AP2337

1.0A SINGLE CHANNEL CURRENT-LIMITED LOAD SWITCH

AP2337

Document number: DS35060 Rev. 2 - 2

7 of 10

www.diodes.com

September 2011

© Diodes Incorporated

Application Note

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 AP2337 are outlined below:

NO

Conditions

Explanation

Behavior of the AP2337

1

Short circuit condition at

start-up

Output is shorted before

input voltage is applied or

before the part is powered

up.

The IC senses the short circuit and immediately

clamps output current to a certain safe level

2

Short-circuit or

Overcurrent condition

Short-Circuit or Overload

condition that occurs when

the part is powered up and

above UVLO.

• 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

3

Gradual increase from

nominal operating current

Load increases gradually

until the current-limit

threshold.

has been reached, the device switches into its

Reverse Current Protection

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 feature is implemented in the AP2337 to limit such back currents. This circuit is

activated by the difference between the output voltage and the input voltage (100mV TYP). After the reverse current circuit

600us, output device is disabled and shutdown. This is called the "Deglitch time from reverse current trigger to MOSFET turn

off”. Recovery from IROCP occurs when the output voltage falls to 101% of input voltage.

Over-Voltage Protection

The device has an output over-voltage protection that triggers when the output voltage reaches 114% (TYP) of input

voltage. When this fault condition stays on for longer than 15us (This is called the “Debounce time from output over-voltage to

MOSFET turn off” ) output device is disabled and shutdown. Recovery from ROVP occurs when the output voltage falls to

101% of input voltage.