High Efficiency 1X/1.5X/2X Charge Pump for
Six-Channel White LED Applications
Functional Block Diagram
C1+
C1- C2+
C2-
AAT3164
IN
Soft-Start
Control
1MHz
Oscillator
Voltage
Reference
1x, 1.5x and 2x
Charge Pump
OUT
D/A
D/A
D/A
D/A
D/A
D/A
Maximum
Current
Adjustment
D1
D2
D3
D4
D5
D6
EN/SET
S
2
Cwire
Interface
6 x 16 bit
ROM
GND
RSET
Functional Description
The AAT3164 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 AAT3164
charge pump is enabled when any of the six cur-
rent sink inputs near dropout. The charge pump
initially starts in 1.5X mode. If the charge pump
output droops enough for any current sink input to
become close to dropout, the charge pump will
automatically transition to 2X mode. The AAT3164
requires only four external components: two 1µF
ceramic capacitors for the charge pump flying
capacitors (C
1
and C
2
), one 1µF ceramic input
capacitor (C
IN
), and one 0.33µF to 1µF ceramic
charge pump output capacitor (C
OUT
).
The S
2
Cwire serial interface enables the AAT3164
and sets the current sink magnitudes. Since all cur-
rent sinks are truly independent constant current
sinks, the voltage observed on any single given
input will be determined by the actual forward volt-
age (V
F
) for the LED being driven. Unused sink
inputs must be connected to OUT, otherwise the
part will operate in 2X charge pump mode only.
Constant Current Output Level Settings
The current sink magnitude is controlled by
AnalogicTech's S
2
Cwire serial digital input. The
maximum current is programmed by an external
resistor at the RSET pin. Since each current sink is
programmable, no PWM (pulse width modulation)
or additional control circuitry is needed to control
LED brightness. This feature greatly reduces the
burden on a microcontroller or system IC to man-
age LED or display brightness, allowing the user to
"set it and forget it." With its high-speed serial inter-
face (1MHz data rate), the input sink current can be
changed quickly and easily. The code settings for
the AAT3164 are listed in Table 1.
3164.2006.07.1.0
8
ANALOGICTECH [ ADVANCED ANALOGIC TECHNOLOGIES ]
