Power Electronics

White LED Driver

THE LM3530 white LED driver from National Semiconductor Corp. is said to be the industry's smallest such device to offer dynamic display backlight control. Part of the company's PowerWise® energy-efficient product family, the device drives up to 11 high-current LEDs in series, meeting the needs of today's portable media devices — such as smart phones — for increased multimedia content that are fueling the trend toward larger displays and longer video playback, which require more power.

Offered in a 12-bump micro-SMD package measuring 1.615 × 1.215 × 0.425 mm, the LM3530 uses sophisticated ambient-light-sensing algorithms and content-adjustable backlighting to optimize the display, realizing up to a 55% power savings versus 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-in. 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% and 55%, 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.

The LM3530 current-mode boost converter can supply up to 29.5 mA to 11 white LEDs from a single-cell Li-ion battery. A wide degree of programmability via an I2C-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 and a separate PWM 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. Logarithmic and linear LED brightness mapping provides flicker-free dimming.

A fixed-frequency, 500 kHz boost converter provides high efficiency over the LED current range. For parallel charge pumps, the company plans to offer a product with a similar feature set. Available now, the white LED driver is priced at $1.99 in 1,000-unit quantities.
National Semiconductor
Santa Clara, CA


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