AAT3155
High Efficiency 1X/1.5X/2X Charge Pump
For White LED Applications
3155.2006.05.1.1 1
ChargePump
™
General Description
The AAT3155 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 AAT3155 is capable of
driving up to four channels of LEDs at 20mA per
channel from a 2.7V to 5.5V input. The current
sinks may be operated individually or in parallel for
driving higher current LEDs. A low external parts
count (two 1µF flying capacitors and two small 1µF
capacitors at IN and OUTCP) make this part ideal-
ly suited for small, battery-powered applications.
AnalogicTech's S
2
Cwire
™
(Simple Serial Control
™
)
serial digital input is used to enable, disable, and set
current for each LED with 16 settings down to 50µA.
The low-current mode supply current can be as low
as 50µA to save power.
Each output of the AAT3155 is equipped with built-
in protection for output short-circuit and auto-dis-
able for load short-circuit conditions. Built-in soft-
start circuitry prevents excessive inrush current
during start-up. A low-current shutdown feature dis-
connects the load from the input and reduces qui-
escent current to less than 1µA.
The AAT3155 is available in a Pb-free, space-sav-
ing 2.85x3.0mm 12-pin TSOPJW package.
Features
•V
IN
Range: 2.7V to 5.5V
• Fully Programmable Current with Single Wire
— 16 Current Levels
— 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 up to Four Channels of LEDs
• No Inductors, Low Noise Operation
• 1MHz Constant Switching Frequency
• Small Application Circuit
• Built-In Thermal Protection
• Automatic Soft Start
•I
Q
<1µA in Shutdown
• 2.85x3.0mm TSOPJW-12 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
EN/SET
IN
EN/SET
C2+
C2-
C1+
C1-
OUTCP
D1
D2
D3
GND
AAT3155
D1
C1
1µF
C2
1µF
C
IN
1µF
C
OU T
1µF
D2 D3 D4
D4