Cell phone LED multi-display driver from Linear

July 21, 2004
Cell phone LED multi-display driver from Linear features 2-wire I2C interface and 92% efficiency
Linear Technology Corporation has announced the LTC3206, an 800 kHz, low noise, high efficiency step-up/step-down fractional charge pump voltage converter. It can drive a 1-6 LED main display, 1-4 LED sub-display plus an RGB display, all from a 4 x 4mm QFN package.
Linear LTC3206 Each display has digital control with independent dimming and programming via a two-wire I2C serial interface. The device's input voltage range of 2.8V to 4.5V optimizes it for single cell Li-Ion cellular applications. Driven from a single cell Li-Ion battery (3.6V), efficiencies reach 92% with quiescent current of only 180uA, maximizing battery run-time. The LTC3206 requires only four small capacitors and two resistors to create a tiny (<25mm2, 0.75mm high) solution footprint, capable of powering all LEDs used in three separate displays.

The LTC3206 charge pump optimizes efficiency based on VIN and LED forward voltage conditions. The device 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.

LED currents are controlled with internal current sources while dimming and ON/OFF control for all displays is achieved via a 2-wire I2C serial interface. Sixteen dimming states (logarithmic scale) are available for the main and sub displays, for a 128:1 dimming range. 16 dimming states are available through internal PWM for each of the red, green and blue LEDs, resulting in 4096 color combinations. Internal circuitry prevents inrush current and excessive input noise during start-up and mode switching.

The LTC3206EUF is available from stock in a 24-Lead QFN (4mm x 4mm) package. Pricing starts at $2.20 each for 1,000-piece quantities.

Summary of features: LTC3206

  • Up to 92% Efficiency without Inductors
  • Step-Up/Step-Down Fractional Charge Pump for Optimal Efficiency
  • Independent Current and Dimming Control for 1-6 Main, 1-4 Sub and RGB Displays
  • LED Currents Programmed Using a 2-Wire I²C Serial Interface
  • <0.7% LED Current Matching Error
  • Low Noise, Constant Frequency Operation
  • 2.7V to 4.5V Input Voltage Range
  • Tiny Solution Footprint, <25mm², <0.75mm Profile
  • 4 x 4mm QFN-24 Package