AP2162/AP2172

1A DUAL CHANNEL CURRENT-LIMITED POWER

SWITCH

AP2162/AP2172 Rev. 5

13 of 17

FEBRUARY 2009

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Application Note

Power Supply Considerations

A 0.01-

μF to 0.1-μF 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 0.01-

μF to 0.1-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

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 over-current trip threshold), the device

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

the device is exceeded. The AP2162/AP2172 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

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 AP2162/AP2172 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

calculated by:

2

Finally, calculate the junction temperature:

Where:

°C