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Application Report

Basics of Power MUXAlex Triano
ABSTRACTA Power Multiplexer (Power MUX) is a set of electronic switches used to select and transition between two or
more input power paths to a single output. A system targeting flexibility to choose between different styles of
input power (barrel-jack, USB cable, wireless charging) may need a simple set of switches and logic to select thedesired path to enable. In comparison, a system using a backup power supply may rely on critical operation anddata transmission which must be maintained. These applications may require a fast or seamless switchover
response to ensure the system does not reset during any power transitions.
Since most Power MUX solutions are used to manage input power paths, they are a good candidate to integrate
additional protection features against overvoltage or overcurrent faults. This application note explores each of
the different topologies of Power MUX solutions, different switchover behavior and what protection features areavailable.
Table 1-1. Power MUX Selection Guide
Integration

Voltage

Max Current

Control Method

Switchover Method

3A
Fully Integrated

2.8 V - 22 V

Switchover Time

Protection Features

100 usAutomatic + Manual

4A

5 us

Overvoltage +Overcurrent

Break-before-make

Sugg.
DeviceWhen to use

TPS2120

Small solution sizewith protection.

TPS2121

Small solution sizewith fast switchoverand protection.

1.4 V - 5.5 V

2A

Manual

20 us(1)None

TPS22910 +TPS22912

Low voltage without
protection.

0.7 V - 5.7 V

5AAutomatic

n/a

None

TPS22954

Low voltage with
output power cycle
during switchover.

TPS25942

Instantaneous
switchover prevents
output from dropping
more than 0.7 V
below lowest supply.

TPS25947

Low on-resistance,
fast switchover withtrue reverse current
blocking and input
reverse polarity
protection.

n/a

TPS24740

High power
applications.

2.7 V - 18 V

5A

Automatic

Semi-Integratedn/a

Diode-Mode
2.7 V - 23 V

5.5 A

Automatic

30 us
Overvoltage +Overcurrent(1)

2.5 A - 18 V

Ext. FET

Automatic

4.2 V - 55 V

2A

Automatic

Break-before-make

200 us(1)TPS2660xHigh voltage
applications withprotection.

–80 V - –10 V

Ext. FET

Automatic

Diode-Moden/a

TPS23523

Negative voltage
applications.

Based on test results from Power Multiplexing Using Load Switches and eFuses

Table of Contents
1 What is a Priority Power MUX?..............................................................................................................................................2
2 Control Method....................................................................................................................................................................... 33 Power MUX Topologies.......................................................................................................................................................... 6
4 Switchover Method.................................................................................................................................................................95 Additional Protection............................................................................................................................................................12
6 Summary............................................................................................................................................................................... 12
7 References............................................................................................................................................................................ 12

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Trademarks

8 Revision History................................................................................................................................................................... 12

List of Figures
Figure 1-1. Power MUX Block Diagram.......................................................................................................................................2
Figure 1-2. Minimum Functionality for Power MUX Without Priority............................................................................................3
Figure 1-3. Example Priority Power MUX.................................................................................................................................... 3
Figure 2-1. Manual Power MUX using TPS22910 and TPS22912 Load Switches..................................................................... 4
Figure 2-2. Automatic Power MUX using 2x TPS259470x eFuses............................................................................................. 5
Figure 2-3. Automatic Power MUX with Manual Override using TPS2120..................................................................................6
Figure 3-1. Manual and Automatic Discrete Power MUX with Priority.........................................................................................6
Figure 3-2. Load Switch with Parasitic Body Diode Removed.....................................................................................................7
Figure 3-3. Semi-Integrated Power MUX using TPS22910 and TPS22912 Load Switches........................................................7
Figure 3-4. Semi-Integrated Power MUX using 2x TPS2660 eFuses......................................................................................... 8
Figure 3-5. Fully-Integrated Priority Power MUX with TPS2120..................................................................................................9
Figure 4-1. Voltage Dip on Output During Switchover Time...................................................................................................... 10
Figure 4-2. Inrush Current Spike Caused by Supply Switchover...............................................................................................10
Figure 4-3. Inrush Current Spike on IN2 During Switchover Using 2x TPS25942..................................................................... 11

List of Tables
Table 1-1. Power MUX Selection Guide...................................................................................................................................... 1

Trademarks
All other trademarks are the property of their respective owners.

