White LED drivers enable independent brightness control

National Semiconductor Corp. has introduced two highly integrated, charge-pump-based, constant-current white LED drivers for single- or multidisplay backlighting in portable consumer products and handsets. The LM27965 and LM27966 include an I?C-compatible interface that allows design engineers to independently control the brightness on each bank of LEDs.

The LM27965 can drive up to nine LEDs and the LM27966 can drive up to six LEDs in parallel, with a total output current of 180mA. Regulated internal current sinks deliver excellent current and brightness matching in all LEDs. The LED driver current sinks are split into two or three independently controlled groups. The primary group can be configured with four or five LEDs for backlighting a larger main display and the second group (LM27965 only) can be configured with two or three LEDs for backlighting a smaller secondary display. In addition, an independently controlled LED driver is provided for driving an indicator or general purpose LED.

National's LM27965 and LM27966 promise excellent efficiency without the use of an inductor by operating the charge pump in a gain of 3/2 or in Pass-Mode. The proper gain for maintaining current regulation is chosen based on the LED forward voltage so that efficiency is maximized over the input voltage range.

Key features for the LM27965 and LM27966 include: 91 percent peak LED drive efficiency; 25mm? total solution size; 0.3 percent current matching; resistor-programmable current settings; external chip RESET# pin; and, extended Li-ion input of 2.7-5.5V.

National's LM27965 and LM27966 are available now in 24-pin LLP packages that measure 4mm-by-4-by-0.8mm. The LM27965 costs $2.20 and the LM27966 costs $1.60 each in quantities of 1,000.