Basics of Power Switches

A Power Switch provides an electrical connection from a voltage source or ground to a load. It saves power across multiple voltage rails and protects subsystems from damage. It also provides enhanced component protection, inrush current protection, and minimizes printed-circuit board (PCB) size.

There are several power switch topologies with different functions that address different applications. Load Switches establish the power switch foundation by providing safe and reliable distribution of power. Applications typically using load switches include power distribution, power sequencing, inrush current control, and reduced current leakage. Integrated Power MUX devices are similar to load switches but allow for multiple input sources. This set of electronic switches is used to select and transition between two or more input power paths to a single output while also providing input power protection.

eFuses and Hot Swap controllers provide additional input power path protection functions such as current sense monitoring, current limiting, undervoltage and overvoltage protection, and thermal shutdown. This makes these devices ideal for hot-plug and transient events that would otherwise damage system components. These benefits help reduce system maintenance costs and maximize equipment uptime.

Ideal diode, ORing controllers provide protection against reverse-polarity conditions by monitoring an external FET, significantly reducing power loss, and blocking reverse current. Whenever a transient event occurs, the controller monitors and adjusts the external FET to prevent damage to upstream components.

Smart high-side switches are for off-board load protection. They provide additional diagnostic telemetry that monitors the output load current and detects short-circuit and open-load events. Smart high-side switches have adjustable current limits, allowing for more reliable integration into applications with either large inrush current startup profiles or low peak currents. Adding a smart high-side switch to a design leads to a smarter and more robust solution for driving capacitive, inductive, and LED loads.

Low-side switches connect the load to ground instead of providing a connection between a power supply and the load. By including an integrated flyback diode, low-side switches help eliminate inductive load transients by dissipating current in a circular loop. This allows them to drive inductive loads such as solenoids, relays, and motors.

This application report highlights the different topologies within the power switch portfolio, and provides suggestions in choosing the correct solution for a faster design time.

Table 1. Power Switch Topology Table

	POWER DISTRIBUTION		POWER PATH PROTECTION
	Load Switch	Power MUX (2 input, 1 output)	eFuse (Internal FET)	Hot Swap (External FET)	Ideal Diode ORing Controller	Smart High-Side Switch	Low-Side Switch
Voltage Range	0 V to 18 V	2.8 V to 22 V	2.7 V to 60 V	±80 V	±75 V	6 V to 40 V	0 V to 100 V
Max Operating Current	15 A	4.5 A	15 A	N/A	N/A	12 A	1 A
Functions
Inrush Current Control	✓	✓	✓	✓		✓
Adjustable Current Limit		✓	✓	✓		✓
Reverse Current Blocking	✓	✓	✓	✓	✓
Current Sense Monitoring			✓	✓		✓
Short-Circuit Protection	✓⁽¹⁾	✓	✓	✓		✓
Overvoltage Protection		✓	✓	✓
Reverse Polarity Protection		✓	✓	✓	✓	✓
Power Good Signal	✓		✓	✓
Inductive Load Compatibility						✓	✓
Load-Dump Compatibility			✓	✓	✓	✓	✓
Thermal Shutdown	✓	✓	✓	✓		✓

(1) Self protected load switch

Figure 1. Typical Power Switch Use Cases

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1 Load Switches

Figure 2. Load Switch Block Diagram

Integrated load switches are electronic switches that turn power rails on and off. When the internal FET turns on, current flows from the input to output and passes power to the downstream circuitry. When the device is enabled, the rise time of the output voltage (V_OUT) can be controlled by adjusting the capacitance on an external pin (CT pin). When the device is disabled, the fall time of V_OUT is controlled through the quick output discharge (QOD). QOD pulls the output to ground whenever the device is turned off, preventing the output from floating or entering an undetermined state.

Some common functions of load switches include power savings, power sequencing, and inrush current control. Power savings is important in applications looking to minimize current dissipation and maximize power efficiency. By disconnecting the supply from a load or subsystem, the switch minimizes power drawn from inactive loads. Power sequencing is important in applications where individual voltage rails need to be turned on and off in a specific order. By configuring the CT and QOD pins, the ramp-up and power-down timing can be adjusted. Inrush current control protects systems that contain large bulk capacitors near the load. When power is initially applied to the system, charging these capacitors can result in a large inrush current that exceeds the nominal load current. If left unaddressed, this can cause voltage rails to fall out of regulation due to the drop, resulting in the system entering an undesired state. Load switches can mitigate the inrush current by using the CT pin to manage the rise time of the power rail. This leads to a linear output slew rate with no voltage dips or external regulators required.

Table 2. Load Switch Examples⁽¹⁾

DESCRIPTION	DEVICES	VOLTAGE RANGE	MAX CURRENT	TYPICAL R_on	PACKAGE
Adjustable rise time, adjustable QOD	TPS22918	1 V to 5.5 V	2 A	52 mΩ	SOT
Adjustable rise time, adjustable QOD	TPS22810	2.7 V to 18 V	2 A	79 mΩ	SOT
Space-constrained applications	TPS22915	1.05 V to 5.5 V	2 A	37 mΩ	CSP
Space-constrained applications	TPS22916	1 V to 5.5 V	2 A	60 mΩ	CSP
Self protected with controlled rise time	TPS22919	1.6 V to 5.5 V	1.5 A	90 mΩ	SOT
Lowest ON-resistance, power good indication	TPS22990	1 V to 5.5 V	10 A	3.9 mΩ	SON
Fast turn-on time (≤ 65 µs), Power Good indication, QOD, thermal shutdown	TPS22971	0.65 V to 3.6 V	3 A	6.7 mΩ	DSBGA

(1) TI.com/LoadSwitches for more information about load switches.