AAT3122 Datasheet, PDF(7/12 Page) Advanced Analogic Technologies – High Efficiency 1X/1.5X Fractional Charge Pump for White LED Applications

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AAT3122 Datasheet, PDF (7/12 Pages) Advanced Analogic Technologies – High Efficiency 1X/1.5X Fractional Charge Pump for White LED Applications

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AAT3122

High Efficiency 1X/1.5X Fractional Charge

Pump for White LED Applications

Functional Block Diagram

VIN

Soft Start

1MHz

Oscillator

Voltage

Reference

1.5X

Charge

Pump

C1+

C1-

C2+

C2-

OUT

EN/SET

S2Cwire

Interface

5 32x8 bit 8

ROM

Current

Mode

DAC

GND

Functional Description

The AAT3122 is a dual mode load switch (1X) and

high efficiency (1.5X) fractional charge pump device

intended for white LED backlight applications. The

fractional charge pump consists of a low dropout lin-

ear voltage regulator followed by a 1.5X charge

pump. To maximize power conversion efficiency, an

internal feedback control sensing circuit monitors

the voltage required on the constant current source

output. 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 overall device

efficiency when the input voltage level is greater

than the voltage required at the constant current

source output. 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.

The AAT3122 requires only four external compo-

nents: two 1ÂµF ceramic capacitors for the charge

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

ceramic capacitor for CIN, and one 0.33ÂµF to 1ÂµF

ceramic capacitor for COUT. The LDO/1.5X charge

pump output is converted into a constant current

output capable of driving up to six individual LEDs

with a maximum of 20mA each. The current source

output magnitude is controlled by the EN/SET seri-

al data S2Cwire interface. The interface records ris-

ing edges of the EN/SET pin and decodes them into

32 individual current level settings each 1dB apart.

This is summarized in Figure 1 and Table 1. Code

32 is full scale, and Code 1 is full scale attenuated

by 31dB. The modulo 32 interface wraps states

back to State 1 after the 32nd clock.

3122.2005.11.1.3

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