Intelligent Power Switch ICs

Intelligent power switch ICs are employed in applications that include USB ports and peripherals, notebook computers, battery-charger circuits, and hot-swap power supplies. They consist of a power MOSFET and internal circuits that control their turn-on and turn-off. Also, many of these ICs have protection circuits for undervoltage, overtemperature, and overcurrent.

1. One of these ICs employs a 1.0A current-limited P-channel, MOSFET for high-side load-switching applications. This switch operates with inputs ranging from 2.7V to 5.5V. An integrated current-limiting circuit protects the input supply against large changes in load current that may cause the supply to fall out of regulation. It is also protected from thermal overloads, which limit power dissipation and junction temperatures. The current limit threshold is factory programmed at 1.5A, with a maximum of 2.0A. The quiescent supply current is typically 16µA. In its shutdown mode, the supply current decreases to less than 1µA. This IC is a part of a family of adjustable and fixed products with a range of current handling capabilities. Single versions with adjustable current limit or fixed current limit as well as dual versions with fixed current limit.

2. Another IC is a dual high-side power distribution switch that integrates a 110mW N-channel MOSFET. It is intended for applications where heavy capacitive loads and short-circuits are likely to be encountered. A logic enable input, compatible with 3V and 5V logic, is available in active-high or active-low enable. An internal charge pump controls the power switch rise and fall time to minimize current surges during switching, and also provides the gate drive for the internal MOSFET. Requiring no external components, the charge pump allows operation from supplies as low as 3.3V. If an overload or a short circuit is encountered, the IC limits the output current to a safe level by switching into a constant-current mode and sets the overcurrent logic output error flag low. Continuous heavy overloads and short circuits increase the power dissipation in the switch, causing the junction temperature to rise, but a thermal protection circuit shuts the power switch off to prevent damage. Once the device has cooled sufficiently, it turns on automatically. Under voltage lockout (UVLO) insures that the power switch is in the Off state at start-up.

3. A single-channel, high-side power distribution switch has enable, flag functions and adjustable current-limit from 0.7A to 1.25A. It is optimized for self-powered and bus-powered Universal Serial Bus (USB) applications. Soft-start eliminates the momentary voltage drop on the upstream port that may occur when the switch is enabled in bus-powered applications. Additional features include thermal shutdown to prevent catastrophic switch failure from high-current loads, under voltage lockout (UVLO) to ensure that the device remains off unless there is a valid input voltage present, and 3.3V and 5V logic compatible enable inputs.

This IC supports the following USB requirements:

  • Each switch channel supplies up to 700mA as required by USB downstream devices
  • The switch's low on-resistance meets USB voltage drop requirements
  • Fault current limited to typically 900mA to 1.25A
  • Flag output indicates fault conditions to the local USB controller.

4. Another power distribution switch IC serves as the control logic for a system with multiple power sources. The IC directly drives external P-channel MOSFETs to select from an ac adapter and dual battery sources for charge and discharge. It makes the selection based on the presence of the power sources and the state of the batteries. The IC detects low battery conditions using integrated analog comparators and checks for the presence of a battery by using battery thermistor outputs.

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