AAT3129
High Efficiency 1X/1.5X/2X Charge Pump
for RGB Color LED Applications
Functional Block Diagram
VIN
Soft Start
1X
1.5X
2X
Charge
Pump
C1+
C1-
C2+
C2-
CP
1MHz
Oscillator
Voltage
Reference
ISRC
DR
EN/SET
AS
2
Cwire
Interface
DG
Control
DB
GND
Functional Description
The AAT3129 is a tri-mode load switch (1X) and
high efficiency (1.5X or 2X) charge pump device
intended for fashion color LED lighting applications.
To maximize power conversion efficiency, an inter-
nal sensing circuit monitors the voltage required on
the 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
AAT3129 charge pump is enabled when the current
source output nears dropout. The charge pump ini-
tially starts in 1.5X mode. If the charge pump out-
put drops enough for the current source output to
become close to dropout, the charge pump will
automatically transition to 2X mode.
The AAT3129 requires only four external compo-
nents: 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 output capacitor (C
P
).
The color and brightness of an RGB color LED is
maintained by PWM signals, which are pro-
grammed via the AS
2
Cwire interface. The control
block generates three gate drive PWM signals for
the N-channel MOSFET switches. Please refer to
the interface description and timing in the following
section for details.
3129.2005.11.1.3
9
ANALOGICTECH [ ADVANCED ANALOGIC TECHNOLOGIES ]
