AP22802

Document number: DS36218 Rev. 3 - 2

11 of 14

www.diodes.com

August 2015

© Diodes Incorporated

AP22802

965010

Application Information

Power Supply Considerations

A 1μF X7R or X5R ceramic bypass capacitor between IN and GND, close to the device, is recommended. Placing a high-value capacitor (10μF

minimum) on both input and output pins is recommended when the output transient load is heavy. This precaution reduces power-supply

transients that may cause ringing on the input. Additionally, bypassing the output with a

0.01μF to 0.1μF ceramic capacitor improves the immunity

of the device to short-circuit transients.

FLG Response

When an over-current or over-temperature shutdown condition is encountered, the FLG open-drain output goes active low after a nominal 6ms

deglitch timeout. The FLG output remains low until both over-current and over-temperature conditions are removed. Connecting a heavy

capacitive load to the output of the device can cause a momentary over-current condition, which does not trigger the FLG due to the 6ms deglitch

timeout. The AP22802 is designed to eliminate false over-current reporting without the need of external components to remove unwanted pulses.

Over-Current and Short Circuit Protection

An internal sensing FET is employed to check for over-current conditions. Unlike current-sense resistors, sense FETs do not increase the series

resistance of the current path. When an overcurrent condition is detected, the device maintains a constant output current and reduces the output

voltage accordingly. Complete shutdown occurs only if the fault stays long enough to activate thermal limiting.

Three possible overload conditions can occur. In the first condition, the output has been shorted to GND before the device is enabled or before

VIN has been applied. The AP22802 senses the short circuit and immediately clamps output current to a certain safe level.

In the second condition, an output short or an overload occurs while the device is enabled. At the instance the overload occurs, higher current

may flow for a very short period of time before the current limit function can react. After the current limit function has tripped, the device switches

In the third condition, the load has been gradually increased beyond the recommended operating current. The current is permitted to rise until the

current-limit threshold without damaging the device. Once the threshold has been reached, the device switches into its current limiting mode and

Thermal Protection

Thermal protection prevents the IC from damage when heavy-overload or short-circuit faults are present for extended periods of time. The

AP22802 implements a thermal sensing to monitor the operating junction temperature of the power distribution switch. Once the die temperature

rises to approximately +140°C due to excessive power dissipation in an over-current or short-circuit condition 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 allowing the device to

cool down approximately +60°C before the switch turns back on. The switch continues to cycle in this manner until the load fault or input power is

removed. The FLG open-drain output is asserted when an over-temperature shutdown or over-current occurs with 6ms deglitch.

ON/OFF Input Operator

The EN input allows the output current to be switched on and off using a GPIO compatible input. The high signal (switch on) should be at least

1.5V, and the low signal (switch off) no higher than 0.5V. This pin should NOT be left floating. It is advisable to hold the EN signal low when

applying or removing power.

Under-voltage lockout function (UVLO) keeps the internal power switch from being turned on until the power supply has reached at least 2V, even

if the switch is enabled. Whenever the input voltage falls below approximately 2V, the power switch is quickly turned off. This facilitates the design

of hot-insertion systems where it is not possible to turn off the power switch before input power is removed.

Discharge Function

The discharge function of the device is active when enable is disabled or de-asserted. The discharge function with the N-MOS power switch

implementation is activated and offers a resistive discharge path for the external storage capacitor. This is designed for discharging any residue of

the output voltage when either no external output resistance or load resistance is present at the output.