AAT2805
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
2X
Charge
1MHz
Oscillator
C2+
C2-
Pump
Voltage
Reference
VOUT_BL
D/A
D/A
D/A
D/A
D1
D2
D3
6 X 16 Bit
ROM
Control
Logic
6 X 16 Bit
ROM
EN/SET
D4
GND
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 30mA per LED. 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 and sets the con-
stant current sink magnitudes. AS2Cwire addressing
allows the LED main channels D1-D3 to be con-
trolled independently from the LED sub-channel D4.
The flash charge pump is a charge pump doubler
with regulated output voltage. It is designed to deliv-
er 120mA of continuous current and 250mA of
pulsed current.
Functional Description
The AAT2805 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
inputs near dropout. The charge pump initially starts
in 1.5X mode. If the charge pump output drops
10
2805.2006.04.1.7
AAT [ ADVANCED ANALOG TECHNOLOGY, INC. ]
