Set
POINTERADDRESS(1)(2)

POWER-ON RESETHEXREGISTER NAMEFUNCTIONBINARYHEXTYPE (1)0

Configuration RegisterAll-register reset, shunt voltage and bus
voltage ADC conversion times andaveraging, operating mode.

01000001 00100111

4127

R/W

1

Shunt Voltage

Shunt voltage measurement data.

00000000 00000000

0000

R

2

Bus Voltage

Bus voltage measurement data.

00000000 00000000

0000

R

3

Power

(2)

Contains the value of the calculated
power being delivered to the load.

00000000 00000000

0000

R

4

Current (2)Contains the value of the calculated
current flowing through the shunt
resistor.

00000000 00000000

0000

R

5

Calibration

Sets full-scale range and LSB of current
and power measurements. Overallsystem calibration.

00000000 00000000

0000

R/W

6

Mask/Enable

Alert configuration and conversion readyflag.

00000000 00000000

0000

R/W

7

Alert Limit

Contains the limit value to compare to
the selected Alert function.

00000000 00000000

0000

R/W

FF

Die ID

ASCII

ASCII

R

Contains unique die identification
number.

Type: R = Read-Only, R/W = Read/Write.
The Current Register defaults to '0' because the Calibration Register defaults to '0', yielding a zero current and power value until the
Calibration Register is programmed.

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REGISTER DETAILSAll 16-bit INA226 registers are two 8-bit bytes via the I2C interface.
Configuration Register 00h (Read/Write)
BIT #

D15

D14

D13

D12

D11

D10

D9

D8

D7

D6

D5

D4

D3

D2

D1

D0

BIT
NAME

RST

—

—

—

AVG2

AVG1

AVG0

VBUSCT2

VBUSCT1

VBUSCT0

VSHCT2

VSHCT1

VSHCT0

MODE3

MODE2

MODE1

POR
VALUE

0

1

0

0

0

0

0

1

0

0

1

0

0

1

1

1

The Configuration Register settings control the operating modes for the INA226. This register controls theconversion time settings for both the shunt and bus voltage measurements as well as the averaging mode used.
The operating mode that controls what signals are selected to be measured is also programmed in the
Configuration Register.
The Configuration Register can be read from at any time without impacting or affecting the device settings or aconversion in progress. Writing to the Configuration Register will halt any conversion in progress until the write
sequence is completed resulting in a new conversion starting based on the new contents of the Configuration
Register. This prevents any uncertainty in the conditions used for the next completed conversion.
Bit Descriptions
RST:

Reset Bit

Bit 15

Setting this bit to '1' generates a system reset that is the same as power-on reset. Resets all registers to default
values; this bit self-clears.

AVG:

Averaging Mode

Bits 9–11

Sets the number of samples that will be collected and averaged together. Table 3 summarizes the AVG bit settings
and related number of averages for each bit.

Table 3. AVG Bit Settings[11:9] (1)

(1)

18

AVG2
D11

AVG1
D10

AVG0
D9

NUMBER OF
AVERAGES

0

0

0

1

0

0

1

4

0

1

0

16

0

1

1

64

1

0

0

128

1

0

1

256

1

1

0

512

1

1

1

1024

Shaded values are default.

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VBUS CT:Bus Voltage Conversion Time

Bits 6–8

Sets the conversion time for the bus voltage measurement. Table 4 shows the VBUS CT bit options and related
conversion times for each bit.

Table 4. VBUS CT Bit Settings [8:6] (1)(1)

VBUS CT2
D8

VBUS CT1
D7

VBUS CT0
D6

CONVERSION TIME

0

0

0

140µs

0

0

1

204µs

0

1

0

332µs

0

1

1

588µs

1

0

0

1.1ms

1

0

1

2.116ms

1

1

0

4.156ms

1

1

1

8.244ms

Shaded values are default.

