Charge Pump Driver for LCD
White LED Backlights
Preliminary Technical Data
ADM8845
GENERAL DESCRIPTION
FEATURES
ADM8845 drives 6 LEDs from a 2.6 V to 5.5 V (li-ion) input
supply
1x/1.5x/2x Fractional Charge Pump to maximise power
efficiency
1% Max LED Current Matching
Up to 88% Power Efficiency over Li-ion Range
Powers Main and Sub Display LEDs with individual
shutdown
Package footprint only 9mm2 (3mm x 3mm)
Package height only 0.9mm
Low power shutdown mode
Shutdown Function
The ADM8845 provides the power required to drive up to six
LEDs, using charge pump technology. The LEDs are used for
backlighting a color LCD display, with up to four LEDs in the
main display and up to two LEDs in the sub display, with
regulated constant current for uniform brightness intensity.
Two digital input control pins, CTRL1 and CTRL2 control the
shutdown operation and the brightness of the main and sub
displays.
To maximize power efficiency, a charge pump that can operate
in either of a 1x, 1.5x or 2x mode is used. The charge pump
automatically switches between 1x/1.5x/2x modes based on the
input voltage, to maintain sufficient drive for the LED anodes at
the highest power efficiency.
Soft-start limiting inrush current
APPLICATIONS
Improved brightness matching of the LEDs is achieved by the
use of a feedback pin to sense individual LED current with a
maximum matching accuracy of 1%.
Mobile phones with Main and Sub Displays
White LED Backlighting
Camera Flash/Strobes and Movie Light Applications
Micro TFT color displays
DSC
PDA’s
FUNCTIONAL BLOCK DIAGRAM
C1
C2
VCC
ADM8845
Vout
Charge Pump
C4
C3
1x/1.5x/2x mode
SUB
MAIN
+
-
Osc
CTRL1
CTRL2
Control
Logic
FB1
FB2
FB3
FB4
Vref
FB5
FB6
LED Current
Control
Current
Control
1
Current
Control
2
Current
Control
3
Current
Control
5
Current
Control
4
Current
Control
6
Iset
Circuit
Rset
Current Controlled Sinks
GND
Figure 1. ADM8845 FUNCTIONAL BLOCK DIAGRAM
Rev. PrJ_06/04
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