National Semiconductor recently 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 I²C compatible interface that allows the design engineer 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 180 mA. Regulated internal current sinks deliver current and brightness matching in all LEDs. They 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.
These devices provide 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 maximised over the input voltage range.
Key features for the LM27965 and LM27966 include: 91% peak LED drive efficiency; no inductor required; 0,3% current matching; drives LEDs with up to 30 mA per LED; 180 mA total drive current; I²C compatible brightness control interface; resistor-programmable current settings.
National's LM27965 and LM27966 operate on 2,7 V to 5,5 V and are available in 24-pin LLP packages that measure 4 x 4 x 0,8 mm.
For more information contact Lambert Colyn, Arrow Altech Distribution, +27 (0)11 923 9600, [email protected]
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