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AP2552/AP2553/AP2552A/AP2553A

Document number: DS35404 Rev. 8 - 2

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www.diodes.com

February 2014

P2552/ 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, AP2552/53 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.

For AP2552A/53A, when an overcurrent condition is detected, the devices will limit the current until the overload condition is removed or the

internal deglitch time (7-ms typical) is reached and AP2552A/53A will be turned off. AP2552A/53A will remain latched off even overload condition

is removed until power is cycled or the device enable is toggled.

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

NO Conditions Explanation Behavior of the AP2552/53

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

current to a certain safe level namely I

SHORT.

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

limiting mode and the current is clamped at I

SHORT

LIMIT

Gradual increase from

nominal operating current to

LIMIT

Load increases gradually until

the current-limit threshold.(I

TRIG

)

The current rises until I

LIMIT

or thermal limit. Once the threshold

has been reached, the device switches into its current limiting

mode and is set at I

LIMIT

NO Conditions Explanation Behavior of the AP2552A/53A

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

current to a certain safe level namely I

SHORT.

When the internal

deglitch time (7-ms typical) is reached and the devices will be

turned off.

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

limiting mode and the current is clamped at I

SHORT

LIMIT

When

the internal deglitch time (7-ms typical) is reached and

the devices will be turned off.

Gradual increase from

nominal operating current to

LIMIT

Load increases gradually until

the current-limit threshold.(I

TRIG

)

The current rises until I

LIMIT

or thermal limit. Once the threshold

has been reached, the device switches into its current limiting

mode and is set at I

LIMIT

. When the internal deglitch time (7-ms

typical) is reached and the devices will be turned off.

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