AAT2806
Dual High Efficiency Charge Pump
for White LED and Flash Applications
Functional Block Diagram
C3+
C3-
Soft-Start
2X Charge
Pump
VOUT_FLSH
EN_FLSH
1MHz
Oscillator
VIN
VREF
Soft-Start
Control
C1+
C1-
1X
1.5X
1MHz
Oscillator
C2+
2X
Charge
Pump
C2-
Voltage
Reference
VOUT_BL
D/A
D1
D2
D3
6 x 16 Bit
ROM
D/A
D/A
Control
Logic
6 x 16 Bit
ROM
EN/SET
D/A
D4
GND
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. The four constant current sink
inputs D1 to D4 can drive four individual LEDs with a
maximum current of 20mA per LED. The unused sink
inputs must be connected to VOUT_BL; otherwise, the
part will operate only in 2X charge pump mode. The
Functional Description
The AAT2806 is a dual charge pump designed for
flash and white LED applications. The backlight
charge pump is a tri-mode load switch (1X) and high
efficiency (1.5X or 2X) charge pump device. To max-
imize power conversion efficiency, an internal sens-
ing circuit monitors the voltage required on each con-
stant current sink input and sets the load switch and
charge pump modes based on the input battery volt-
age and the current sink input voltage. As the battery
voltage discharges over time, the white LED charge
pump is enabled when any of the four current sink
2
S Cwire serial interface enables and sets the con-
2
stant current sink magnitudes. S Cwire addressing
allows the LED main channels D1 to D3 to be con-
trolled independently from the LED sub-channel D4.
10
2806.2007.09.1.9
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