Analogictech tri-mode charge pump targets cell phone market

June 1, 2005
Date Announced: 01 Jun 2005 Meeting the demanding cost/performance standards of today’s mass market consumer cell phones, leading developer of innovative power management solutions AnalogicTech has introduced a high efficiency, low noise, constant frequency charge pump for white LED applications. The three-channel, tri-mode charge pump provides the right balance of functionality and silicon overhead to meet the commercial and functional standards that these highly competitive consumer applications require.Integrating a 1X load switch, 1.5X fractional and 2X doubling charge pump, the AAT3142 is optimized for the unique backlight power requirements of high-volume consumer cell phones with small, efficient colour displays.Tri-mode devices increase efficiency by stepping up voltage only when necessary. Since 80 percent of the discharge cycle of a lithium-ion/polymer battery is spent above the 3.5V threshold needed to drive white LEDs, constant use of a charge pump would waste energy. By integrating a 1X load switch, tri-mode devices like the AAT3142 allow the battery voltage to pass through to the output when sufficient voltage is available. The 1.5X and 2X charge pump modes are only activated when the battery power is low, allowing these devices to offer efficiency competitive to typical inductive boost converters.The AAT3142 produces 32 constant current levels up to 30mA for each output from a 2.7V to 5.5V input. The device uses AnalogicTech’s S2Cwire(TM) (Simple Serial Control(TM)) serial digital input to enable, disable, and set current for each LED. To reduce parts count and system footprint in compact portable devices, the AAT3142 uses a 1MHz switching frequency which enables the use of highly compact, 1µF external capacitors; two charge pump flying capacitors, one input capacitor, and one charge pump output capacitor.An integrated thermal management system protects the device if a short-circuit condition occurs at the output pin. Soft-start circuitry prevents excessive inrush current during startup. A low current shutdown feature reduces quiescent current to less than 1µA. Specified over the -40 to +85 degree centigrade temperature range, the AAT3142 is available immediately in a Pb-free, 12-pin TSOPJW package.

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

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