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ADM8845
(Rev.:RevD)

Charge Pump Driver for LCD White LED Backlights

Analog Devices 

Data Sheet

FEATURES

Drives 6 LEDs from 2.6 V to 5.5 V (Li-Ion) input supply

1×/1.5×/2× fractional charge pump to maximize power

efficiency

1% maximum 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 mm2 (3 mm × 3 mm)

Package height only 0.75 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 lights

Micro TFT color displays

DSC

PDAs

Charge Pump Driver for LCD

White LED Backlights

ADM8845

GENERAL DESCRIPTION

The ADM8845 uses charge pump technology to provide the

power required to drive up to six LEDs. The LEDs are used for

backlighting a color LCD display, having regulated constant

current for uniform brightness intensity. The main display can

have up to four LEDs, and the sub display can have one or two

LEDs. The digital CTRL1 and CTRL2 input control pins control

the shutdown operation and the brightness of the main and sub

displays.

To maximize power efficiency, the charge pump can operate in

a 1×, 1.5×, or 2× mode. The charge pump automatically

switches between 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 to sense individual LED current with a maximum

matching accuracy of 1%.

FUNCTIONAL BLOCK DIAGRAM

C1

C2

1F

1F

VCC ADM8845

C4

4.7F

CHARGE PUMP

1/1.5/2 MODE

CTRL1

CTRL2

CONTROL

LOGIC

OSC

VREF

ISET

RSET

LED

CURRENT

CONTROL

CIRCUIT

VOUT

C3

2.2F

MAIN

FB1

FB2

FB3

FB4

FB5

FB6

SUB

CURRENT CONTROLLED SINKS

GND

Figure 1.

Rev. D

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