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Operation

HM9715A is an integrated power switch with a low Rdson P-channel MOSFET, internal gate rive circuit,

programmable current limiting, and thermal protection. When the device is active, if there is no load, the device only

consumes 25uA supply current, which makes the device suitable for battery powered applications.

Power Supply Considerations

A 0.01-μF to 0.1-μF ceramic bypass capacitor between IN and GND, close to the device, is recommended.

Placing a high-value electrolytic capacitor on the output pin(s) is recommended when the output load is heavy. This

precaution reduces power-supply transients that may cause ringing on the input and minimize the input voltage droops.

Additionally, bypassing the output with a 0.01-μF to 0.1-μF ceramic capacitor improves the immunity of the device to

short-circuit transients.

Power Dissipation and Junction Temperature

The low on-resistance on the P-channel MOSFET allows the small surface-mount packages to pass large currents. It

is good design practice to check power dissipation and junction temperature for each application. Begin by determining

2

Finally, calculate the junction temperature:

Where:

Compare the calculated junction temperature with the maximum junction temperature which is 125

C. If they are within

degrees, either the maximum load current needs to be reduced or another package option will be required.

FLT Output

The FAULT Flag (FLT) is provided to alert the system if a

HM9715A load is not receiving sufficient voltage to operate

properly. If current limiting circuit is active for more than approximately 4ms, the FAULT Flag is pulled to ground

through an approximately 100Ω resistor. The filtering of voltage or current transients of less than 4ms prevents

capacitive loads connected to the

HM9715A output from activating the FAULT Flag when they are initially attached.

However, if the device is entering over-temperature conditions, the FLT will be pulled low without delay or deglitch.

Pull-up resistance of 1kΩ to 100kΩ on FLT pin is recommended. Since FLT is an open drain terminal, it may be pulled

up to any unrelated voltage less than the maximum operating voltage of 5.5V, allowing for level shifting between

circuits.

Thermal Protection

Thermal protection prevents damage to the IC when heavy-overload or short-circuit faults are present for extended

periods of time. The

HM9715A implements a thermal sensing to monitor the operating junction temperature of the

power distribution switch. In an overcurrent or short-circuit condition, the junction temperature rises due to excessive

power dissipation. Once the die temperature rises to approximately 135°C due to overcurrent conditions, the internal

thermal sense circuitry turns the power switch off, thus preventing the power switch from damage. Hysteresis is built

into the thermal sense circuit, and after the device has cooled approximately 15°C, the switch turns back on. The

switch continues to cycle in this manner until the load fault or input power is removed.

PCB Layout Guide

PCB layout is very important to achieve stable operation. It is highly recommended to duplicate EVB layout for

optimum performance. If change is necessary, please follow these guidelines for reference.

1) Keep the path of current short and minimize the loop area formed by Input and output capacitor.

2) Output capacitor and IC must be on the same side, The distance of outpin and output capacitor <3mm is

recommended.

90mΩ，

A Current Limited USB Power Switch

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