POWER MANAGEMENT

1

High Efficiency Boost Converter

for up to 10 LEDs

Typical Application Circuit

July 11, 2007

OUT

LX

BL

2.8 to

5.5V

IN

EN

ISET

GND

COMP

Enable and

PWM dimming

L1

D

SC4538

Applications

White LED Display Backlight Driver

Smartphones and PDAs

Cellular Handsets

MP3 and Portable Media Players

DSC, GPS, Satellite Radio, Game Players

SC4538

Features

Input voltage range — 2.8V to 5.5V

Current-mode PWM control — 800kHz

Programmable LED current up to 30mA

Soft-start to reduce in-rush current

PWM dimming — 100Hz to 50kHz

Analog and filtered-PWM dimming at ISET

Over-voltage protection — 38V (min.)

Under-voltage lockout (UVLO)

Thermal shutdown

Shutdown current — <1μA

Ultra-thin package — 2mm x 2mm x 0.6mm

Lead-free package, WEEE and RoHS compliant

Description

The SC4538 is designed to regulate current for a series

chain of white LEDs in LCD backlighting applications

where small size and high efficiency are priorities. This

device integrates an 800kHz current-mode PWM boost

converter and a 30mA programmable low dropout current

sink regulator.

An external resistor sets the LED current up to 30mA.

PWM dimming (100Hz to 50kHz) may be applied directly

to the enable (EN) pin, or dimming can be controlled by

applying an analog signal to the ISET circuit. The SC4538

drives a string of up to 10 white LEDs with a forward

voltage of 3.8V or less. The current regulator protects

against shorts between the BL and OUT pins and also

eliminates backlight glow during shutdown when using

LEDs with high leakage. Under-voltage lockout and

thermal shutdown provide additional protection. A small

external capacitor and series resistor control soft-start and

loop compensation. Over-voltage detection protects the

SC4538 if the LED pin is floating or shorted to ground.

The SC4538 is available in an MLPD-8 pin 2mmx 2xmm

0.6mm package, with a rated temperature range of -40°C

to +85°C.