Document
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 lithium-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 transients and allows the use of small external components. A fully integrated control circuit simplifies the design and reduces total solution size. A two-wire I2C serial digital interface is used to individually 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, nonpulsating current. The interface is fully compliant to the Fast/Standard mode I2C specification, allowing a transfer rate of up to 400kHz. A similar device is also available with a proprietary Advanced Simple Serial Control™ (AS2Cwire™) single wire interface; please see the AAT1235 datasheet. The AAT1236 is available in a Pb-free, thermallyenhanced 16-pin 3x4mm TDFN package and is specified for operation over the -40°C to +85°C temperature range.
AAT1236
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 Two-Wire, I2C 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
Applications
• • • • • • • 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 CIN 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 I2C Interface SDA SCL
1236.2007.02.1.1
1
High Efficiency White LED Drivers for Backlight and Keypad Pin Descriptions
Pin #
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 EP
AAT1236
Symbol
VIN OV EN B1 B2 RSET IN GND SW SDA SCL AGND A3 A2 A1 LIN
Function
Input supply for the converter. Connect a 2.2µF or larger ceramic capacitor from VIN to GND. Boost output over voltage detect pin. Use resistor divider to set the circuit's external overvoltage protection. See Applications Information for details. Enable pin. Backlight current sink 1. Connect the cathode of the last LED in the string to B1. Backlight current sink 2. Connect the cathode of the last LED in the string to B2. LED current set resistor. A 22.6kΩ resistor from RSET to AGND sets the maximum LED current in A1-A3 and B1-B2 to 20mA. Input bias supply for the internal circuitry. Connect IN to VIN directly at the AAT1236. Power ground for the boost converter. Connect GND to AGND at a single point as close to the AAT1236 as practical. Boost converter switching node. A 2.2µH inductor, connected between SW and LIN, sets the boost converter's switching frequency. I2C interface serial data line. I2C interface serial clock line. Ground pin. Connect AGND to GND at a single point as close to the AAT1236 as practical. Auxiliary current sink 3. Connect the cathode of the last LED in the string to A3. Auxiliary current sink 2. Connect the cathode of the last LED in the string to A2. Auxiliary current sink 1. Connect the cathode of the last LED in the string to A1. Switched power input. Connect LIN to the external power inductor. Exposed paddle (bottom). Connected internally to SW. Connect to SW or leave floating.
Pin Configuration
TDFN34-16 (Top View)
VIN OV EN B1 B2 RSET IN GND
1 2 3 4 5 6 7 8
16 15 14 13 12 11 10 9
LIN A1 A2 A3 AGND SCL SDA SW
2
1236.2007.02.1.1
High Efficiency White LED Drivers for Backlight and Keypad Absolute Maximum Ratings1
TA = 25°C unless otherwise noted. Symbol
VIN, IN SW EN, SCL, SDA, Bx, Ax, RSET, OV, LIN TS TJ TLEAD
AAT1236
Description
Input Voltage Switching Node Maximum Rating Storage Temperature Range Operating Temperature Range Maximum Soldering Temperature (at leads, 10 sec)
Value
-0.3 to 6.0 28 VIN + 0.3 -65 to 150 -40 to 150 300
Units
V V V °C °C °C
Thermal Information2
Symbol
θJA PD
Desc.