High Efficiency 1X/1.5X/2X Charge Pump with
PWM Control for White LED Applications
Functional Block Diagram
C1+
C1- C2+
C2-
AAT3143
IN
1X/1.5X/2X
Charge Pump
CP
Soft-Start
Control
1MHz
Oscillator
Voltage
Reference
D/A
D/A
D/A
D/A
D1
D2
D3
D4
EN/PWM
EN/PWM
GND
Functional Description
The AAT3143 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
AAT3143 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 AAT3143 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 four constant current source outputs (D1 to
D4) can drive four individual LEDs with a maximum
current of 20mA each. The unused source outputs
must be connected to GND, otherwise the part will
operate only in 2X charge pump mode. The
EN/PWM input allows the user to control the bright-
ness of the four LEDs by PWMing up to 50kHz.
8
3143.2006.05.1.0
ANALOGICTECH [ ADVANCED ANALOGIC TECHNOLOGIES ]