VSH CT:

Shunt Voltage Conversion Time

Bits 3–5

Sets the conversion time for the shunt voltage measurement. Table 5 shows the VSH CT bit options and related
conversion times for each bit.

Table 5. VSH CT Bit Settings [5:3] (1)(1)

VSH CT2
D5

VSH CT1
D4

VSH CT0
D3

CONVERSION TIME

0

0

0

140µs

0

0

1

204µs

0

1

0

332µs

0

1

1

588µs

1

0

0

1.1ms

1

0

1

2.116ms

1

1

0

4.156ms

1

1

1

8.244ms

Shaded values are default.

MODE:

Operating Mode

Bits 0–2

Selects continuous, triggered, or power-down mode of operation. These bits default to continuous shunt and bus
measurement mode. The mode settings are shown in Table 6.

Table 6. Mode Settings [2:0] (1)

(1)

MODE3
D2

MODE2
D1

MODE1
D0

0

0

0

Power-Down

0

0

1

Shunt Voltage, Triggered

0

1

0

Bus Voltage, Triggered

0

1

1

Shunt and Bus, Triggered

1

0

0

Power-Down

1

0

1

Shunt Voltage, Continuous

1

1

0

Bus Voltage, Continuous

1

1

1

Shunt and Bus, Continuous

MODE

Shaded values are default.

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DATA OUTPUT REGISTERS
Shunt Voltage Register 01h (Read-Only)
The Shunt Voltage Register stores the current shunt voltage reading, VSHUNT. Negative numbers are represented
in twos complement format. Generate the twos complement of a negative number by complementing theabsolute value binary number and adding 1. Extend the sign, denoting a negative number by setting the MSB ='1'.
Example: For a value of VSHUNT = –80mV:
1. Take the absolute value: 80mV
2. Translate this number to a whole decimal number (80mV ÷ 2.5µV) = 32000
3. Convert this number to binary = 111 1101 0000 0000
4. Complement the binary result = 000 0010 1111 1111
5. Add '1' to the complement to create the twos complement result = 000 0011 0000 0000
6. Extend the sign and create the 16-bit word: 1000 0011 0000 0000 = 8300h
If averaging is enabled, this register displays the averaged value. Full-scale range = 81.92mV (decimal = 7FFF);
LSB: 2.5μV.
BIT #

D15

D14

D13

D12

D11

D10

D9

D8

D7

D6

D5

D4

D3

D2

D1

D0

BIT
NAME

SIGN

SD14

SD13

SD12

SD11

SD10

SD9

SD8

SD7

SD6

SD5

SD4

SD3

SD2

SD1

SD0

POR
VALUE

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

Bus Voltage Register 02h (Read-Only) (1)The Bus Voltage Register stores the most recent bus voltage reading, VBUS.
If averaging is enabled, this register displays the averaged value. Full-scale range = 40.96V (decimal = 7FFF);
LSB = 1.25mV.
BIT #

D15

D14

D13

D12

D11

D10

D9

D8

D7

D6

D5

D4

D3

D2

D1

D0

BIT
NAME

—

BD14

BD13

BD12

BD11

BD10

BD9

BD8

BD7

BD6

BD5

BD4

BD3

BD2

BD1

BD0

POR
VALUE

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

(1)

D15 is always zero because bus voltage can only be positive.

Power Register 03h (Read-Only)
If averaging is enabled, this register displays the averaged value.
BIT #

D15

D14

D13

D12

D11

D10

D9

D8

D7

D6

D5

D4

D3

D2

D1

D0

BIT
NAME

PD15

PD14

PD13

PD12

PD11

PD10

PD9

PD8

PD7

PD6

PD5

PD4

PD3

PD2

PD1

PD0

POR
VALUE

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

The Power Register LSB is internally programmed to equal 25 times the programmed value of the Current_LSB.
The Power Register records power in watts by multiplying the decimal values of the current register with thedecimal value of the bus voltage register according to Equation 4.

