SC656 Datasheet, PDF (1/17 Pages) Semtech Corporation – Backlight Driver for 7 LEDs with Charge Pump and PWM Control

SC656
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)
 Two independently configurable backlight banks
 PWM frequency range — 200Hz to 50kHz
 Seven 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 — 3 x 3 x 0.6(mm)
 Fully WEEE and RoHS compliant, and halogen free.
Applications
 Cellular phones, smart phones, and PDAs
 LCD display modules
 Portable media players
 Digital cameras
 Personal navigation devices
 Display/keypad backlighting and LED indicators
Backlight Driver for 7 LEDs with
Charge Pump and PWM Control
Description
The SC656 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 seven
matched current sinks. The load and supply conditions
determine whether the charge pump operates in 1x, 1.5x,
or 2x mode. The seven backlights can be configured as a
single group or split into two independent banks by
setting the state of the BANK2 and BANK1 pins. If only one
bank is needed, the BANK2, BANK1, ENS and ISETS pins
must be grounded.
The maximum current per LED in each bank is set by a
resistor connected to ISETM or ISETS. LED current can be
set between 500µA and 25mA. Backlight current is varied
by applying a pulse-width modulated (PWM) signal to the
ENM pin for the main LED bank and the ENS pin for the
sub LED bank. The resulting DC current in each LED (I_BL) is
equal to the maximum current setting multiplied by the
duty cycle of the PWM signal. During PWM operation, a
low-pass filter is used to develop a DC current through the
LED. The resulting power conversion is more efficient than
comparable pulsed current solutions. Backlight fading is
initiated when the duty cycle is changed.
Typical Application Circuit
The 3 x 3 (mm) package and minimal number of small
external components make the SC656 an ideal backlight
driver solution for space-limited designs.
VBAT = 2.9V to 5.5V
CIN
2.2µF
SC656
IN
OUT
GND
RISETM
RISETS
ISETM
ISETS
BL1
BL2
BL3
BANK2
BL4
BANK1
BL5
PWM Signal
ENM
BL6
PWM Signal
ENS
BL7
C1+ C1- C2+ C2-
COUT
2.2µF
September 24, 2009
C1
2.2µF
C2
2.2µF
© 2009 Semtech Corporation
US Patents: 6,504,422; 6,794,926