1 What is a Priority Power MUX?
A basic Power Multiplexer (Power MUX) selects between two or more input supplies to power a single output.

Figure 1-1. Power MUX Block Diagram
If there is no preference for which input supply to use, or if the preference is to always use the highest input
voltage supply available, then the minimum requirement for a power MUX solution would be reverse current
blocking for each input path. This can be accomplished using any combination of diodes or ICs which behave
like a diode (such as Ideal Diode Controllers).

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Figure 1-2. Minimum Functionality for Power MUX Without Priority
A schottky or silicon diode will result in a voltage drop around 0.4 V or 0.7 V, respectively. Using an ideal diodecontroller will result in a much lower voltage drop (on the order of 10 mV to 100 mV and there will be a parasitic
body diode which must be positioned to block reverse current when the switch detects reverse current or isdisabled.
If there is a priority, then additional switches must be added to have full control over which path to enable.
Reverse current blocking (through a diode or a FET) must remain present and now a MOSFET must be added toturn on/off each power path to the load.

Figure 1-3. Example Priority Power MUXThe focus of this application note will be on priority power MUX solutions and how they can be implemented.

2 Control Method
Power MUX solutions need a way to determine which input supply should provide power to the output. There are
generally three options available on the market: Manual, Automatic, or Both.

2.1 Manual
A manual power MUX is one in which each path is individually controlled by an external signal (logic or
microcontroller). The example of two load switches used in Figure 2-1 is a manual power MUX. There could be
one or two EN pins which need to be controlled. This method is generally used when there is already amicrocontroller present in the system which can decide under what conditions to enable each input.

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Figure 2-1. Manual Power MUX using TPS22910 and TPS22912 Load Switches

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2.2 Automatic
An automatic power MUX does not require an external signal to switch between loads. There is often a default
priority (such as IN1) and the device will determine under what conditions to switch to IN2. The first condition will
be when IN1 drops below a certain threshold (such as if IN1 is removed and the voltage decays). There could beother conditions such as during an overvoltage event on IN1, where the supply may switch to IN2 to power theload. This control method is commonly used when there is no microcontroller available or to simplify the design
architecture and eliminate the need to rely on the microcontroller's resources. Note that most automatic power
MUX solutions can be used in automatic mode or manual mode but not both.

VIN1

IN

VOUT

OUT

VLOGIC
EN/UVLO

COUT
TPS259470x

FLT
OVLO
AUXOFF

VIN2

IN

OUT

VLOGIC
EN/UVLO
TPS259470x
FLT
AUXOFF
OVLO
Figure 2-2. Automatic Power MUX using 2x TPS259470x eFuses

2.3 Both - Automatic + Manual Override
There are some Power MUX solutions which offer the flexibility to be used in a automatic configuration and becontrolled by a manual control signal. The TPS212x family of Power MUX solutions can have a default(automatic) priority, but then be overriden by an external microcontroller if needed. This method is useful in

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Power MUX Topologies

applications which will have a default priority for most of its operation, but there will be some modes (such as
diagnostics) requiring manual control to force which path is enabled.

Figure 2-3. Automatic Power MUX with Manual Override using TPS2120

3 Power MUX Topologies
3.1 Discrete
A 2-input priority Power MUX solution can be implemented using 4x discrete MOSFETs (2x paths of back-backFETs) along with manual or automatic logic to determine which path to enable. PMOS based solutions arecommonly used when there is no higher voltage source or charge pump available (otherwise an NMOS-basedarchitecture would be advantageous).

