Integrated White LED Driver from National

National Semiconductor Corp. (Santa Clara, CA) has introduced a small dual step-up DC-DC converter that drives up to five white LEDs with a constant current or an organic LED display with a constant voltage. The LM3520 is well-suited for handheld devices such as flip and clam-shell cellular phones and digital cameras.

The LM3520 step-up converter uses pulse width modulation (PWM) mode to drive the LEDs and pulse frequency modulation (PFM) mode to drive the organic LED display. This allows the best performance combination of high efficiency and stability. When driving the LEDs, a single external resistor is used to set the maximum LED current. The actual LED current and the brightness can be adjusted by applying a PWM signal to the enable pin. When the LED drive is disabled, the LED string is disconnected on the low side so that there is no leakage current through the LEDs.

Some features of the LM3520 include: Higher than 80 percent peak efficiency; Drives up to 5 LEDs at 20 mA/3.6V and 4 LEDs at 30 mA/3.6V for the main display; Up to 20V at 50 mA/3.6V for the sub-display; true shutdown isolation; 1 MHz switching frequency; 23V of over-voltage protection; wide input voltage range of 2.7V to 5.5V; cycle-by-cycle current limit; and PWM dimming control.

National's LM3520 is available now in a small, low-profile 14-pin LLP® package that measures 3 mm x 4 mm x 0.8 mm and costs $2.60 in quantities of 1,000. Lead-free package options are also available.