Diodes AP2552/ AP2553/ AP2552A/ AP2553A - Manual (Page 9)

AP2552/AP2553/AP2552A/AP2553A
Document number: DS35404 Rev. 8 - 2
9 of 16
www.diodes.com
February 2014
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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, 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
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
current to a certain safe level namely I
SHORT.
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
limiting mode and the current is clamped at I
SHORT
/I
LIMIT
.
3
Gradual increase from
nominal operating current to
I
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
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
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.
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
limiting mode and the current is clamped at I
SHORT
/I
LIMIT
.
When the internal deglitch time (7-ms typical) is reached and
the devices will be turned off.
3
Gradual increase from
nominal operating current to
I
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.