AAT3142
High Efficiency 1X/1.5X/2X Charge Pump
for White LED Applications
Functional Block Diagram
VIN
Soft-Start
Control
C1+
C1-
C2+
C2-
1X
1.5X
1MHz
Oscillator
2X
Charge
Pump
Voltage
Reference
CP
D/A
D/A
D/A
D1
D2
D3
S2Cwire
EN/SET
32 x 8 bit
ROM
Interface
GND
independently switched between the battery input
(1X) or the charge pump output (1.5X or 2X),
depending on the voltage at the current source out-
put. Since the LED-to-LED forward voltage (VF)
can vary as much as 1V, this function significantly
enhances overall device efficiency when the bat-
tery input voltage level is greater than the voltage
required at any current source output.
Functional Description
The AAT3142 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
AAT3142 charge pump is enabled when any of the
three 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. Each of the three current source outputs is
The AAT3142 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 three constant current outputs (D1 to D3) drive
three individual LEDs with a maximum current of
2
30mA each. The EN/SET S Cwire serial interface
enables the AAT3142 and sets the current source
magnitudes.
10
3142.2007.03.1.2
ANALOGICTECH [ ADVANCED ANALOGIC TECHNOLOGIES ]
