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High efficiency boost converters for large panel WLED applications from AnalogicTech

31st January 2007

Advanced Analogic Technologies Inc., Europe

ES Admin

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In large-panel lighting applications, uniform illumination using multiple strings of series-connected WLEDs is a very difficult design objective to meet. Many existing solutions rely on PWM techniques that, using a modulating DC input voltage, produce substantial flicker. With AnalogicTech’s AAT1235 and AAT1236, designers can now employ a single boost converter with a digital interface to run five 20mA strings of up to four series-connected WLEDs and deliver a constant, non-pulsating forward current ensuring uniform brightness across the entire display, simultaneously reducing component count and simplifying design.

Targeted at WLED applications for large format LCD screens, the AAT1235 and AAT1236 boost converters offer a high efficiency, high voltage power source in a single package. The devices’ five strings are split into two banks, one comprised of two current sinks for backlight applications and a second comprised of three current sinks for auxiliary lighting functions. Each bank of strings can be turned on or off independently or as a whole.

The two boost converters also offer designers substantial space savings. By integrating the driver and control line for multiple series-connected WLED strings into one circuit, the devices eliminate multiple discrete drivers, inductors, capacitors, resistors and diodes. Furthermore, by operating at a high 2MHz switching frequency, the devices also support the use of extremely small footprint 2.2 micro Henry inductors.

Operating from a 2.7 to 5.5V input, the AAT1235 and AAT1236 supply a maximum boost output of 24V at 100mA. The two backlight LED current sinks and the three output auxiliary lighting current sinks can be driven up to 30mA each using 16 user-programmable levels.

The AAT1235 features AnalogicTech’s Advanced Simple Serial Control (AS2Cwire) serial digital control to turn on and off each output sink and adjust LED current by group. The AAT1236 boost converter offers the same features as the AAT1235, but with an I2C interface for configuration and control. Both devices also feature automatic soft start, overvoltage and over-temperature protection.

The AAT1235 and AAT1236 are specified across the -40 to +85 degrees C temperature range. They are available in a Pb-free, thermally enhanced, 16-pin TDFN34 packages.