Advanced Analogic Technologies’ AAT1231 high-frequency, high-efficiency inductive boost dc-dc converter controls white LEDs in portable systems operating from single-cell lithium-ion/polymer batteries. Delivering 50 mA up to 24 V, it can drive 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 (S(2)Cwire) single-wire interface.
Traditional pulse-width modulation (PWM) techniques used to control series-connected LEDs can produce variations in current and therefore LED brightness. In addition, PWM control methods consume microcontroller processing resources, require general-purpose I/O interfaces, and demand additional components.
LED output current on the AAT1231 is controlled using the S(2)Cwire interface in 16 linear steps. By changing the feedback voltage with the SEL pin, designers can extend the output voltage another 16 levels. This lets designers “set and forget” the output across a total of 26 steps (after overlap) from 7.5% to 100%. Digital control improves display readability by providing flicker-free LED output.
The AAT1231’s high 2-MHz switching frequency provides fast response to load transients and permits the use of small external components, including a 2.2-µH inductor. Overall efficiency can be up to 82%. A true load disconnect feature completely isolates the load from the power source. By reducing leakage current to less than 1 µA, this function extends battery life and system standby time.
Specified from –40°C to 85°C, the AAT1231 is immediately available in a lead-free, 12-pin TSOPJW. The device costs $0.94 each in 1000-piece quantities.
Inductive Boost DC-DC Converter Powers Series-Connected White LEDs
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Steve Milano Leong -August 29, 2006
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