AAT3151B Datasheet, PDF (8/15 Pages) Advanced Analogic Technologies – High Efficiency 1X/1.5X Charge Pump For White LED Applications

AAT3151B
High Efficiency 1X/1.5X Charge Pump
For White LED Applications
Functional Block Diagram
C1+ C1- C2+ C2-
VIN
EN/SET
Soft-Start
Control
1MHz
Oscillator
Voltage
Reference
AS²Cwire
Interface
1X and 1.5X
Charge Pump
D/A
6 x 16 bit
D/A
ROM
D/A
D/A
VOUT
D1
D2
D3
D4
GND
Functional Description
The AAT3151B is a dual mode load switch (1X)
and high efficiency (1.5X) 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 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 AAT3151B
charge pump is enabled when any of the four cur-
rent sinks near dropout.
The AAT3151B 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 1µF ceram-
ic charge pump output capacitor (C_OUT).
The AAT3151B constant current sinks can drive
four individual LEDs with a maximum current of
30mA per channel. The AS²Cwire serial interface
enables the AAT3151B and sets the constant cur-
rent sink magnitudes.
Constant Current Output Level Settings
The constant current level for the LED channels is
set via the AS²Cwire serial interface according to a
logarithmic scale. In this manner, LED brightness
appears to change linearly when the settings in the
scale are traversed. Because the inputs D1 to D4
are true independent constant current sinks, the
voltage observed on any single given input will be
determined by the difference between V_OUT and the
actual forward voltage (V_F) of the LED being driven.
Since the constant current levels for the AAT3151B
are programmable, no PWM (pulse width modula-
tion) or additional control circuitry are needed to
control LED brightness. This feature greatly reduces
the burden on a microcontroller or system IC to
manage LED or display brightness, allowing the
user to "set it and forget it." With its high-speed seri-
al interface (>1MHz data rate), the LED current
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3151B.2007.09.1.0