AP2142A/AP2152A

0.5A DUAL CHANNEL CURRENT-LIMITED POWER

SWITCH WITH OUTPUT DISCHARGE

AP2142A/2152A

Document number: DS32191 Rev. 2 - 2

11 of 17

www.diodes.com

October 2010

© Diodes Incorporated

Application Note

Power Supply Considerations

A 0.1

μF to 1μF X7R or X5R ceramic bypass capacitor between IN and GND, close to the device, 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 1

μF 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

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

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

overload occurs, higher inrush current may flow for a very short period of time before the current limit function can

react. The input capacitor(s) rapidly discharge through the device, activating current limit circuitry. Protection is

achieved by momentarily opening the P-MOS high-side power switch and then gradually turning it on. After the

current limit function has tripped (reached the over-current trip threshold), the device switches into current limiting

In the third condition, the load has been gradually increased beyond the recommended operating current. The

exceeded. The AP2142A/AP2152A 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

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. 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 7-ms deglitch timeout. The

AP2142A/AP2152A 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.

2

Finally, calculate the junction temperature:

Where:

°C