AP2281

Single Slew Rate Programmable Load Switch

AP2281 Rev. 4

9 of 13

FEBRUARY 2009

www.diodes.com

Input Capacitor

A 1

μF capacitor is recommended to connect between IN

and GND pins to decouple input power supply glitch and

noise. The input capacitor has no specific type or

ESR (Equivalent

Series

Resistance)

requirement.

However,

for

higher

current

application,

ceramic

capacitors are recommended due to their capability to

withstand input current surges from low impedance

sources, such as batteries in portable applications. This

input capacitor must be located as close as possible to

the device to assure input stability and less noise. For

PCB layout, a wide copper trace is required for both

IN and GND.

Output Capacitor

A 0.1

μF capacitor is recommended to connect between

OUT and GND pins to stabilize and accommodate load

transient condition. The output capacitor has no specific

type

or

ESR

requirement.

The

amount

of

the

capacitance may be increased without limit. For

PCB layout, the output capacitor must be placed as

close as possible to OUT and GND pins, and keep the

traces as short as possible.

ENABLE/SHUTDOWN Operation

The AP2281 is turned on by setting the EN pin high, and

is turned off by pulling it low. To ensure proper operation,

the signal source used to drive the EN pin must be able

to swing above and below the specified turn-on/off

voltage thresholds listed in the Electrical Characteristics

DISCHARGE Operation

The AP2281-3 offers discharge option that helps to

discharge the output charge when disabled.

Power Dissipation

The device power dissipation and proper sizing of the

thermal plane is critical to avoid thermal shutdown and

ensure reliable operation. Power dissipation of the

device depends on input voltage and load conditions and

can be calculated by:

DSON

2

OUT

D

xR

I

P

=

(1)

However, the maximum power dissipation that can be

handled by the device depends on the maximum

junction to ambient thermal resistance, maximum

ambient temperature, and maximum device junction

temperature, which can be approximated by the

equation below:

JA

A

A

D

)

T

C

125

(

)

T

(max@

P

θ

−

°

+

=

(2)

temperature rise from ambient is approximately 49°C.

Since the maximum junction temperature is 125°C, the

operating ambient temperature must be kept below 76°C

to safely operate the device.

calculated maximum power dissipation from equation (2)

operating maximum continuous current is 1.81A. For

other

application

conditions,

the

users

should

recalculate the device maximum power dissipation

based on the operating conditions.

Application Note