Datasheet
Four White LED Backlight Driver
ADM8843
Rev. C
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FEATURES
Drives 4 LEDs from a 2.6 V to 5.5 V (Li-Ion) input supply
1×/1.5×/2× fractional charge pump to maximize
power efficiency
0.3% typical LED current matching
Up to 88% power efficiency over Li-Ion range
Powers main and sub display LEDs with individual shutdown
Package footprint only 9 mm
2
(3 mm × 3 mm)
Package height only 0.55 mm
Low power shutdown mode
Shutdown function
Soft start limiting in-rush current
APPLICATIONS
Cellular phones with main and sub displays
White LED backlighting
Camera flash/strobes and movie light applications
Micro TFT color displays
DSC
PDAs
GENERAL DESCRIPTION
The ADM8843 uses charge pump technology to provide the
power to drive up to four LEDs. The LEDs are used for back-
lighting a color LCD display that has regulated constant current
for uniform brightness intensity. The main display can use up to
three LEDs, and the sub display uses one LED. The CTRL1 and
CTRL2 digital input control pins control the shutdown opera-
tion and the brightness of the main and sub displays.
To maximize power efficiency, the charge pump can operate in
1×, 1.5×, or 2× mode. The charge pump automatically switches
among 1×/1.5×/2× modes, based on the input voltage, to
maintain sufficient drive for the LED anodes at the highest
power efficiency.
Improved brightness matching of the LEDs is achieved by a
feedback pin that senses individual LED current with a typical
matching accuracy of 0.3%.
FUNCTIONAL BLOCK DIAGRAM
CURRENT
CONTROL 1
CURRENT
CONTROL 2
CURRENT
CONTROL 3
CURRENT
CONTROL 4
CONTROL
LOGIC
V
REF
CHARGE PUMP
1×/1.5×/2× MODE
OSC
LED
CURRENT
CONTROL
CIRCUIT
FB1
CURRENT CONTROLLED SINKS
FB2
FB3
FB4
V
OUT
C4
4.7μF
V
CC
C1
1μF
CTRL1
CTRL2
C2
1μF
R
SET
I
SET
GND
C3
2.2μF
ADM8843
05050-001
MAIN SUB
Figure 1.