20

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Current Register 04h (Read-Only)
If averaging is enabled, this register displays the averaged value.
BIT #

D15

D14

D13

D12

D11

D10

D9

D8

D7

D6

D5

D4

D3

D2

D1

D0

BIT
NAME

CSIGN

CD14

CD13

CD12

CD11

CD10

CD9

CD8

CD7

CD6

CD5

CD4

CD3

CD2

CD1

CD0

POR
VALUE

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

The value of the Current Register is calculated by multiplying the decimal value in the Shunt Voltage Registerwith the decimal value of the Calibration Register, according to Equation 3.
Calibration Register 05h (Read/Write)
This register provides the INA226 with the value of the shunt resistor that was present to create the measured
differential voltage. It also sets the resolution of the Current Register. The current LSB and power LSB are set
through the programming of this register. This register is also suitable for use in overall system calibration. See
the Configure/Measure/Calculate Example for additional information on programming the Calibration Register.
BIT #

D15

D14

D13

D12

D11

D10

D9

D8

D7

D6

D5

D4

D3

D2

D1

D0

BIT
NAME

—

FS14

FS13

FS12

FS11

FS10

FS9

FS8

FS7

FS6

FS5

FS4

FS3

FS2

FS1

FS0

POR
VALUE

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

Mask/Enable 06h (Read/Write)
The Mask/Enable Register selects the function that is enabled to control the Alert pin, as well as how that pinfunctions. If multiple functions are enabled, the highest significant bit position Alert Function (D11-D15) takes
priority and responds to the Alert Limit register.
BIT #

D15

D14

D13

D12

D11

D10

D9

D8

D7

D6

D5

D4

D3

D2

D1

D0

BIT
NAME

SOL

SUL

BOL

BUL

POL

CNVR

—

—

—

—

—

AFF

CVRF

OVF

APOL

LEN

POR
VALUE

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

SOL:

Shunt Voltage Over-Voltage

Bit 15

Setting this bit high configures the Alert pin to be asserted when the Shunt Voltage Register exceeds the value in
the Alert Limit Register.

SUL:

Shunt Voltage Under-Voltage

Bit 14

Setting this bit high configures the Alert pin to be asserted when the Shunt Voltage Register drops below the value
in the Alert Limit Register.

BOL:

Bus Voltage Over-Voltage

Bit 13

Setting this bit high configures the Alert pin to be asserted when the Bus Voltage Register exceeds the value in theAlert Limit Register.

BUL:Bus Voltage Under-Voltage

Bit 12

Setting this bit high configures the Alert pin to be asserted when the Bus Voltage Register drops below the value in
the Alert Limit Register.

POL:Over-Limit PowerBit 11

Setting this bit high configures the Alert pin to be asserted when the Power Register exceeds the value in the Alert
Limit Register.

CNVR:

Conversion Ready

Bit 10Setting this bit high configures the Alert pin to be asserted when the Conversion Ready Flag, Bit 3, is asserted
indicating that the device is ready for the next conversion.

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AFF:

Alert Function Flag

Bit 4

While only one Alert Function can be monitored at the Alert pin at a time, the Conversion Ready can also beenabled to assert the Alert pin. Reading the Alert Function Flag following an alert allows the user to determine if theAlert Function was the source of the Alert.
When the Alert Latch Enable bit is set to Latch mode, the Alert Function Flag clears only when the Mask/Enable
Register is read. When the Alert Latch Enable bit is set to Transparent mode, the Alert Function Flag is cleared
following the next conversion that does not result in an Alert condition.

CVRF:

Conversion Ready Flag

Bit 3

Although the INA226 can be read at any time, and the data from the last conversion is available, the Conversion
Ready bit is provided to help coordinate one-shot or triggered conversions. The Conversion bit is set after all
conversions, averaging, and multiplications are complete. Conversion Ready clears under the following conditions:
1.) Writing to the Configuration Register (except for Power-Down or Disable selections)2.) Reading the Mask/Enable Register

OVF:

Math Overflow Flag

Bit 2This bit is set to '1' if an arithmetic operation resulted in an overflow error. It indicates that current and power data
may be invalid.

