AAT2801
Multi-Mode Charge Pump for
White LED Backlight and Flash Applications
Functional Block Diagram
+
-
C3
C3
2X CP
OUT_FLSH
Soft Start
EN_FLSH
IN
1MHz
Oscillator
VREF
C1+
C1-
C2+
C2-
Soft-Start
Control
1X
1.5X
2X
Charge
Pump
1MHz
Oscillator
Voltage
CP
Reference
D/A
D/A
D/A
D/A
D1
D2
D3
D4
Control
Logic
EN/SET
GND
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.
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
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
2801.2006.04.1.3
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