AAT3122
High Efficiency 1X/1.5X Fractional Charge
Pump for White LED Applications
General Description
The AAT3122 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 increase efficiency in white LED applica-
tions. With input voltages ranging from 2.7V to
5.5V, the device can produce an output current of
up to 120mA. A low external parts count (two 1µF
flying capacitors and two small bypass capacitors
at V
IN
and OUT) makes the AAT3122 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 with a 32-level logarithmic scale
LED brightness control. The AAT3122 has a ther-
mal management system to protect the device in
the event of a short-circuit condition on any of the
output pins. Built-in soft-start circuitry prevents
excessive inrush current during start-up. High
switching frequency enables the use of small exter-
nal capacitors. A low shutdown current feature dis-
connects the load from V
IN
and reduces quiescent
current to less than 1µA. The AAT3122 provides a
single current source output that can be used to
drive up to six LEDs at 20mA each. The AAT3122
is available in a Pb-free TSOPJW-12 package.
Features
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ChargePump
™
V
IN
Range: 2.7V to 5.5V
<1µA of Shutdown Current
1 MHz Switching Frequency
Dual Mode 1X and 1.5X Charge Pump for
Maximum Efficiency
Only Four External Components
Simple Serial Control (S
2
Cwire) Interface
Low Noise Constant Frequency Operation
33% Less Input Current Than Doubler Charge
Pumps
Small Application Circuit
Regulated Output Current
Automatic Soft Start
No Inductors
TSOPJW-12 Package
-40°C to +85°C Temperature Range
Applications
•
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Programmable Current Source
White LED Backlighting
Typical Application
V
IN
C1+
C1
1µF
AAT3122
V
OUT
V
BATTERY
C
IN
1µF
C
OUT
1µF
C2-
EN/SET
EN/SET
GND
D
C1-
C2+
C2
1µF
D1
D2
D3
D4
D5
D6
3122.2005.11.1.3
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AAT [ ADVANCED ANALOG TECHNOLOGY, INC. ]