APOL:

Alert Polarity bit; sets the Alert pin polarity.

Bit 1

1 = Inverted (active-high open collector)
0 = Normal (active-low open collector) (default)

LEN:

Alert Latch Enable; configures the latching feature of the Alert pin and Flag bits.

Bit 0

1 = Latch enabled
0 = Transparent (default)
When the Alert Latch Enable bit is set to Transparent mode, the Alert pin and Flag bits will reset to their idle states
when the fault has been cleared. When the Alert Latch Enable bit is set to Latch mode, the Alert pin and Flag bits
will remain active following a fault until the Mask/Enable Register has been read.

Alert Limit 07h (Read/Write)
The Alert Limit Register contains the value used to compare to the register selected in the Mask/Enable Registerto determine if a limit has been exceeded.
BIT #

D15

D14

D13

D12

D11

D10

D9

D8

D7

D6

D5

D4

D3

D2

D1

D0

BIT
NAME

AUL15

AUL14

AUL13

AUL12

AUL11

AUL10

AUL9

AUL8

AUL7

AUL6

AUL5

AUL4

AUL3

AUL2

AUL1

AUL0

POR
VALUE

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

BUS OVERVIEWThe INA226 offers compatibility with both I2C and SMBus interfaces. The I2C and SMBus protocols are
essentially compatible with one another.
The I2C interface is used throughout this data sheet as the primary example, with SMBus protocol specified only
when a difference between the two systems is discussed. Two bidirectional lines, SCL and SDA, connect the
INA226 to the bus. Both SCL and SDA are open-drain connections.
The device that initiates a data transfer is called a master, and the devices controlled by the master are slaves.
The bus must be controlled by a master device that generates the serial clock (SCL), controls the bus access,and generates START and STOP conditions.
To address a specific device, the master initiates a start condition by pulling the data signal line (SDA) from ahigh to a low logic level while SCL is high. All slaves on the bus shift in the slave address byte on the rising edgeof SCL, with the last bit indicating whether a read or write operation is intended. During the ninth clock pulse, theslave being addressed responds to the master by generating an Acknowledge and pulling SDA low.

22

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Data transfer is then initiated and eight bits of data are sent, followed by an Acknowledge bit. During datatransfer, SDA must remain stable while SCL is high. Any change in SDA while SCL is high is interpreted as astart or stop condition.
Once all data have been transferred, the master generates a stop condition, indicated by pulling SDA from low tohigh while SCL is high. The INA226 includes a 28ms timeout on its interface to prevent locking up the bus.
Serial Bus Address
To communicate with the INA226, the master must first address slave devices via a slave address byte. The
slave address byte consists of seven address bits and a direction bit that indicates whether the action is to be aread or write operation.
The INA226 has two address pins, A0 and A1. Table 7 describes the pin logic levels for each of the 16 possible
addresses. The state of pins A0 and A1 is sampled on every bus communication and should be set before any
activity on the interface occurs.
Table 7. INA226 Address Pins andSlave Addresses
A1

