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DC/DC converter surpasses PWM technique for LED control

Posted: 28 Jul 2006     Print Version  Bookmark and Share

Keywords:AnalogicTech  AAT1231  boost DC/DC converter 

Advanced Analogic Technologies Inc. (AnalogicTech) has announced the AAT1231, a high-frequency, high-efficiency inductive boost DC/DC converter for controlling white LEDs in portable systems operating from single-cell Li-ion/polymer batteries. The company said the product has surpassed the former de facto standard PWM technique to control series-connected LEDs.

Delivering 50mA up to 24V, AnalogicTech said this new device is capable of driving up to six white LEDs in series or up to 12 white LEDs in a parallel/series configuration using the company's digital Simple Serial Control (S2Cwire) single-wire interface. This enables designers to use a single wire to digitally control white LEDs, giving flicker-free light output, reduced MCU clock cycles and saving in GPIO resources.

PWM produces variations in current that affect LED brightness. The control methods required for the old technique also consume microcontroller processing resources, require GPIO interfaces, and demand a large number of additional components. AnalogicTech said AAT1231 addresses all these.

LED output current on the device is controlled using S2Cwire interface in 16 linear steps. By changing the feedback voltage with the SEL pin, designers can extend the output voltage another 16 levels. This allows them to "set and forget" the output across a total of 26 steps (after overlap) from 7.5 per cent to 100 per cent. Digital control improves display readability by providing constant flicker-free LED output.

According to AnalogicTech, the device's 2MHz switching frequency provides fast response to load transients and permits the use of small external components including a 2.2μH inductor. It promises an overall efficiency up to 82 per cent. The device also adds a true load disconnect feature that completely isolates the load from the power source. By reducing leakage current to less than 1μA, the company said this function extends battery life and system standby time.

The AAT1231 also offers a wide variety of standard protection features, including integrated soft-start, current limit, over-temperature and over-voltage protection. Specified over the -40°C to 85°C temperature range, the device is immediately available in a Pb-free, 12-pin TSOPJW package.

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