AP1539

18V 4A 300KHz BUCK CONVERTER

AP1539 Rev. 4

1 of 13

OCTOBER 2009

DS31477

www.diodes.com

•

Input voltage: 3.6V to 18V

•

•

Output current: up to 4A

•

Duty ratio: 0% to 99% PWM control

•

Oscillation frequency: 300KHz typ.

•

Soft-start like, Current limit and Enable function

•

Thermal Shutdown function

•

Built-in internal SW P-channel MOS

•

SOP-8L-DEP: Available in “Green” Molding Compound

(No Br, Sb)

•

Lead Free Finish / RoHS Compliant (Note 1)

AP1539 consists of step-down switching regulator with PWM

control. These devices include a reference voltage source,

oscillation circuit, error amplifier, internal PMOS.

AP1539 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-DEP mini-package, 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 1539

+

-

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

R

L1

22uH

6.8K

1.3K

3.9K

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.

Features

General Description

Applications