A0

SLAVE ADDRESS

GND

GND

1000000

GND

VS+

1000001

GND

SDA

1000010GND

SCL

1000011VS+

GND

1000100

VS+

VS+

1000101

VS+

SDA

1000110VS+

SCL

1000111SDA

GND

1001000

SDA

VS+

1001001

SDA

SDA

1001010SDA

SCL

1001011SCL

GND

1001100

SCL

VS+

1001101

SCL

SDA

1001110SCL

SCL1001111

Serial Interface
The INA226 operates only as a slave device on both the I2C bus and the SMBus. Connections to the bus are
made via the open-drain I/O lines SDA and SCL. The SDA and SCL pins feature integrated spike suppression
filters and Schmitt triggers to minimize the effects of input spikes and bus noise. While there is spike suppression
integrated into the digital I/O lines, proper layout should be used to minimize the amount of coupling into thecommunication lines. This noise introduction could occur from capacitively coupling signal edges between thetwo communication lines themselves or from other switching noise sources present in the system. Routing tracesin parallel with ground in between layers on a printed circuit board (PCB) typically reduces the effects of coupling
between the communication lines. Shielding communication lines in general is recommended to reduce topossibility of unintended noise coupling into the digital I/O lines that could be incorrectly interpreted as start orstop commands.
The INA226 supports the transmission protocol for Fast (1kHz to 400kHz) and High-speed (1kHz to 3.4MHz)
modes. All data bytes are transmitted most significant byte first.

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WRITING TO/READING FROM THE INA226
Accessing a specific register on the INA226 is accomplished by writing the appropriate value to the register
pointer. Refer to Table 2 for a complete list of registers and corresponding addresses. The value for the register
pointer (as shown in Figure 27) is the first byte transferred after the slave address byte with the R/W bit low.
Every write operation to the INA226 requires a value for the register pointer.
Writing to a register begins with the first byte transmitted by the master. This byte is the slave address, with theR/W bit low. The INA226 then acknowledges receipt of a valid address. The next byte transmitted by the masteris the address of the register which data will be written to. This register address value updates the register
pointer to the desired register. The next two bytes are written to the register addressed by the register pointer.
The INA226 acknowledges receipt of each data byte. The master may terminate data transfer by generating astart or stop condition.
When reading from the INA226, the last value stored in the register pointer by a write operation determines
which register is read during a read operation. To change the register pointer for a read operation, a new value
must be written to the register pointer. This write is accomplished by issuing a slave address byte with the R/W
bit low, followed by the register pointer byte. No additional data are required. The master then generates a start
condition and sends the slave address byte with the R/W bit high to initiate the read command. The next byte istransmitted by the slave and is the most significant byte of the register indicated by the register pointer. This byte
is followed by an Acknowledge from the master; then the slave transmits the least significant byte. The masteracknowledges receipt of the data byte. The master may terminate data transfer by generating a
Not-Acknowledge after receiving any data byte, or generating a start or stop condition. If repeated reads from thesame register are desired, it is not necessary to continually send the register pointer bytes; the INA226 retains
the register pointer value until it is changed by the next write operation.
Figure 24 and Figure 25 show the write and read operation timing diagrams, respectively. Note that register
bytes are sent most-significant byte first, followed by the least significant byte.
1

9

9

1

9

1

9

1

SCL

SDA

1

0

0

A3

A2

A1

A0

R/W

Start By
Master

P7

P6

P5

P4

P3

P2

P1

ACK ByINA226
Frame 1 Two-Wire Slave Address Byte

(1)

P0

D15 D14D13

D12 D11 D10

D9

D8

(1)

D7

D6

D5

D4

D3

D2

D1

D0

ACK ByINA226ACK ByINA226
Frame 2 Register Pointer Byte

ACK ByINA226

Frame 3 Data MSByte

Stop By
MasterFrame 4 Data LSByte

The value of the Slave Address byte is determined by the settings of the A0 and A1 pins. Refer to Table 7.

Figure 24. Timing Diagram for Write Word Format
1

9

1

9

1

9

SCL

SDA

1

0

0

A3

A2

A1

A0

R/W

Start By
Master

D15 D14
ACK ByINA226

Frame 1 Two-Wire Slave Address Byte

(1)

D13

D12

D11 D10

D9

D8

From
INA226
Frame 2 Data MSByte

D7

D6

D5

D4

D3

D2

D1

From
INA226ACK ByMaster

(2)

Frame 3 Data LSByte

D0
No ACK By
Master

(3)

Stop

(2)

(1)

The value of the Slave Address byte is determined by the settings of the A0 and A1 pins. Refer to Table 7.

