Multimode charge pump features low-noise constant-frequency operation, automatically optimising efficiency based on the voltages across the LED current sources.
T
he LTC3220/-1 is an inductorless low-noise high-efficiency LED driver for cellphone displays and other programmable lighting applications. The Linear Technology IC provides 18 individually configurable LED current sources for complete flexibility in programming multiple displays. The display currents are set via a precision internal current reference.
The universal current sources can be digitally controlled with independent dimming, brightness, blinking, and gradation control, programmable via a simple two-wire I2C serial interface; the LTC3220 and LTC3220-1 each offer a unique I2C address.
The LTC3220/-1's 2.9 to 5.5V input voltage range has been optimised for single-cell Li-ion/polymer battery applications. Efficiencies when driven from a lithium battery (3.6V nominal) reach 91%, with quiescent current as low as 500uA, maximising battery runtime.
Furthermore, slew-rate limited switching reduces conducted and radiated noise (EMI).
The LTC3220/-1's multimode charge pump features low-noise constant-frequency operation, automatically optimising efficiency based on the voltages across the LED current sources.
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 device into doubler (2x) mode. Internal circuitry prevents inrush current and excessive input noise during start-up and mode switching.
In addition, the device has short circuit and thermal protection.
The LTC3220/-1 is available from stock in the ultra-thin (0.55mm) 28-lead QFN (4 x 4mm) package. The IC requires only five small capacitors for a tiny, complete LED power supply and current controller solution. Pricing starts at US $2.35 each for 1000-piece quantities.
