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White LED driver promises up to 55% power saving

Posted: 27 Aug 2009 ?? ?Print Version ?Bookmark and Share

Keywords:LED driver? white LED? backlight?

LM3530 LED driver

National Semiconductor Corp. claims the smallest white LED driver with dynamic display backlight control that drives up to 11 high-current LEDs in series, illuminating larger displays in portable media devices such as smart phones. . The LM3530, a member of National's PowerWise energy-efficient product family, is offered in a 12-bump micro SMD package measuring just 1.615mm x 1.215mm x 0.425mm.

The increased multimedia content in portable devices is fueling the trend towards larger displays and longer video playback, which require more power. The LM3530 LED driver employs ambient light-sensing algorithms and content-adjustable backlighting to optimize the display, realizing up to a 55 percent power saving over the common practice of driving the backlight at a constant brightness.

In a pair of tests, National compared the energy consumption of a backlight illuminating a 3.5-inch iPod touch display with and without National's LM3530 LED driver.

The evaluation was conducted using typical multimedia downloadable material, in this case an episode from a television series and a trailer from a popular movie. Results showed the LM3530 achieved a power savings of 43 percent and 55 percent, respectively, over traditional backlighting. The predominately darker picture in the movie trailer garnered further power savings because the backlight was reduced more frequently for dark images.

National's LM3530 current-mode boost converter can supply up to 29.5mA of power to 11 white LEDs from a single-cell Li-ion battery. A wide degree of programmability via an I?C compatible interface enables the designer to adjust for lighting effects such as fading, external ambient conditions and lighting level, as well as brightness and image performance.

The LM3530's programmable ambient light response along with a separate pulse-width modulation dimming input enable the backlight LED driver to intelligently determine lighting requirements and select between various dimming options, optimizing the light output for the given conditions. Logarithm and linear LED brightness mapping provides flicker-free dimming. A fixed-frequency, 500 kHz boost converter provides high efficiency over the LED current range.

The LM3530 brings power savings to the serial implementation of large display backlighting. For parallel charge pumps, National will offer a product with a similar feature set in October 2009.

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