Power

Step-Up Converter drives LCD Backlight Plus Flash in portable devices

13th January 2006
ES Admin
0
Monolithic Power Systems' MP1529 is a single inductor step-up driver that can power 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 display backlighting or as many as 10 color LEDs for keypad backlighting. 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 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 0.5?A. 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: under voltage lockout; open circuit over voltage protection; cycle-by-cycle current limit; integrated soft-start and thermal shutdown.

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


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