SC652 Datasheet, PDF (1/16 Pages) Semtech Corporation – Backlight Driver for 5 LEDs with Charge Pump and PWM Control

POWER MANAGEMENT
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
SC652
Backlight Driver for 5 LEDs with
Charge Pump and PWM Control
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 ) is equal to the maximum
BL
current setting multiplied by the duty cycle of the PWM
control signal. Using this control system, I can gradually
BL
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.
Typical Application Circuit
V_BAT = 2.9V to 5.5V
C_IN
2.2μF
PWM
Signal
R_ISET
SC652
IN
OUT
EN/PWM
BL1
BL2
ISET
BL3
BL4
GND
BL5
C1+ C1- C2+ C2-
C1
2.2μF
C2
2.2μF
C_OUT
2.2μF
March 13, 2009
© 2009 Semtech Corporation
US Patents: 6,504,422; 6,794,926
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