(2)

Read data is from the last register pointer location. If a new register is desired, the register pointer must be updated.
See Figure 23.

(3)

ACK by Master can also be sent.

Figure 25. Timing Diagram for Read Word Format

24

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Figure 26 shows the timing diagram for the SMBus Alert response operation. Figure 27 illustrates a typicalregister pointer configuration.
ALERT
1

9

1

9

SCL

SDA

0

0

0

1

1

0

0

R/W

Start By
Master

1

0

0

A2

ACK ByINA226

A1

A0

0

From
INA226

Frame 1 SMBus ALERT Response Address Byte

(1)

A3

Frame 2 Slave Address Byte

NACK By
MasterStop By
Master(1)

The value of the Slave Address Byte is determined by the settings of the A0 and A1 pins. Refer to Table 7.

Figure 26. Timing Diagram for SMBus ALERT
1

9

1

9

SCL

¼

SDA

1

0

0

A3

A2

A1

A0

R/W

Start By
MasterFrame 1 Two-Wire Slave Address Byte

(1)

P7

P6

P5

P4

P3

P2

P1

ACK ByINA226
(1)

P0

Stop

ACK ByINA226
Frame 2 Register Pointer Byte

The value of the Slave Address Byte is determined by the settings of the A0 and A1 pins. Refer to Table 7.

Figure 27. Typical Register Pointer Set

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High-Speed I2C Mode
When the bus is idle, both the SDA and SCL lines are pulled high by the pull-up devices. The master generates
a start condition followed by a valid serial byte containing High-Speed (HS) master code 00001XXX. Thistransmission is made in fast (400kHz) or standard (100kHz) (F/S) mode at no more than 400kHz. The INA226
does not acknowledge the HS master code, but does recognize it and switches its internal filters to support
3.4MHz operation.
The master then generates a repeated start condition (a repeated start condition has the same timing as the start
condition). After this repeated start condition, the protocol is the same as F/S mode, except that transmission
speeds up to 3.4MHz are allowed. Instead of using a stop condition, repeated start conditions should be used tosecure the bus in HS-mode. A stop condition ends the HS-mode and switches all the internal filters of the
INA226 to support the F/S mode.
t(LOW)tF

tR

t(HDSTA)SCLt(HDSTA)t(HIGH)t(SUSTO)t(SUSTA)t(HDDAT)t(SUDAT)SDAt(BUF)PSS

P

Figure 28. Bus Timing Diagram
Bus Timing Diagram Definitions
FAST MODE
PARAMETERHIGH-SPEED MODE

MIN

MAX

MIN

MAX

UNITS

SCL operating frequencyf(SCL)

0.001

0.4

0.001

3.4

MHz

Bus free time between stop and start
conditions

t(BUF)

600

160

ns

Hold time after repeated START condition.
After this period, the first clock is generated.

t(HDSTA)

100

100

ns

Repeated start condition setup timet(SUSTA)

100

100

ns

STOP condition setup timet(SUSTO)

100

100

ns

Data hold timet(HDDAT)00ns

Data setup timet(SUDAT)

100

10

ns

SCL clock low periodt(LOW)

1300

160

ns

SCL clock high periodt(HIGH)

600

60

Clock/data fall timetF

Clock/data rise time
Clock/data rise time for SCLK ≤ 100kHz

26

ns

300

160

ns

tR

300

160

ns

tR

1000

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SMBus Alert Response
The INA226 is designed to respond to the SMBus Alert Response address. The SMBus Alert Response provides
a quick fault identification for simple slave devices. When an Alert occurs, the master can broadcast the Alert
Response slave address (0001 100) with the Read/Write bit set high. Following this Alert Response, any slave
devices that generated an alert will identify themselves by acknowledging the Alert Response and sending theirrespective address on the bus.
The Alert Response can activate several different slave devices simultaneously, similar to the I2C General Call. If
more than one slave attempts to respond, bus arbitration rules apply. The losing device does not generate an
Acknowledge and continues to hold the Alert line low until the interrupt is cleared.

