AAT3131 datasheet(7/14 Pages) AAT

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AAT3131

High Efficiency 1X/1.5X Fractional

Charge Pump for White LED Applications

3131.2005.12.1.2

Functional Block Diagram

1X/1.5X

Charge

Pump

Soft-Start

Control

1MHz

Oscillator

Voltage

Reference

Quad

Output

DAC

Single

Output

DAC

Current

Reference

S2Cwire

Interface

32x16 bit

ROM

C1+

C1-

C2+

C2-

OUT

GND

EN/SET

VIN

32x16 bit

ROM

Functional Description

The AAT3131 is a dual mode load switch (1X) and

high efficiency (1.5X) fractional charge pump

device intended for white LED backlight applica-

tions. The fractional charge pump consists of a low

dropout linear voltage regulator followed by a 1.5X

charge pump with multiple current-source outputs.

To maximize power conversion efficiency, an inter-

nal feedback control sensing circuit monitors the

voltage required on the constant current source

outputs.

This control circuit then sets the load

switch and charge pump functions based upon the

input voltage level versus the output voltage level

needed. This function significantly enhances over-

all device efficiency when the input voltage level is

greater than the voltage required at the constant

current source outputs. The 1X load switch/1.5X

charge pump mode decision is based on the volt-

age levels sensed on either the D1 output or the

D4 output, whichever is greater. Switchover

between the 1.5X (charge pump) operating mode

and the 1X (load switch) mode occurs automatical-

ly (as a function of input and output voltages) and

does not require user intervention to maintain max-

imum efficiency.

The AAT3131 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

output

capacitor

OUT).

The

LDO/1.5X charge pump output is converted into

three (D1 to D3) constant current outputs to drive

three individual LEDs with a maximum current of

20mA each, and one (D4) constant current output

with a maximum current of 30mA. The current

source output magnitude is controlled by the

EN/SET serial data interface. The interface records

rising edges of the EN/SET pin and decodes them

into 32 addresses corresponding to individual cur-

rent level settings. The 32 addresses are divided

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