AAT2846_08 Datasheet, PDF(9/22 Page) Advanced Analogic Technologies – High Current Charge Pump with Dual LDO for Backlight and Flash Applications

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AAT2846_08 Datasheet, PDF (9/22 Pages) Advanced Analogic Technologies – High Current Charge Pump with Dual LDO for Backlight and Flash Applications

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PRODUCT DATASHEET

AAT2846

ChargePumpTM High Current Charge Pump with Dual LDO for Backlight and Flash Applications

Functional Block Diagram

C1+

C1-

C2+

C2-

ENA

ENB

1x/1.5x/2x

Charge Pump

To LDO A

To LDO B

LDO A

LDO B

1.2V

VREF

ENS

FEN

FSET

Control

Logic

AGND PGND

OUTA

FBA

OUTB

FBB

REF

OUT

BL1

BL2

BL3

BL4

BL5

BL6

FL1

FL2

Functional Description

The AAT2846 is a highly integrated backlight and flash

LED driver with two LDO linear regulators. The charge

pump LED driver drives backlight and flash LEDs from a

2.7V to 5.5V input voltage. The LDO regulators are oper-

ated from the same input voltage range and produce

regulated output voltages as low as 1.2V.

LED Drivers

The LEDs are driven from an internal charge pump that,

depending on the battery voltage and LED forward volt-

age, drives LEDs directly from the supply voltage (1X or

bypass mode) or steps up the supply voltage by a factor

of 1.5 (1.5X mode) or 2 (2X mode). The charge pump

requires only two tiny 1ÂµF ceramic capacitors, providing a

more compact solution than typical inductor-based step-

up converter solutions. Each individual LED is driven by a

current sink to AGND, allowing individual current control

with high accuracy over a wide range of input voltages and

LED forward voltages while maintaining high efficiency.

The charge pump is controlled by the voltage across the

LED current sinks. When any one of the active current

sinks begins to dropout, the charge pump goes to the

next higher mode (from 1X to 1.5X or from 1.5X to 2X

mode) to maintain sufficient LED voltage for constant

LED current. The AAT2846 continuously monitors the

LED forward voltages and uses the input voltage to

determine when to reduce the charge pump mode for

better efficiency. There is also a 500mV mode-transition

hysteresis that prevents the charge pump from oscillat-

ing between charge pump modes.

2846.2008.03.1.1

www.analogictech.com

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