AAT3113 datasheet(7/14 Pages) ANALOGICTECH

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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 only

EN/SET

D5*

D6*

AAT3113/4

High Efficiency 1.5X Fractional Charge

Pumps For White LED Applications

3113.2004.07.1.4

Functional Description

The AAT3113/4 is a high efficiency 1.5X fractional

charge pump device intended for white LED back

light applications. The fractional charge pump con-

sists of a linear regulator followed by a 1.5X charge

pump. The AAT3113/4 requires only four external

components: 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

output is converted into four or six constant current

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

ual LEDs with a maximum of 20mA each. The cur-

rent source output magnitude is controlled by the

EN/SET serial data S2C interface. The interface

records rising edges of the EN/SET pin, and

decodes them into 32 individual current level set-

tings each 1dB apart (see Current Level Settings

below). 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 increas-

es 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 intermedi-

ate 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 output current at the pro-

grammed level. The device is disabled 500µs after

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

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