High Efficiency 1X/1.5X/2X Charge
Pump for White LED Applications
Functional Block Diagram
C1+
C1- C2+
C2-
AAT3166
IN
1X, 1.5X, 2X
Charge Pump
OUTCP
Soft-Start
Control
1MHz
Oscillator
Voltage
Reference
D/A
6 x 16 Bit
ROM
D/A
D/A
D1
D2
D3
EN/SET
AS
2
Cwire
Interface
6 x 16 Bit
ROM
D/A
D4
GND
Functional Description
The AAT3166 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 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 AAT3166
charge pump is enabled when any of the four cur-
rent 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. The AAT3166
requires only four external components: two 1µF
ceramic capacitors for the charge pump flying
capacitors (C1 and C2), one 1µF ceramic input
capacitor (C
IN
), and one 0.33µF to 1µF ceramic
charge pump output capacitor (C
OUT
).
The four constant current sink inputs (D1 to D4)
can drive four individual LEDs with a maximum cur-
rent of 27mA nominal each. Unused sink inputs
should be connected to OUTCP, otherwise the part
will operate only in 2X charge pump mode. The
AS
2
Cwire serial interface enables the AAT3166
and sets the current sink magnitudes. AS
2
Cwire
addressing allows independent control of two
groups of current sink input: D1~D3 and D4.
Constant Current Output Level Settings
The constant current sink levels for D1 to D4 are
set via the serial interface according to a logarith-
mic scale where each code is approximately 1.8dB
lower than the previous code. In this manner, LED
8
3166.2006.05.1.2
ANALOGICTECH [ ADVANCED ANALOGIC TECHNOLOGIES ]
