AAT3156
High Efficiency 1X/1.5X/2X Charge Pump
For White LED Applications
General Description
The AAT3156 is a low noise, constant frequency
charge pump DC/DC converter that uses a tri-
mode load switch (1X), fractional (1.5X), and dou-
bling (2X) conversion to maximize efficiency for
white LED applications. The AAT3156 is capable of
driving six LED channels at a total of 180mA from
a 2.7V to 5.5V input. The current sinks may be
operated individually or in parallel for driving high-
er-current LEDs. A low external parts count (two
1µF flying capacitors and two small 1µF capacitors
at V
IN
and V
OUT
) make this part ideally suited for
small, battery-powered applications.
AnalogicTech's AS
2
Cwire™ (Advanced Simple
Serial Control™) serial digital input is used to
enable, disable, and set current for each LED with
a 16-level logarithmic scale plus four low-current
settings down to 50µA for optimized efficiency, with
a low housekeeping current of only 50µA.
Each output of the AAT3156 is equipped with built-in
protection for V
OUT
short circuit and auto-disable for
LED failure conditions. Built-in soft-start circuitry pre-
vents excessive inrush current during start-up. A low-
current shutdown feature disconnects the load from
V
IN
and reduces quiescent current to less than 1µA.
The AAT3156 is available in a Pb-free, space-saving,
thermally-enhanced 16-pin 4x4mm QFN package.
Features
•
•
ChargePump
™
•
•
•
•
•
•
•
•
•
•
•
V
IN
Range: 2.7V to 5.5V
Fully Programmable Current with Single Wire
— 16-Step Logarithmic Scale
— 15/20/30mA Max Current
— Four Low Current Settings Down to 50µA
— Low I
Q
(50µA) for Low Current Mode
Tri-Mode 1X, 1.5X, and 2X Charge Pump for
Maximum Efficiency and V
F
Coverage
Drives Six Channels of LEDs
Individual Main/Sub-Group Control
No Inductors, Low Noise Operation
1MHz Constant Switching Frequency
Small Application Circuit
Built-In Thermal Protection
Built-In Auto-Disable For Open Circuit
Automatic Soft Start
I
Q
<1µA in Shutdown
Thermally-Enhanced QFN44-16 Package
Applications
•
•
•
•
Color (RGB) Lighting
Programmable Current Sinks
White LED Backlighting
White Photo Flash for Digital Still Cameras
Typical Application
2.7V to 5.5V
C
IN
1µF
VIN
C1+
C1
1µF
C1-
C2+
AAT3156
C2-
VOUT
C2
1µF
D1
D2
D3
D4
D5
D6
C
OUT
1µF
EN/SET
EN/SET
D1
D2
D3
D4
D5
GND
D6
3156.2005.09.1.2
1
AAT [ ADVANCED ANALOG TECHNOLOGY, INC. ]
