AP2552/AP2553/AP2552A/AP2553A

Document number: DS35404 Rev. 5 - 2

9 of 16

www.diodes.com

December 2012

© Diodes Incorporated

AP2552/ AP2553/ AP2552A/ AP2553A

Application Note

The AP2552/53 AND AP2552A/53A are integrated high-side power switches optimized for Universal Serial Bus (USB) that requires protection

functions. The power switches are equipped with a driver that controls the gate voltage and incorporates slew-rate limitation. This, along with the

various protection features and special functions, makes these power switches ideal for hot-swap or hot-plug applications.

Protection Features:

Under-Voltage Lockout (UVLO)

Whenever the input voltage falls below UVLO threshold (~2.5V), the power switch is turned off. This facilitates the design of hot-insertion

systems where it is not possible to turn off the power switch before input power is removed.

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.

The different overload conditions and the corresponding response of the AP2552/53 AND AP2552A/53A are outlined below:

S.NO

Conditions

Explanation

Behavior of the AP2552/53 AND AP2552A/53A

1

Short-circuit condition at

start-up

Output is shorted before input

voltage is applied or before the

part is enabled

The IC senses the short circuit and immediately clamps output

2

Short-circuit or overcurrent

condition

Short-Circuit or Overload

condition that occurs when the

part 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 switches into current

3

Gradual increase from

nominal operating current to

Load increases gradually until

has been reached, the device switches into its current limiting

Note that when the output has been shorted to GND at extremely low temperature (< -30°C), a minimum 120-

μF electrolytic capacitor on the

output pin is recommended. A correct capacitor type with capacitor voltage rating and temperature characteristics must be properly chosen so

that capacitance value does not drop too low at the extremely low temperature operation. A recommended capacitor should have temperature

characteristics of less than 10% variation of capacitance change when operated at extremely low temp. Our recommended aluminum electrolytic

capacitor type is Panasonic FC series.

Current-Limit Threshold Programming

The current-limit threshold can be programmed using an external resistor. The current-limit threshold is proportional to the current sourced out of

temperature and process. This graph does not include the external resistor tolerance. The traces routing the RLIM resistor to the AP2552/53 and

AP2552A/53A should be as short as possible to reduce parasitic effects on the current-limit accuracy.

limiting upstream power supplies causing the input voltage bus to droop. The resulting minimum current-limit threshold is the intersection of the