Figure 3-1. Manual and Automatic Discrete Power MUX with Priority
In this example, the manual power MUX can be controlled with two EN pins tied to a microcontroller. The
microcontroller would need logic to ensure only one set of switches is on at a time, to prevent reverse current
flow. The automatic MUX features a comparator followed by inverter logic to ensure only one set of switches isturned on at a time. The comparator is configured to turn on the top set of switches when input 1 is present,
otherwise default to input 2 when present.

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Power MUX Topologies

3.2 Semi-Integrated
For low-voltage inputs (less than 5 V), there are load switches available with a single integrated MOSFET but
have the ability to block reverse current when disabled. These switches can accomplish this by effectively
removing the body diode of the integrated FET while the switch is disabled.

Figure 3-2. Load Switch with Parasitic Body Diode Removed
If using one of these load switches with an active high enable and another load switch with active low enable,
you can select between each power path while using only 1x GPIO.

Figure 3-3. Semi-Integrated Power MUX using TPS22910 and TPS22912 Load Switches
For higher input voltages (> 5 V), there are eFuse switches available with back-back MOSFETs. They can beused in a priority mux configuration (see Figure 3-4).

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TPS26600

VIN1
19 V to 28.8 V

VOUT

C1

IN

OUT

UVLO

SHDN

R1
715k

1 µF

C3
220 µF

R2
20k
OVP

R3
30.1k
C2
22 nF

FLT

dVdT

IMON

MODE

LIM

RTN

PWP

R4
12.1k

GND

TPS26600

VIN2
19 V to 28.8 V

C1

IN

OUT

UVLO

SHDN

R1
715k

1 µF
R2
20k

OVP
DMN62D0U-7

R5
100k

R3
30.1k
C2
22 nF

FLT

dVdT

IMON

MODE

LIM

RTN

PWP

R4
12.1k

GND

Figure 3-4. Semi-Integrated Power MUX using 2x TPS2660 eFuses
To learn more about how to use load switches or eFuses in a MUX configuration, see Power Multiplexing Using
Load Switches and eFuses.

3.3 Fully Integrated
TI’s portfolio of fully-integrated Power MUXes contains all 4x MOSFETs and switching logic in a single IC. These
solutions provide all the functionality needed for a priority power mux in the smallest solution size possible.
Additional features such as output status, slew rate control, overvoltage and overcurrent protection are included
in devices such as the TPS212x family.

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Figure 3-5. Fully-Integrated Priority Power MUX with TPS2120

4 Switchover Method
When a power MUX solution transitions powering the output from one supply to the other supply, this is referred
to as the switchover event. The method a power MUX uses to perform the switchover will affect how muchreverse current is conducted and how much the output voltage will dip.

4.1 Break-Before-Make vs. Diode Mode
There are two sets of switchover methods that power MUX solutions fall under:
1. Break-before-make method occurs when the switch for the first supply completely turns off before thesecond supply switch is turned on.
a. This prevents reverse current flow from one supply to another.
b. There is a period of time where no power is being delivered from the supply to the output. This is known
as the switchover time, or tSW.
2. Diode mode is a make-before-break method where the diode or switch for the first supply remains on while
the second supply switch is turned on. Reverse current is then prevented by the presence of a diode or a
device which detects the reverse current flow and shuts off a corresponding FET (such as our eFuse, Ideal
Diode or ORing controllers).
a. The benefit of this approach is minimal output voltage drop, as power is continuously supplied to the load.
b. The tradeoff depends on what diode device is used:i. Schottky or Silicon diode will result in power dissipation and voltage drop during normal operation.
ii. eFuse, ORing or Ideal diode controller methods will result in some level of reverse current flow,
potentially significant or insignificant depending on the application.

4.2 What is Seamless Switchover?
When switching between one supply to another, there are two possible outcomes:
1. The output voltage drops below operating range, causing the loads to experience a systematic reset.
2. The output voltage remains within operating range, causing uninterrupted operation. We will classify this typeof outcome as seamless switchover.

