Step up driver powers LED strings three ways

A Monolithic Power Systems (MPS) product story

Edited by the Electronicstalk editorial team Dec 8, 2005

The MP1529 is a single-inductor step-up driver that is capable of powering three LED strings from a single lithium-ion battery.

Monolithic Power Systems has announced the MP1529, a single-inductor step-up driver that is capable of powering three LED strings from a single lithium-ion battery, making it one the most highly integrated LED drivers for portable electronics.

From an input voltage of 2.7V, two similar current strings (up to 30mA) can comprise six white LEDs suitable for LCD backlighting or as many as 10 colour LEDs for keypad backlighting.

(This is because colour LEDs have a lower forward voltage than white LEDs).

The third string (up to 150mA) can consist of four white LEDs suitable for a high power white LED camera flash application.

This MP1529 incorporates a 250mW power FET to support operation in four modes: shutdown, backlight, preview and flash - the latter two modes targeted specifically at digital camera functionality.

In backlight mode, just the two backlight strings are illuminated.

In preview mode the two backlight strings remain lit while the flash string is illuminated to allow for verification of composition and exposure of the shot.

In flash mode the two backlight strings are turned off with full power diverted to the flash string.

In shutdown, driver current is removed from all three strings and quiescent current drops to 0.5mA.

Current levels for backlight, preview and flash mode are set with the use of three external resistors.

A two-pin digital enable interface selects between the three modes and device shutdown.

The two backlight LED strings may be dimmed by applying a PWM signal to the EN1 pin.

The flash string is not affected by the dimming signal and will maintain brightness in that mode.

In-built protection features include: undervoltage lockout; open circuit overvoltage protection; cycle-by-cycle current limit; integrated soft-start; and thermal shutdown.

Targeted at applications including PDAs, cellphones and digital cameras, the MP1529 is available in a tiny 16-pin 4 x 4mm package.