AnalogicTech charge pump enables continuous backlighting

May 11, 2005
Date Announced: 11 May 2005 Developer of innovative power management solutions AnalogicTech has introduced a multi-function, high efficiency, dual charge pump that is super efficient in low-current mode, delivering extremely low quiescent current and allowing designers to continually backlight displays while consuming minimal amounts of power. Many portable devices using different display types, and (particularly) transmissive displays require some minimal level of backlighting at all times.AnalogicTech’s AAT2805 supports both white LED backlight and camera flash applications for portable systems that run on lithium-ion/polymer batteries. Featuring a light load mode with quiescent current as low as 80µA (typical), the AAT2805 minimises power consumption during backlight operation.The backlight charge pump in the AAT2805 drives up to four LEDs at a total output of 120mA. Current sinks may be operated individually or in parallel to drive higher current LEDs. To maximise power efficiency, the charge pump operates in 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. Optimised current sinks minimize the voltage headroom required to drive each LED and help increase the amount of time the device stays in 1X mode before transitioning to 1.5X charge pump mode. That capability, in turn helps to maximise power efficiency.Using AnalogicTech’s Advanced Simple Serial Control™ (AS2Cwire™) 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 light load mode down to 50µA (typical).For flash applications, the AAT2805 integrates a charge pump doubler with a regulated output voltage. It is capable of delivering up to 120mA of continuous current for ‘movie-mode’ or up to 250mA of pulsed current for camera flash. An independent enable pin maximises power savings. A built-in thermal management circuit protects the device and soft-start circuitry prevents excessive inrush current during start-up. The AAT2805’s high, 1MHz charge pump switching frequency allows designers to support the device with extremely small ceramic capacitors. By eliminating the use of inductors, the AAT2805 also allows designers to build smaller, lower-profile systems.AnalogicTech’s versatile AAT2805 is available in a 16-pin, thermally-enhanced, lead-free TDFN44 package and is qualified across the 40 to +85 degree C temperature range.

Phil Dewsbury Advanced Analogic Technologies, Inc., Europe 1210 Parkview, Theale, Berkshire, RG7 4TY Tel: +44 (0) 1189 657763

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