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PACKAGE OPTION ADDENDUM

www.ti.com

13-Jul-2011

PACKAGING INFORMATION
Orderable Device

Status(1)

Package Type Package
Drawing

INA226AIDGSR

ACTIVEMSOP

INA226AIDGSTACTIVE

MSOP

Pins

Package Qty

Eco Plan

(2)

Lead/
Ball Finish

DGS

10

2500

Green (RoHS& no Sb/Br)

CU NIPDAUAGLevel-2-260C-1 YEAR

DGS

10

250

Green (RoHS& no Sb/Br)

CU NIPDAUAGLevel-2-260C-1 YEARMSL Peak Temp

(3)

Samples(Requires Login)(1)

The marketing status values are defined as follows:
ACTIVE: Product device recommended for new designs.
LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.
NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.
PREVIEW: Device has been announced but is not in production. Samples may or may not be available.
OBSOLETE: TI has discontinued the production of the device.
(2)

Eco Plan - The planned eco-friendly classification: Pb-Free (RoHS), Pb-Free (RoHS Exempt), or Green (RoHS & no Sb/Br) - please check http://www.ti.com/productcontent for the latest availability
information and additional product content details.
TBD: The Pb-Free/Green conversion plan has not been defined.
Pb-Free (RoHS): TI's terms "Lead-Free" or "Pb-Free" mean semiconductor products that are compatible with the current RoHS requirements for all 6 substances, including the requirement thatlead not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, TI Pb-Free products are suitable for use in specified lead-free processes.
Pb-Free (RoHS Exempt): This component has a RoHS exemption for either 1) lead-based flip-chip solder bumps used between the die and package, or 2) lead-based die adhesive used between
the die and leadframe. The component is otherwise considered Pb-Free (RoHS compatible) as defined above.
Green (RoHS & no Sb/Br): TI defines "Green" to mean Pb-Free (RoHS compatible), and free of Bromine (Br) and Antimony (Sb) based flame retardants (Br or Sb do not exceed 0.1% by weightin homogeneous material)(3)

MSL, Peak Temp. -- The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature.

Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is provided. TI bases its knowledge and belief on information
provided by third parties, and makes no representation or warranty as to the accuracy of such information. Efforts are underway to better integrate information from third parties. TI has taken andcontinues to take reasonable steps to provide representative and accurate information but may not have conducted destructive testing or chemical analysis on incoming materials and chemicals.
TI and TI suppliers consider certain information to be proprietary, and thus CAS numbers and other limited information may not be available for release.
In no event shall TI's liability arising out of such information exceed the total purchase price of the TI part(s) at issue in this document sold by TI to Customer on an annual basis.

Addendum-Page 1

PACKAGE MATERIALS INFORMATION
www.ti.com

31-Aug-2011

TAPE AND REEL INFORMATION*All dimensions are nominal

DevicePackage Package Pins
Type Drawing

SPQ

Reel
Reel
A0
Diameter Width (mm)(mm) W1 (mm)INA226AIDGSR

MSOP

DGS

10

2500

330.0

12.4

INA226AIDGST

MSOP

DGS

10

250

330.0

12.4

Pack Materials-Page 1

B0
(mm)

K0
(mm)

P1
(mm)

W
Pin1
(mm) Quadrant

5.3

3.4

1.4

8.0

12.0

Q1

5.3

3.4

1.4

8.0

12.0

Q1

PACKAGE MATERIALS INFORMATION
www.ti.com

31-Aug-2011*All dimensions are nominal

DevicePackage Type

Package Drawing

Pins

SPQ

Length (mm)Width (mm)Height (mm)INA226AIDGSR

MSOP

DGS

10

2500

366.0

364.0

50.0

INA226AIDGST

MSOP

DGS

10

250

366.0

364.0

50.0

Pack Materials-Page 2

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