High Efficiency White LED Drivers
for Backlight and Keypad
General Description
The AAT1235 is a highly integrated, high efficiency
power solution for white LED backlight and keypad
backlights in mobile/portable devices. It is based on a
switching boost converter which steps up the single-
cell lithium-ion/polymer battery voltage to drive 5
strings of series-connected white LEDs with preci-
sion current regulation. The AAT1235 is capable of
driving a total of four LEDs per channel.
The boost converter can produce an output drive of
up to 24V at 100mA. The high switching frequency
(up to 2MHz) provides fast response to load tran-
sients and allows the use of small external compo-
nents. A fully integrated control circuit simplifies the
design and reduces total solution size.
AnalogicTech's Advanced Simple Serial Control™
(AS
2
Cwire™) serial digital input is used to individual-
ly turn each output sink on/off and adjust the LED
current by group. Unlike conventional pulse width
modulation (PWM) control of LED brightness, the
AAT1235 drives the LEDs with constant, non-pulsat-
ing current.
A similar device is also available with an I
2
C two-
wire interface; please see the AAT1236 datasheet.
The AAT1235 is available in a Pb-free, thermally-
enhanced 16-pin 3x4mm TDFN package and is
specified for operation over the -40°C to +85°C tem-
perature range.
AAT1235
Features
•
•
•
•
•
•
SwitchReg
™
•
•
•
•
Input Supply Voltage Range: 2.7V to 5.5V
Maximum Boost Output Drive: Up to 24V at 100mA
Up to 85% Efficient Operation
Up to 2MHz Switching Frequency with Small
Inductor
User-Programmable Full-Scale LED Current, Up
to 30mA
Single-Wire AS
2
Cwire Serial Interface
— Five Addressable Registers
• Independent LED Current Control by Group
— Backlight Group B1-B2, 16 Settings
— Auxiliary Group A1-A3, 16 Settings
• Independent LED ON/OFF Control
— Fast, 1MHz Serial Interface
Non-Pulsating, High-Performance LED Current
Drive for Uniform Illumination
— 10% Absolute Accuracy
— 2% Channel-to-Channel Matching
Over-Voltage and Over-Temperature Protection
Automatic Soft-Start Minimizes Large Inrush
Current at Startup
Available in 3x4mm TDFN34-16 Package
Applications
•
•
•
•
•
•
•
Digital Still Cameras (DSCs)
Keypad Backlight
Large Panel Displays
Mobile Handsets
Personal Media Players
PDAs and Notebook PCs
White LED Backlight
Typical Application
L = 2.2µH
D1
Up to 24V Max
Keypad or
RGB LEDs
C
OUT
2.2µF
Backlight
LEDs
LIN
Input :
2.7V~5.5V
C
IN
2.2µF
VIN
IN
EN/SET
SW
B1
B2
A1
A2
A3
OV
R2
187kΩ
AAT1235
RSET
R1
22.6kΩ
GND
AGND
R3
12.1kΩ
AS
2
Cwire Control
1235.2007.02.1.1
1
ANALOGICTECH [ ADVANCED ANALOGIC TECHNOLOGIES ]
