AAT2801 Datasheet, PDF (13/20 Pages) Advanced Analogic Technologies – Multi-Mode Charge Pump for White LED Backlight and Flash Applications

AAT2801
Multi-Mode Charge Pump for
White LED Backlight and Flash Applications
Functional Block Diagram
EN_FLSH
IN
EN/SET
Soft Start
1MHz
Oscillator
Soft-Start
Control
1MHz
Oscillator
Voltage
Reference
Control
Logic
GND
C3⁺ C3 ^-
2X CP
1X
1.5X
2X
Charge
Pump
D/A
D/A
D/A
D/A
V_REF
OUT_FLSH
C1+
C1-
C2+
C2-
CP
D1
D2
D3
D4
Functional Description
The AAT2801 is a dual charge pump for white
LED and flash applications. The charge pump for
white LED application is a tri-mode load switch
(1X) and high efficiency (1.5X or 2X) charge
pump device intended for white LED backlight
applications. To maximize power conversion effi-
ciency, an internal sensing circuit monitors the
voltage required on each constant current source
output and sets the load switch and charge pump
modes based on the input battery voltage and the
current source output voltage. As the battery dis-
charges over time, the AAT2801 charge pump is
enabled when any of the four current source out-
puts nears dropout. The charge pump initially
2801.2006.04.1.3
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.
The second section of the AAT2801 contains a
voltage doubling charge pump to supply flash LED
functions. The voltage doubling charge pump pro-
vides a 4.5V regulated output and has an inde-
pendent enable control.
AutoBias Technology
Each of the four current source outputs for the
white LED backlight charge pump section is inde-
pendently switched between the battery input (1X)
or the charge pump output (1.5X or 2X), depending
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