AAT2803 Datasheet, PDF (11/16 Pages) Advanced Analogic Technologies – Six-Channel White LED Backlight Charge Pump with Flash

AAT2803
Six-Channel White LED Backlight
Charge Pump with Flash
Functional Block Diagram
EN_FL
Soft-Start
1MHz
Oscillator
C1⁺ C1^-
2X
Charge Pump
V_IN
EN/SET
AS ²Cwire
Interface
Soft-Start
Control
1MHz
Oscillator
Voltage
Reference
1X
1.5X
2X
Charge
Pump
6 x 16 bit
ROM
6 x 16 bit
ROM
V_REF
D/A
D/A
D/A
D/A
D/A
D/A
V_{OUT_FL}
C2 +
C2 -
C3 +
C3 -
V_{OUT_BL}
D1
D2
D3
D4
D5
D6
GND
Functional Description
The AAT2803 is a dual charge pump targeted for
backlight and flash applications. The charge pump
for white LED applications is a tri-mode load switch
(1X) and high efficiency (1.5X or 2X) charge pump
device. 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 backlight charge pump is enabled when any of
the six current sink inputs near 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.
For flash applications, charge pump doubler archi-
tecture is used to support the high current demand
required by the application. Charge pump regula-
tion is achieved by sensing the output voltage
2803.2006.12.1.6
through an internal resistor divider network. A
switch doubling circuit is enabled when the divided
output drops below a preset trip point controlled by
an internal comparator. The free-running charge
pump switching frequency is approximately 1MHz.
The charge pump is designed to deliver 120mA of
continuous current and 300mA of pulsed current.
The AAT2803 requires only six external compo-
nents: three 1μF ceramic capacitors for the charge
pump flying capacitors (C₁, C₂, and C₃), one 1μF
ceramic input capacitor (C_IN), one 0.33μF to 1μF
ceramic capacitor for the backlight charge pump
output, and one 1μF for the flash charge pump out-
put. The six constant current sink inputs (D1 to D6)
can drive six individual LEDs with a maximum cur-
rent of 30mA each. The unused sink inputs must be
connected to V_{OUT_BL}, otherwise the part will operate
only in 2X charge pump mode. The AS²Cwire serial
interface enables the backlight charge pump and
sets the current sink magnitudes. AS²Cwire
addressing allows independent control of two
groups of current sink input: D1 to D4 and D5 to D6.
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