AP2401/AP2411

Document number: DS35113 Rev. 6 - 2

10 of 18

www.diodes.com

March 2013

© Diodes Incorporated

AP2401/AP2411

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.

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 devices will limit the current until the overload condition is removed

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

and turns off after deglitch time(7-ms 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

(7-ms 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

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

FLG Response

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

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 over-current condition, which does not trigger the FLG due to the 7-ms deglitch timeout.

The AP2401/AP2411 is designed to eliminate false over-current 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

2

Finally, calculate the junction temperature:

Where:

Thermal Protection

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

AP2401/AP2411 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 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 7-ms 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.