AAT3120 Datasheet, PDF(7/14 Page) Advanced Analogic Technologies – 3-Channel Charge Pump For White LED Applications

English

English German Russian Spanish Italian Polish Chinese Japanese Korean French Portuguese	Language :

AAT3120 Datasheet, PDF (7/14 Pages) Advanced Analogic Technologies – 3-Channel Charge Pump For White LED Applications

◁

Functional Block Diagram

AAT3120

3-Channel Charge Pump

For White LED Applications

VIN

Soft-Start

Control

1MHz

Oscillator

Voltage

Reference

1X / 1.5X

Charge

Pump

C1+

C1-

C2+

C2-

OUT

EN/SET

Single-Wire

Interface

Current

Reference

32 x 16 bit

ROM

Quad

Output

DAC

GND

Functional Description

The AAT3120 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. The 1X load switch / 1.5X charge pump

mode is decided on the voltage sensed on the out-

put D1. Switchover between the 1.5X (charge-

pump) operating mode and the 1X (load switch)

mode occurs automatically (as a function of input

and output voltages) and does not require user

intervention to maintain maximum efficiency.

3120.2005.11.1.1

The AAT3120 requires only four external compo-

nents: two 1ÂµF ceramic capacitors for the charge

pump flying capacitors (C1 and C2), one 1ÂµF

ceramic input capacitor (CIN), and one 0.33ÂµF to

1ÂµF ceramic output capacitor (COUT). 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. The current source output magnitude is con-

trolled by the EN/SET serial data single-wire inter-

face. The interface records rising edges of the

EN/SET pin and decodes them into eight individual

current level settings (see Table 1, Current Level

Settings). Once the final clock cycle is input for the

desired brightness level, the EN/SET pin is held

high to maintain the device output current at the

programmed level. The device is disabled 500Âµs

after the EN/SET pin transitions to a logic low state.

▷