High Efficiency 1X/1.5X/2X Charge
Pump for White LED Applications
Functional Block Diagram
C1+
C1- C2+
C2-
AAT3169
VIN
1X, 1.5X, 2X
Charge Pump
VOUT
Soft-Start
Control
1MHz
Oscillator
Voltage
Reference
D/A
6 x 16 bit
ROM
D/A
D/A
D/A
D/A
6 x 16 bit
ROM
D/A
D1
D2
D3
D4
D5
D6
EN/SET
AS
2
Cwire
Interface
GND
Functional Description
The AAT3169 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 AAT3169
charge pump is enabled when any of the six current
sink inputs near dropout. The charge pump initially
starts in 1.5X mode. If the charge pump output
droops enough for any current source output to
become close to dropout, the charge pump will
automatically transition to 2X mode. The AAT3169
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
).
8
The six constant current sink inputs (D1 to D6) can
drive six individual LEDs with a maximum current
of 30mA nominal each. Unused sink inputs are
connected to V
OUT
, otherwise the part will operate
only in 2X charge pump mode. The AS
2
Cwire seri-
al interface enables the AAT3169 and sets the cur-
rent sink magnitudes. AS
2
Cwire addressing allows
independent control of two groups of current sink
input: D1~D5 and D6.
Constant Current Output Level Settings
The constant current sink levels for D1 to D6 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
brightness appears linear with each increasing
code count. Because the inputs D1 to D6 are true
independent constant current sinks, the voltage
observed on any single given input will be deter-
mined by the actual forward voltage (V
F
) for the
LED being driven.
3169.2006.04.1.0
ANALOGICTECH [ ADVANCED ANALOGIC TECHNOLOGIES ]
