High Efficiency 1X/1.5X Fractional
Charge Pump for White LED Applications
General Description
The AAT3131 is a low noise, constant frequency
charge pump DC/DC converter that uses a dual
mode Load Switch (1X) and fractional (1.5X) con-
version to maximize efficiency for White LED appli-
cations. The device can be used to produce cur-
rent levels up to 20mA in three of its outputs, and
30mA in one of its outputs to drive LEDs from a
2.7V to 5.5V input. Outputs may be operated indi-
vidually or paralleled for driving higher-current
LEDs. Low external parts counts (two 1µF flying
capacitors and two small 1µF capacitors at V
IN
,
and OUT) make the AAT3131 ideally suited for
small battery-powered applications.
AnalogicTech™'s Simple Serial Control™
(S
2
Cwire™) interface is used to enable, disable
and set the LED drive current in two groups: the
three 20mA outputs and the single 30mA output
with multiple level logarithmic scales. The AAT3131
has a thermal management system to protect the
device in the event of a short circuit condition at the
output pin. Built-in soft-start circuitry prevents
excessive inrush current during start-up. A high
charge pump switching frequency enables the use
of very small external capacitors. A low current
shutdown feature disconnects the load from V
IN
and reduces quiescent current to less than 1µA.
The AAT3131 is available in very small 12 pin
TSOPJW12 package.
AAT3131
Features
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ChargePump
™
V
IN
Range: 2.7 - 5.5 Volts
< 1.0µA of Shutdown current
1.0 MHz Switching Frequency
White LED Backlighting
Fully Independent Display Lighting
Dual Mode 1x and 1.5x Charge Pump for
Maximum Efficiency
Drives Low-V
F
& High-V
F
f Type LED's
Up to three 20mA Outputs
Single 30 mA Output
Multi Position Logarithmic Scale with Digital
Control
Low Noise Constant Frequency Operation
Regulated Output Current
Automatic Soft-Start
No Inductors
-40 to +85°C Temperature Range
12 pin TSOPJW-12 package
Applications
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White LED Backlighting
White Photo-Flash for DSC's
Color (RGB) Lighting
Programmable Current Source
Typical Application
V
IN
C1+
C1
1µF
V
OUT
V
BATTERY
C
IN
1µF
C
OUT
1µF
C1-
C2+
C2
1µF
AAT3131
C2-
D1
D2
D3
D4
EN/SET
EN/SET
D5
GND
D4
D3
D2
D1
3131.2004.08.1.1
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ANALOGICTECH [ ADVANCED ANALOGIC TECHNOLOGIES ]
