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Linear Tech voltage converter drives multiple displays

Posted: 11 Aug 2004 ?? ?Print Version ?Bookmark and Share

Keywords:linear technology? voltage converter? ltc3206?

Linear Technology Corp. developed an 800kHz, low noise, high efficiency step-up/step-down fractional charge pump voltage converter that can drive a 1-6 LED main display and 1-4 LED sub-display plus an RGB display, all from a 4-by-4mm QFN package. Each display has digital control with independent dimming and programming via a two-wire I?C serial interface.

The LTC3206's input voltage range of 2.8V to 4.5V makes it suitable for single cell Li-ion cellular applications. Driven from a single cell Li-ion battery (3.6V), efficiencies reach 92 percent with a quiescent current of 180?A. The device requires only four small capacitors and two resistors to create a tiny (<25mm?, 0.75mm high) solution footprint, capable of powering all LEDs used in three separate displays.

The charge pump optimizes efficiency based on VIN and LED forward voltage conditions. It powers up in step-down mode and only switches to step-up mode when any enabled LED current source approaches dropout. Maximum currents for the main/sub/RGB displays are set with a single resistor, while the LED currents are controlled with internal current sources, and the dimming and ON/OFF control for all displays is achieved via a 2-wire I?C serial interface. Sixteen dimming states (logarithmic scale) are available for the main and sub displays, for a 128:1 dimming range. The 16 dimming states are available through internal PWM for each of the Red, Green and Blue LEDs, resulting in 4,096 color combinations. Internal circuitry prevents inrush current and excessive input noise during start-up and mode switching.

Pricing starts at $2.20 each in 1,000-piece orders.

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