Charge pumps go three ways for handset LED power

Edited by the Electronicstalk editorial team Apr 10, 2006

Highly integrated 850kHz low-noise high-efficiency 1x/1.5x/2x multimode charge pumps drive main, camera and auxiliary LED displays in cellular phones.

Linear Technology has announced the LTC3209-1 and LTC3209-2, highly integrated 850kHz low-noise high-efficiency 1x/1.5x/2x multimode charge pumps for driving main, camera and auxiliary LED displays in cellular phones.

They can each drive up to eight LED current sources at up to 600mA of total output current.

The LTC3209-1 can drive up to a six-LED main display, a one-LED camera display, and a one-LED auxiliary display, whereas the LTC3209-2 can drive up to a five-LED main display, a two-LED camera display, and a one-LED auxiliary display, all from a compact 4 x 4mm QFN package.

Each display has digital control with independent dimming and programming via a two-wire I2C serial interface.

The LTC3209-1/-2's input voltage range of 2.9 to 4.5V has been optimised for single cell Li-ion cellular applications.

Efficiencies when driven from a Li-ion battery (3.6V nominal) reach 94% with quiescent current of only 400uA, maximising battery run-time.

Both the LTC3209-1/-2 require only four small capacitors and one resistor to create a tiny, low profile (less than 25mm2, 0.75mm high) solution footprint.

The LTC3209-1 and LTC3209-2 charge pumps feature low-noise constant-frequency operation and automatically optimise efficiency based on VIN and LED forward voltage conditions.

The devices power up in 1x mode and automatically switch to boost mode (1.5x) when any enabled LED current source approaches dropout; a subsequent dropout switches the parts into 2x mode.

Maximum currents for the main/cam/aux displays are set with a single resistor.

LED currents are controlled with precision internal current sources while dimming and on/off control for all displays are achieved via a two-wire I2C serial interface.

256 brightness levels are available for the main display, 16 for the camera display, and four for the auxiliary display.

Internal circuitry prevents inrush current and excessive input noise during startup and mode switching.

In addition, the device has short circuit, thermal and open/short LED protection.

The LTC3209EUF-1 and LTC3209EUF-2 are available from stock in a 20-lead QFN package.

Pricing starts at $1.80 each for 1000-piece quantities.