AAT3169_08 Datasheet, PDF (8/13 Pages) Advanced Analogic Technologies – High Efficiency 1X/1.5X/2X Charge Pump for White LED Applications

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PRODUCT DATASHEET
AAT3169
High Efficiency 1X/1.5X/2X Charge Pump for White LED Applications
Functional Block Diagram
C1+ C1- C2+ C2-
IN
EN/SET
Soft-Start
Control
1MHz
Oscillator
Voltage
Reference
AS²Cwire
Interface
1X, 1.5X, 2X
Charge Pump
OUTCP
Main
6 x 16 Bit
ROM
Sub
6 x 16 Bit
ROM
D/A
D1
D/A
D2
D/A
D3
D/A
D4
D/A
D5
D/A
D6
GND
Functional Description
The AAT3169 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
AAT3169 charge pump is enabled when any of the six
current sink inputs near dropout. The charge pump ini-
tially 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 AAT3169 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 charge pump output capacitor (C_OUT).
The six constant current sink inputs (D1 to D6) can drive
six individual LEDs with a maximum current of 30mA
nominal each. Unused sink inputs should be connected
to OUTCP, otherwise the part will operate only in 2X
charge pump mode. The AS²Cwire serial interface
enables the AAT3169 and sets the current sink magni-
tudes. AS²Cwire addressing allows independent control
of two groups of current sink input: D1~D5 and D6.
Constant Current Output Level Settings
The constant current sink levels for D1 to D6 are set via
the serial interface according to a logarithmic scale
where each code is approximately 1.8dB lower than the
previous code. In this manner, LED brightness appears
linear with each increasing code count. Because the
inputs D1 to D6 are true independent constant current
sinks, the voltage observed on any single given input will
be determined by the actual forward voltage (V_F) for the
LED being driven.
Since the input current sinks of the AAT3169 are pro-
grammable, no PWM (pulse width modulation) or addi-
tional control circuitry is needed to control LED bright-
ness. 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 serial interface (1MHz data rate), the
input sink current of the AAT3169 can be changed suc-
cessively to brighten or dim LEDs in smooth transitions
(e.g., to fade-out) or in abrupt steps, giving the user
complete programmability and real-time control of LED
brightness.
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3169.2008.03.1.3