AP2552/AP2553/AP2552A/AP2553A

Document number: DS35404 Rev. 5 - 2

11 of 16

www.diodes.com

December 2012

© Diodes Incorporated

AP2552/ AP2553/ AP2552A/ AP2553A

For AP2552A/53A, once ROVP is activated and when the condition exists for more than 5ms (TYP), output device is disabled and shutdown.

This is called the "Time from Reverse-Voltage Condition to MOSFET Turn Off”. FAULT assertion occurs at a de-glitch time of 4ms after ROVP is

reached. Recovery from this fault is achieved by recycling power or toggling EN. FAULT de-assertion de-glitch time is same as the de-assertion

time.

Special Functions:

Discharge Function

When enable is de-asserted, or when the input voltage is under UVLO level, the discharge function is active. The output capacitor is discharged

through an internal NMOS that has a discharge resistance of 100

Ω. Hence, the output voltage drops down to zero. The time taken for discharge

is dependent on the RC time constant of the resistance and the output capacitor.

FAULT Response

The FAULT open-drain output goes active low for any of following faults: Current limit threshold, short- circuit current limit, reverse-voltage

condition or thermal shutdown. The time from when a fault condition is encountered to when the FAULT output goes low is 7ms (TYP). The

FAULT output remains low until over-current, short-circuit current limit 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 FAULT due to the 7ms

deglitch timeout. This 7-ms timeout is also applicable for over-current recovery and over-temperature recovery. The AP2552/53 and

AP2552-2/53A are designed to eliminate erroneous over-current reporting without the need for external components, such as an RC delay

network.

For the AP2552/53 and AP2552A/53A when the reverse voltage condition is triggered, FAULT output goes low after 4ms (TYP). This 4ms (TYP)

timeout is also applicable for the recovery from reverse voltage fault.

When the ILIM pin is shorted to IN or GND, current-limit threshold and short-circuit current limit will be clamped at typically 75mA.When the ILIM

pin is shorted to IN or GND the AP2552/53 and AP2552A/53A FAULT pin will not assert during current limiting conditions; The FAULT pin will

assert during short circuit conditions.

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. This limits the input

voltage drop during line transients. Placing a high-value electrolytic capacitor on the input (10

μF minimum) and output pin(120µF) is

recommended when the output load is heavy. This precaution also reduces power-supply transients that may cause ringing on the input.

Additionally, bypassing thedeviceoutput with a 0.1

μF to 4.7μF ceramic capacitor improves the immunity of the device to short-circuit transients.

This capacitor also prevents output from going negative during turn-off due to parasiticinductance.

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:

Generic Hot-Plug Applications

In many applications it may be necessary to remove modules or pc boards while the main unit is still operating. These are considered hot-plug

applications. Such implementations require the control of current surges seen by the main power supply and the card being inserted. The most

effective way to control these surges is to limit and slowly ramp the current and voltage being applied to the card, similar to the way in which a

power supply normally turns on. Due to the controlled rise times and fall times of the AP2552/53 AND AP2552A/53A, these devices can be used

to provide a softer start-up to devices being hot-plugged into a powered system. The UVLO feature of the AP2552/53 AND AP2552A/53A also

ensures that the switch is off after the card has been removed, and that the switch is off during the next insertion.