AAT3113 datasheet(8/15 Pages) AAT

8 / 15 page

AAT3113, AAT3114/14A

High Efficiency 1.5X Fractional Charge

Pumps For White LED Applications

3113.2006.07.1.9

Functional Block Diagram

Voltage

Reference

Soft Start

600kHz

Oscillator

1.5X

Charge

Pump

S2Cwire

Interface

32x8 bit

ROM

Current

Mode

DAC

VIN

C1+

C1-

C2+

C2-

OUT

GND

* AAT3114/14A only

EN/SET

D5*

D6*

Functional Description

The AAT3113 and AAT3114/14A devices are high

efficiency 1.5X fractional charge pumps intended

for white LED backlight applications. The fraction-

al charge pump consists of a linear regulator fol-

lowed by a 1.5X charge pump. The AAT3113 and

AAT3114/14A require only four external compo-

nents: two 1µF ceramic capacitors for the charge

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

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

ceramic capacitor for COUT. The charge pump out-

put is converted into four or six constant current

outputs (D1 to D4 or D6) to drive four or six indi-

vidual LEDs with a maximum of 20mA each. The

current source output magnitude is controlled by

the EN/SET serial data S2Cwire interface. The

interface records rising edges of the EN/SET pin

and decodes them into 32 individual current level

settings each 1dB apart (see Table 1, Current

Level Settings). 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. With each EN/SET pulse, the output

current increases by 1dB. To decrease the output

current by 1dB, 31 EN/SET clock pulses are

required. The counter can be clocked at speeds up

to 1MHz, so intermediate states are not visible.

The first rising edge of EN/SET enables the IC and

initially sets the output LED current to -31dB, the

lowest setting equal to 525µA. Once the final clock

cycle is input for the desired brightness level, the

EN/SET pin is held high to maintain the device out-

put current at the programmed level. The device is

disabled 500µs after the EN/SET pin transitions to

a logic low state.

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