AAT3142 datasheet(10/16 Pages) AAT

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AAT3142

High Efficiency 1X/1.5X/2X Charge Pump

for White LED Applications

3142.2007.03.1.2

Functional Block Diagram

1.5X

Charge

Pump

Soft-Start

Control

1MHz

Oscillator

Voltage

Reference

32 x 8 bit

ROM

C1+

C1-

C2+

C2-

GND

EN/SET

VIN

S2Cwire

Interface

D/A

Functional Description

The AAT3142 is a tri-mode load switch (1X) and

high efficiency (1.5X or 2X) charge pump device

intended for white LED backlight applications. To

maximize power conversion efficiency, an internal

sensing circuit monitors the voltage required on

each constant current source output and sets the

load switch and charge pump modes based on the

input battery voltage and the current source output

voltage. As the battery discharges over time, the

AAT3142 charge pump is enabled when any of the

three current source outputs nears dropout. The

charge pump initially starts in 1.5X mode. If the

charge pump output drops enough for any current

source output to become close to dropout, the

charge pump will automatically transition to 2X

mode. Each of the three current source outputs is

independently switched between the battery input

(1X) or the charge pump output (1.5X or 2X),

depending on the voltage at the current source out-

put. Since the LED-to-LED forward voltage (V

can vary as much as 1V, this function significantly

enhances overall device efficiency when the bat-

tery input voltage level is greater than the voltage

required at any current source output.

The AAT3142 requires only four external compo-

nents: two 1µF ceramic capacitors for the charge

pump flying capacitors (C

and C

2),

one 1µF

ceramic input capacitor (C

IN), and one 0.33µF to

1µF ceramic charge pump output capacitor (C

CP).

The three constant current outputs (D1 to D3) drive

three individual LEDs with a maximum current of

30mA each. The EN/SET S

2Cwire serial interface

enables the AAT3142 and sets the current source

magnitudes.

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