AP1538

18V 3A 300KHz BUCK CONVERTER

AP1538 Rev. 5

1 of 13

OCTOBER 2009

DS31451

www.diodes.com

•

Input voltage : 3.6V to 18V

•

•

Output current : up to 3A

•

Duty ratio: 0% to 99% PWM control

•

Oscillation frequency: 300KHz typical

•

Soft-start like, Current limit and Enable function

•

Thermal Shutdown function

•

Built-in internal SW P-channel MOS

•

SOP-8L and SOP-8L-DEP: Available in “Green”

Molding Compound (No Br, Sb)

•

Lead Free Finish / RoHS Compliant (Note 1)

AP1538

consists

of

step-down

switching

regulator

with

PWM control. These devices include a reference voltage source,

oscillation circuit, error amplifier, internal PMOS.

AP1538 provides low-ripple power, high efficiency, and excellent

transient characteristics. The PWM control circuit is able to vary

the duty ratio linearly from 0 up to 99%.

This converter also

contains an error amplifier circuit as well as a soft-start circuit that

prevents overshoot at startup.

An enable function, an over

current protect function and a short circuit protect function are built

inside, and when OCP or SCP happens, the operation frequency

will be reduced from 300KHz to 50KHz. Also, an internal

compensation block is built in to minimum external component

count.

With the addition of an internal P-channel Power MOS, a coil,

capacitors, and a diode connected externally, these ICs can

function as step-down switching regulators. They serve as ideal

power supply units for portable devices when coupled with the

SOP-8L

and

SOP-8L-DEP

mini-packages,

providing

such

outstanding features as low current consumption. Since this

converter can accommodate an input voltage up to 18V, it is also

suitable for the operation via an AC adapter.

•

PC Motherboard

•

LCD Monitor

•

Graphic Card

•

DVD-Video Player

•

Telecom Equipment

•

ADSL Modem

•

Printer and other Peripheral Equipment

•

Microprocessor core supply

Typical Application Circuit

AP 1538

+

-

EN

Cc

R

A

R

B

D1

**

FB

Vcc

Output

CVcc

V

V

IN

R

OCSET

OCSET

C

OUT

C

IN

Option

*

C

OCSET

C

EN

R

EN

Option

100K

L1

22uH

6.8K

1.3K

3K

0.1uF

+

-

C

0.1uF

470uF

***

470uF

0.1uF

Notes:

* Typical feedback compensation (Cc): 5600pF.

** Suggested DIODES Power Schottky P/N: B540 series or PDS540.

R

Features

General Description

Applications