AAT3159 Datasheet, PDF (8/15 Pages) Advanced Analogic Technologies – High Efficiency 1X/1.5X/2X Charge Pump for White LED Applications

ChargePump^TM
PRODUCT DATASHEET
AAT3159
High Efficiency 1X/1.5X/2X Charge Pump for White LED Applications
Functional Block Diagram
C1+ C1- C2+ C2-
IN
1x, 1.5x and 2x
Charge Pump
OUT
Soft Start
Control
1MHz
Oscillator
Voltage
Reference
D/A
D1
EN/SET
S2Cwire
Interface
D/A
D2
6x16 bit
ROM
D/A
D3
D/A
D4
Max Current
Adjustment
GND (2)
SET
Functional Description
The AAT3159 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 moni-
tors the voltage required on each constant current sink
input and sets the load switch and charge pump modes
based on the input battery voltage and the current sink
input voltage. As the battery discharges over time, the
AAT3159 charge pump is enabled when any of the four
current sink inputs nears dropout. The charge pump
initially starts in 1.5X mode. If the charge pump output
droops enough for any current source output to become
close to dropout, the charge pump will automatically
transition to 2X mode. The AAT3159 requires only four
external components: 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_OUT).
The four constant current sink inputs (D1 to D4) can
drive four individual LEDs with a maximum current of
40mA each. The unused sink inputs must be connected
to V_OUT; otherwise, the part will operate only in 2X
charge pump mode. The S²Cwire serial interface enables
the AAT3159 and sets the LED current magnitudes.
Constant Current Output Level Settings
The LED current magnitude is controlled by AnalogicTech’s
S²Cwire serial digital interface. The maximum current is
programmed by an external resistor at the SET pin.
Since the current sinks are programmable, no PWM
(pulse width modulation) or additional control circuitry is
needed to control LED brightness. This feature greatly
8
www.analogictech.com
3159.2007.10.1.0