High Efficiency 1X/1.5X/2X Charge
Pump for White LED Applications
Functional Block Diagram
C1+
C1- C2+
C2-
AAT3167
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
D/A
6 x 16 Bit
ROM
D/A
D1
D2
D3
D4
D5
EN/SET
AS
2
Cwire
Interface
GND
Functional Description
The AAT3167 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 AAT3167
charge pump is enabled when any of the five cur-
rent sink inputs near dropout. The charge pump ini-
tially starts in 1.5X mode. If the charge pump out-
put droops enough for any current source output to
become close to dropout, the charge pump will
automatically transition to 2X mode. The AAT3167
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 five constant current sink inputs (D1 to D5) can
drive five individual LEDs with a maximum current
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 AAT3167 and
sets the current sink magnitudes. AS
2
Cwire
addressing allows independent control of two
groups of current sink input: D1~D4 and D5.
Constant Current Output Level Settings
The constant current sink levels for D1 to D5 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 D5 are true
8
3167.2007.03.1.4
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