AP2401A/AP2411A

Document number: DS37744 Rev. 1 - 2

10 of 18

www.diodes.com

March 2015

© Diodes Incorporated

AP2401A/AP2411A

Application Information

Power Supply Considerations

A 0.1µF to 2.2µF X7R or X5R ceramic bypass capacitor placed between IN and GND, close to the device, is recommended. When an external

power supply is used, or an additional ferrite bead is added to the input, high inrush current may cause voltage spikes higher than the device

maximum input rating during short circuit condition. In this case a 2.2µF or bigger capacitor is recommended. Placing a high-value electrolytic

capacitor on the input and output pin(s) is recommended when the output load is heavy. This precaution reduces power-supply transients that

may cause ringing on the input. Additionally, bypassing the output with a 0.1µF to 1.0µF ceramic capacitor improves the immunity of the device

to short-circuit transients.

Overcurrent and Short Circuit Protection

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

resistance of the current path. When an overcurrent condition is detected, the devices will limit the current until the overload condition is removed

or the internal deglitch time (7ms typical) is reached and the device is turned off. The device will remain latched off even the overload condition is

removed until power is cycled or the device enable is toggled.

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 AP2401A/AP2411A senses the short circuit and immediately clamps output current to a certain safe level namely

ILIMIT, and turns off after deglitch time (7ms typical).

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 (reached the

overcurrent trip threshold), the device switches into current limiting mode and the current is clamped at ILIMIT current for deglitch time period

(7ms typical), and then turned off.

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 (ITRIG) is reached or until the thermal limit of the device is exceeded. The AP2401A/AP2411A is capable of delivering

current up to the current-limit threshold without damaging the device. Once the threshold has been reached, the device switches into its current

limiting mode and output current is clamped at ILIMIT for deglitch time period (7ms typical), and then turned off.

FLG Response

When an overcurrent or over-temperature shutdown condition is encountered, the FLG open-drain output goes active low after a nominal 7ms

deglitch timeout.

When that happens, the FLG will remain low and the switch will be latched off until the fault condition is removed. Connecting a heavy capacitive

load to the output of the device can cause a momentary overcurrent condition, which does not trigger the FLG due to the 7ms deglitch timeout.

The AP2401A/AP2411A is designed to eliminate false, overcurrent reporting without the need of external components to remove unwanted

pulses.

Power Dissipation and Junction Temperature

The low, on-resistance of the internal MOSFET allows the small surface-mount packages to pass large current. Using the maximum operating

ambient temperature (TA) and RDS(ON), the power dissipation can be calculated by:

PD = RDS(ON)× I

2

Finally, calculate the junction temperature:

TJ = PD x RθJA + TA

Where:

TA= Ambient Temperature°C

RθJA = Thermal Resistance

PD = Total Power Dissipation

Thermal Protection

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

AP2401A/AP2411A 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 overcurrent 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 25°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 occurs with 7ms deglitch.

When the FLG is asserted, the switch will be latched off until the temperature drops to 20°C below the thermal shutdown threshold and the power

or EN pin is cycled.