The LTC3217 is an 850-kHz, high-efficiency 1X/1.5X/2X multimode charge pump that can drive multiple high-current LEDs in camera-phone applications. Utilizing constant-frequency operation for low noise, it can drive up to four LED current sources at up to 600 mA total output current, all from a compact 3- by 3-mm QFN package. Shutdown mode and current output levels are selected using two logic input pins.
Designed by Linear Technology Corp. (LTC), the LTC3217's voltage 2.9- to 4.5-V range is suited for single-cell Li-Ion inputs. When driven from a Li-Ion battery (3.6 V nominal), efficiencies reach 92%, maximizing battery run-time. It only requires four small capacitors and two resistors to create a low-profile solution.
The LTC3217 charge pump automatically optimizes efficiency based on Vin and LED forward voltage conditions. The device powers up in 1X mode and automatically switches to boost mode (1.5X) when any enabled LED current source approaches dropout; a subsequent dropout switches the part into 2X mode. Brightness is controlled by selecting each or both current set resistors through the enable inputs or by pulse-width modulation of the EN2 pin. Internal circuitry prevents in-rush current and excessive input noise during start-up and mode switching.
Pricing for the LTC3217EUD starts at $1.70 each for 1000-piece quantities. More information is available at www.linear.com.