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If using a break-before-make power MUX, then switchover time is one key factor which will determine whether aseamless switchover will or will not occur. Faster switchover time will help achieve seamless switchover, at theexpense of higher inrush current. This balance should be considered and power MUX solutions are available
with a range of switchover times.
If using a diode-mode or make-before-break power MUX, then seamless switchover is often possible since
worst-case output voltage drop will be approximately 0.4 V to 0.7 V (depending on the diode used).

4.3 Output Voltage Drop
With a break-before-make power mux, there will be a period of time (tSW , switchover time) where the input
supply is not providing power to the output. This will cause the output voltage to decay based on the following
equations:Figure 4-1. Voltage Dip on Output During Switchover TimeVO U T , M I N = VS W - VD I P(1)VD I P = tS W × ( IO U T / CO U T )(2)Therefore a faster switchover time, tSW will result in a smaller voltage dip on the output, VDIP.

4.4 Inrush Current
A faster slew rate switch will reduce the switchover time, but will cause a faster dVOUT/dt and therefore a larger
spike of inrush current based on the equation:
II N R U S H = CO U T ×

d VO U T(3)

dt

Figure 4-2. Inrush Current Spike Caused by Supply Switchover

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Figure 4-3. Inrush Current Spike on IN2 During Switchover Using 2x TPS25942
In this example, 2x TPS25942 eFuses were used to form a semi-integrated power MUX solution. The device
was initially powered by CH-1, I_IN and then transitioned to CH-2, I_IN2. During the switchover time, output
voltage began to drop by a diode drop. Once the switchover passed, there was a peak inrush current spike ofapproximately 3.42 A in order for the output to recharge. More examples of peak inrush current test results canbe found at Power Multiplexing Using Load Switches and eFuses.
There are two variables that can help a designer meet their target output voltage dip versus inrush current
performance in a power MUX solution.
1. Output Capacitance - Following equations 1 through 4, increasing COUT will cause lower output voltage dip at
the expense of higher inrush current during the transition, and vice-versa.
2. Switchover Times - Discrete power MUX solutions rely on RC delays in order to limit inrush current. This will
result in relatively slow switchover times and relatively high dv/dt as the switch rise time will get exponentiallylarger as it turns on. In comparison, semi-integrated and fully integrated power MUX solutions often use acontrolled linear rise time. This will result in relatively lower amounts of inrush current and a faster switchover
time. There will be integrated power MUX solutions available at slew rate and switchover time combinations
which are simply not possible with a discrete solution.

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5 Additional Protection
Since power MUX solutions are often used at the input to a system, it is a good location to integrate protection
features such as overvoltage or overcurrent protection.

5.1 Overvoltage Protection
Some applications need to protect against undesired high-voltage DC supplies or against transient induced
voltages (such as from surge events or inductive switching). These potentially harmful voltages can be blockedfrom downstream components by using a power MUX with protection.

5.2 Overcurrent Protection
If a downstream circuit or fault event begins to draw excessive amounts of current, it is essential to limit thatcurrent quickly to avoid potential circuit damage or fire. This is another level of protection that can be integrated
within a power mux.
TI provides power mux solutions with both overvoltage and overcurrent protection. For example, 2x TPS2660 or
2x TPS25947 are semi-integrated power MUX solutions and TPS212x is a fully-integrated power MUX which
each offer this level of protection.

6 Summary
There are different power MUX control methods, topologies, and switchover methods which offer a certain levelof flexibility, protection and performance. System concerns such as output voltage drop or inrush current can beaddressed by utilizing Texas Instruments' portfolio of semi-integrated Load Switch and eFuse solutions, or a
fully-integrated Power MUX such as the TPS212x family which can offer the highest level of functionality in thesmallest size available.

7 References•••

Seamless Switchover for Backup Power Reference Design
Power Multiplexing Using Load Switches and eFuses
Basics of eFuses

8 Revision History
NOTE: Page numbers for previous revisions may differ from page numbers in the current version.
Changes from Revision * (November 2018) to Revision A (October 2020)
Page• Updated the numbering format for tables, figures and cross-references throughout the document...................2

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