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Charge-pump saves power

Posted: 12 May 2005 ?? ?Print Version ?Bookmark and Share

Keywords:advanced analogic technologies? aat2805? dual charge-pump?

Emphasizing minimum power consumption for display backlighting, Advanced Analogic Technologies' AAT2805 is a dual charge-pump that also supports camera flash applications.

"Many portable devices using different display types, particularly transmissive displays, require some minimal level of backlighting at all times," explained Jan Nilsson, VP of sales and marketing. "The AAT2805 is super efficient in low-current mode, delivering extremely low quiescent current which allows designers to continually backlight their displays while consuming minimal amounts of power."

The device's backlight charge-pump delivers up to 120mA for driving up to four LEDs. Current sinks may be operated individually or in parallel to drive higher current LEDs. To maximize power efficiency, the charge-pump operates in the 1x, 1.5x, and 2x modes. The device automatically selects the most efficient mode by comparing the forward voltage of each LED with the input voltage. Optimized current sinks minimize the voltage headroom required to drive each LED and help increase the amount of time the pump stays in its 1x mode before transitioning to the 1.5x mode.

Using the company's Advanced Simple Serial Control (AS?Cwire) digital interface, the device enables, disables, and sets current for each LED across a 16-level logarithmic scale. Four low-current settings allow operation in a "light-load" mode down to 50?A (typical).

The AAT2805 also includes a charge-pump doubler with a regulated output voltage for flash applications. The pump delivers up to 120mA of continuous current for "movie-mode" applications, or up to 250mA of pulsed current for camera flash. An independent enable pin maximizes power savings. A built-in thermal management circuit protects the device and soft-start circuitry prevents excessive inrush current during start-up. The backlighting charge-pump's 1MHz switching frequency allows use of extremely small ceramic capacitors.

The device's data sheet is available from the company's website. The AAT2805, available in a 16-pin, thermally-enhanced, Pb-free TDFN44 package and qualified across the -40C to 85C range, sells for $1.64 each in 1k quantities.

- Vincent Biancomano


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