© 2009 Semtech Corporation

POWER MANAGEMENT

1

SC652

Backlight Driver for 5 LEDs with

Charge Pump and PWM Control

Features

Input supply voltage range — 2.9V to 5.5V

Charge pump modes — 1x, 1.5x and 2x

PWM dimming control with low pass filter provides

DC backlight current (not pulsed)

PWM frequency range — 200Hz to 50kHz

Five adjustable current sinks — 500μA to 25mA

Backlight current accuracy ±1.5% typical

Backlight current matching ±0.5% typical

LED float detection

Charge pump frequency — 250kHz

Low shutdown current — 0.1μA typical

Ultra-thin package — 2 x 2 x 0.6(mm)

Fully WEEE and RoHS compliant

Applications

Cellular phones, smart phones, and PDAs

LCD display modules

Portable media players

Digital cameras

Personal navigation devices

Display/keypad backlighting and LED indicators

Description

The SC652 is a high efficiency charge pump LED driver

using Semtech’s proprietary charge pump technology.

Performance is optimized for use in single-cell Li-ion

battery applications.

The device provides backlight current using up to five

matched current sinks. The load and supply conditions

determine whether the charge pump operates in 1x, 1.5x,

or 2x mode.

The maximum current per LED is set by a resistor (R

ISET

)

connected from the ISET pin to the input voltage. The

current can be set between 500μA and 25mA. This current

can be varied by applying a pulse-width modulated (PWM)

signal to the EN/PWM pin. A low-pass filter is used to

develop a DC current level rather than a pulsed current

output, resulting in a more efficient system. The resulting

DC current in each LED (I

BL

) is equal to the maximum

current setting multiplied by the duty cycle of the PWM

control signal. Using this control system, I

BL

can gradually

fade between levels.

With a 2 x 2 (mm) package and 4 small capacitors, the

SC652 provides a complete LED driver solution with a

minimal PCB footprint.

SC652

IN

EN/PWM

GND

OUT

BL1

ISET

2.2μF

C1+

PWM

Signal

2.2μF

BL2

BL3

BL4

C2+

C1-

C2-

BL5

C2

2.2μF

C1

2.2μF

US Patents: 6,504,422; 6,794,926

Typical Application Circuit

March 13, 2009