AAT3134ISN-T1(2004) データシートの表示（PDF） - Analog Technology Inc

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AAT3134ISN-T1
(Rev.:2004)

High Efficiency 1X/1.5X Fractional Charge Pump for White LED Applications

Analog Technology Inc 

AAT3134

High Efficiency 1X/1.5X Fractional

Charge Pump for White LED Applications

Functional Block Diagram

VIN

Soft Start

Control

1MHz

Oscillator

Voltage

Reference

1x/1.5x

Charge

Pump

C1+

C1-

C2+

C2-

OUT

EN/SET

S2CWire

Interface

Current

Reference

32x16 bit

ROM

32x16 bit

ROM

GND

D1

Quad

D2

Output

DAC

D3

D4

Dual

D5

Output

DAC

D6

Functional Description

The AAT3134 is a dual mode Load Switch (1X) and

high efficiency (1.5X) fractional charge pump device

intended for white LED back light applications. The

fractional charge pump consists of a low dropout lin-

ear voltage regulator followed by a 1.5X charge

pump with multiple current-source outputs. To maxi-

mize power conversion efficiency an internal feed-

back 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 effi-

ciency when the input voltage level is greater then

the voltage required at the constant current source

outputs. The 1X Load Switch/1.5X charge pump

mode decision is based on the voltage levels sensed

on either the D1 output or the D5 output, which ever

is greater. Switchover between the 1.5X (charge-

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

6

mode occurs automatically (as a function of input

and output voltages) and does not require user inter-

vention to maintain maximum efficiency.

The AAT3134 requires only four external compo-

nents: two 1µF ceramic capacitors for the charge

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

ic input capacitor (CIN) and one 0.33µF to 1µF ceram-

ic output capacitor (COUT). The LDO/1.5X charge

pump output is converted into four (D1 to D4) con-

stant current outputs to drive four individual LED's

with a maximum current of 20mA each, and two (D5

and D6) constant current outputs with a maximum

current of 20mA. The current source output magni-

tude 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 current level settings. The 32 addresses

are divided up such that outputs D1-D4 can be con-

trolled independently of outputs D5-D6. For address-

es 1 to 6, 7 to 12, 13 to 18, 19 to 24, and 25 to 30,

outputs D1-D4 start at 0mA and increase from 1mA

to 20mA in four steps. Outputs D5 and D6 remain

3134.2004.04.1.0

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