POWER MANAGEMENT

1

© 2008 Semtech Corporation

Typical Application Circuit

Applications

DSLR, DSC, and Video Cameras

Cellular handsets

Portable media players

Personal navigation systems

Satellite radio

Handheld video games

June 20, 2008

High Efficiency Boost Converter

for up to 6 LEDS

SC4539

SC4539

Features

Input voltage range — 2.8V to 5.5V

Programmable LED current up to 30mA

Current-mode PWM control — 800kHz

Soft-start to reduce in-rush current

PWM dimming — 100Hz to 50kHz

PWM dimming at ISET — Analog and filtered

Over-voltage protection — 22V (minimum)

Under-voltage lockout (UVLO)

Thermal shutdown

Shutdown current — <0.1μA (typical)

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

Lead-free package, WEEE and RoHS compliant

Description

The SC4539 is designed to regulate current for a series

string 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 boost

circuit can output up to 22V (guaranteed) to drive up to 6

LEDs in series. 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 shut-

down provide additional protection. A small external

capacitor and series resistor control soft-start and loop

compensation. Over-voltage detection protects the

SC4539 if the BL pin is floating or shorted to ground.

The SC4539 is available in an MLPD-8 pin 2mm x 2mm x

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

to +85°C.

OUT

LX

BL

2.8 to

5.5V

IN

EN

ISET

GND

COMP

Enable and

PWM dimming

L1

D