AAT3141_07 Datasheet, PDF (10/16 Pages) Advanced Analogic Technologies – High Efficiency 1X/1.5X/2X Charge Pump for White LED Applications

Functional Block Diagram
AAT3141
High Efficiency 1X/1.5X/2X Charge Pump
for White LED Applications
Soft-Start
Control
1MHz
Oscillator
Voltage
Reference
VIN
1X
1.5X
2X
Charge
Pump
C1+
C1-
C2+
C2-
CP
32 x 8 bit
D/A
D1
ROM
D/A
D2
D/A
D3
EN/SET
AS²Cwire
Interface
32 x 8 bit
D/A
D4
ROM
GND
Functional Description
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.
10
AutoBias Technology
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 (V_F) 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 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 charge pump output capacitor (C_CP).
The four constant current outputs (D1 to D4) drive
four individual LEDs with a maximum current of
30mA each. The EN/SET AS²Cwire serial interface
enables the AAT3141 and sets the current source
magnitudes.
3141.2007.03.1.3