AAT3141
High Efficiency 1X/1.5X/2X Charge Pump
for White LED Applications
Functional Block Diagram
VIN
Soft-Start
Control
C1+
C1-
1X
1.5X
2X
Charge
Pump
1MHz
Oscillator
C2+
C2-
Voltage
Reference
CP
32 x 8 bit
ROM
D/A
D/A
D/A
D/A
D1
D2
D3
D4
AS2Cwire
EN/SET
32 x 8 bit
ROM
Interface
GND
AutoBias Technology
Functional Description
Each of the four current source outputs is inde-
pendently switched between the battery input (1X)
or the charge pump output (1.5X or 2X), depending
on the voltage at the current source output. Since
the LED-to-LED forward voltage (VF) can vary as
much as 1V, this function significantly enhances
overall device efficiency when the battery input
voltage level is greater than the voltage required at
any current source output.
The AAT3141 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 source output and sets the
load switch and charge pump modes based on the
input battery voltage and the current source output
voltage. As the battery discharges over time, the
AAT3141 charge pump is enabled when any of the
four current source outputs nears 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 AAT3141 requires only four external compo-
nents: two 1µF ceramic capacitors for the charge
pump flying capacitors (C1 and C2), one 1µF
ceramic input capacitor (CIN), and one 0.33µF to
1µF ceramic charge pump output capacitor (CCP).
The four constant current outputs (D1 to D4) drive
four individual LEDs with a maximum current of
2
30mA each. The EN/SET AS Cwire serial interface
enables the AAT3141 and sets the current source
magnitudes.
10
3141.2007.03.1.3
ANALOGICTECH [ ADVANCED ANALOGIC TECHNOLOGIES ]
