High Efficiency 1.5X Fractional Charge
Pump For White LED Applications
General Description
The AAT3194 is a low noise, constant frequency
charge pump DC/DC converters that use fractional
(1.5X) conversion to increase efficiency in white
LED applications. The devices can be used to pro-
duce current levels up to 20mA for each output
from a 2.7V to 5.5V input. A low external parts
count (two 1µF flying capacitors and two small
bypass capacitors at IN and OUT) makes these
devices 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 for 32-level logarithmic scale LED
brightness control. The AAT3194 has a thermal
management system for protection 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. A high switching frequency
enables the use of small external capacitors. A low-
current shutdown feature disconnects the load from
V
IN
and reduces quiescent current to less than 1µA.
The AAT3194 is available in a Pb-free 12-pin
TSOPJW package.
AAT3194
Features
•
•
•
•
•
•
•
•
•
•
•
•
•
•
ChargePump
™
V
IN
Range: 2.7V to 5.5V
20mA Full-Scale Current
Simple Serial Control (S
2
Cwire) Interface
— 32-Position Logarithmic Scale with Digital
Control
Low Noise Constant Frequency Operation
33% Less Input Current Than Doubler
Charge Pump
High Accuracy Brightness Matching
Small Application Circuit
Regulated Output Current
Automatic Soft Start
No Inductors
600kHz Switching Frequency
I
Q
<1µA in Shutdown
Temperature Range: -40°C to 85°C
12-Pin TSOPJW Package
Applications
•
•
Programmable Current Source
White LED Backlighting
Typical Application
IN
C1+
C1
1µF
OUT
V
BATTERY
C
IN
1µF
C
OUT
1µF
C1-
C2+
C2
1µF
AAT3194
C2-
D1
D2
D3
EN/SET
EN/SET
GND
D4
D4
D3
D2
D1
3194.2006.09.1.0
1
ANALOGICTECH [ ADVANCED ANALOGIC TECHNOLOGIES ]
