High Efficiency White LED Drivers
for Backlight and Keypad
General Description
The AAT1236 is a highly integrated, high efficiency
power solution for white LED and keypad backlights
in mobile/portable devices. It is based on a switching
boost converter which steps up the single cell lithi-
um-ion/polymer battery voltage to drive 5 strings of
series-connected white LEDs with precision current
regulation. The AAT1236 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.
A two-wire I C serial digital interface is used to indi-
vidually turn each output sink on/off and adjust the
LED current by group. Unlike conventional pulse
width modulation (PWM) control of LED brightness,
the AAT1236 drives the LEDs with constant, non-
pulsating current. The interface is fully compliant to
the Fast/Standard mode I
2
C specification, allowing a
transfer rate of up to 400kHz.
2
AAT1236
Features
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SwitchReg
™
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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
Two-Wire, I
2
C Compliant Serial Interface
— Two 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, 400kHz Serial Transfer Rate
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
A similar device is also available with a proprietary
Advanced Simple Serial Control™ (AS
2
Cwire™) sin-
gle wire interface; please see the AAT1235 datasheet.
The AAT1236 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.
Applications
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Digital Still Cameras (DSCs)
Keypad Backlight
Large Panel Displays
Mobile Handsets
PDAs and Notebook PCs
Personal Media Players
White LED Backlight
Keypad or
RGB LEDs
Typical Application
L=2.2µH
D1
Up to 24V max
C
OUT
2.2µF
Backlight
LEDs
Input :
2.7V~5.5V
C
IN
2.2µF
LIN
VIN
IN
SW
B1
B2
A1
A2
A3
OV
GND
AGND
R2
187kΩ
AAT1236
EN SDA SCL
RSET
R1
22.6kΩ
R3
12.1kΩ
Enable
I
2
C
Interface
SDA
SCL
1236.2007.02.1.1
1
AAT [ ADVANCED ANALOG TECHNOLOGY, INC. ]
