AAT3131_08 ANALOGICTECH [Advanced Analogic Technologies], AAT3131_08 Datasheet - Page 7

• Manufacturer Part Number: AAT3131_08
• Description: High Efficiency 1X/1.5X Fractional Charge Pump for White LED Applications
• Manufacturer: ANALOGICTECH [Advanced Analogic Technologies]

Functional Block Diagram
Functional Description
The AAT3131 is a dual mode load switch (1X) and
high efficiency (1.5X) fractional charge pump
device intended for white LED backlight applica-
tions. The fractional charge pump consists of a low
dropout linear voltage regulator followed by a 1.5X
charge pump with multiple current-source outputs.
To maximize power conversion efficiency, an inter-
nal feedback control sensing circuit monitors the
voltage required on the constant current source
outputs.
switch and charge pump functions based upon the
input voltage level versus the output voltage level
needed. This function significantly enhances over-
all device efficiency when the input voltage level is
greater than the voltage required at the constant
current source outputs. The 1X load switch/1.5X
charge pump mode decision is based on the volt-
age levels sensed on either the D1 output or the
D4 output, whichever is greater. Switchover
3131.2005.12.1.2
This control circuit then sets the load
EN/SET
Interface
S
2
Cwire
Charge Pump for White LED Applications
Reference
32x16 bit
32x16 bit
Reference
Soft-Start
Oscillator
Current
Voltage
Control
1MHz
ROM
ROM
High Efficiency 1X/1.5X Fractional
GND
between the 1.5X (charge pump) operating mode
and the 1X (load switch) mode occurs automatical-
ly (as a function of input and output voltages) and
does not require user intervention to maintain max-
imum efficiency.
The AAT3131 requires only four external compo-
nents: two 1µF ceramic capacitors for the charge
pump flying capacitors (C
ceramic input capacitor (C
1µF ceramic output capacitor (C
LDO/1.5X charge pump output is converted into
three (D1 to D3) constant current outputs to drive
three individual LEDs with a maximum current of
20mA each, and one (D4) constant current output
with a maximum current of 30mA. The current
source output magnitude is controlled by the
EN/SET serial data interface. The interface records
rising edges of the EN/SET pin and decodes them
into 32 addresses corresponding to individual cur-
rent level settings. The 32 addresses are divided
1X/1.5X
Charge
Output
Output
VIN
Single
Pump
Quad
DAC
DAC
C1+
C1-
C2+
C2-
OUT
D1
D2
D3
D4
IN
1
), and one 0.33µF to
and C
AAT3131
2
), one 1µF
OUT
). The
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