AP2552/AP2553/AP2552A/AP2553A

Document number: DS35404 Rev. 5 - 2

10 of 16

www.diodes.com

December 2012

© Diodes Incorporated

AP2552/ AP2553/ AP2552A/ AP2553A

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Thermal Protection

Thermal protection prevents the IC from damage when the die temperature exceeds safe margins. This mainly occurs when heavy-overload or

short-circuit faults are present for extended periods of time. The AP2552/53 AND AP2552A/53A implements a thermal sensing to monitor the

operating junction temperature of the power distribution switch. Once the die temperature rises to approximately +160°C (140°C in case the part

is under current limit), the thermal protection feature gets activated as follows: The internal thermal sense circuitry turns the power switch off and

the FAULT output is asserted thus preventing the power switch from damage. Hysteresis in the thermal sense circuit allows the device to cool

down by approximately +20°C before the output is turned back on. This built-in thermal hysteresis feature is an excellent feature, as it avoids

undesirable oscillations of the thermal protection circuit. The switch continues to cycle in this manner until the load fault is removed, resulting in

a pulsed output.

Reverse-Current and Reverse-Voltage Protection

The USB specification does not allow an output device to source current back into the USB port. In a normal MOSFET switch, current will flow in

reverse direction (from the output side to the input side) when the output side voltage is higher than the input side. A reverse-current limit

(ROCP)

feature is implemented in the AP2552/53 AND AP2552A/53A to limit such back currents. The ROCP circuit is activated when the output

voltage is higher than the input voltage. After the reverse current circuit has tripped (reached the reverse current trip threshold), the current is

clamped at this IROCP level.

In addition to ROCP, reverse over-voltage protection (ROVP) is also implemented. The ROVP circuit is activated by the reverse voltage

comparator trip point

ie; the difference between the output voltage and the input voltage.

For AP2552/53, once ROVP is activated, FAULT assertion occurs at a de-glitch time of 4ms. Recovery from ROVP is automatic when the fault is

removed. FAULT de-assertion de-glitch time is same as the de-assertion time.