AAT2803 datasheet(11/16 Pages) AAT

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AAT2803

Six-Channel White LED Backlight

Charge Pump with Flash

2803.2006.12.1.6

Functional Block Diagram

1.5X

Charge

Pump

Soft-Start

Control

1MHz

Oscillator

Voltage

Reference

C2 +

C2 -

C3 +

C3 -

OUT_BL

EN/SET

OUT_FL

REF

Soft-Start

1MHz

Oscillator

Charge Pump

C1+

C1-

EN_FL

D/A

6 x 16 bit

ROM

6 x 16 bit

ROM

AS 2Cwire

Interface

GND

Functional Description

The AAT2803 is a dual charge pump targeted for

backlight and flash applications. The charge pump

for white LED applications is a tri-mode load switch

(1X) and high efficiency (1.5X or 2X) charge pump

device. To maximize power conversion efficiency,

an internal sensing circuit monitors the voltage

required on each constant current sink input and

sets the load switch and charge pump modes based

on the input battery voltage and the current sink

input voltage. As the battery discharges over time,

the backlight charge pump is enabled when any of

the six current sink inputs near dropout. The charge

pump initially starts in 1.5X mode. If the charge

pump output drops enough for any current source

output to become close to dropout, the charge pump

will automatically transition to 2X mode.

For flash applications, charge pump doubler archi-

tecture is used to support the high current demand

required by the application. Charge pump regula-

tion is achieved by sensing the output voltage

through an internal resistor divider network. A

switch doubling circuit is enabled when the divided

output drops below a preset trip point controlled by

an internal comparator. The free-running charge

pump switching frequency is approximately 1MHz.

The charge pump is designed to deliver 120mA of

continuous current and 300mA of pulsed current.

The AAT2803 requires only six external compo-

nents: three 1μF ceramic capacitors for the charge

pump flying capacitors (C1, C2, and C3), one 1μF

ceramic input capacitor (CIN), one 0.33μF to 1μF

ceramic capacitor for the backlight charge pump

output, and one 1μF for the flash charge pump out-

put. The six constant current sink inputs (D1 to D6)

can drive six individual LEDs with a maximum cur-

rent of 30mA each. The unused sink inputs must be

connected to VOUT_BL, otherwise the part will operate

only in 2X charge pump mode. The AS2Cwire serial

interface enables the backlight charge pump and

sets the current sink magnitudes.

AS2Cwire

addressing allows independent control of two

groups of current sink input: D1 to D4 and D5 to D6.

AAT2803 Datasheet(PDF) 11 Page - Advanced Analog Technology, Inc.

AAT2803 Datasheet(HTML) 11 Page - Advanced Analog Technology, Inc.

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