White LED Driver
The LM3530 white LED driver from National Semiconductor Corp. is said to be the industry's smallest to offer dynamic display backlight control. Part of the company's PowerWise® family, the device drives up to 11 high-current LEDs in series, illuminating larger displays in portable media devices such as smart phones.
Offered in a 12-bump micro-SMD package measuring 1.615 × 1.215 × 0.425 mm, the LM3530 uses ambient-light-sensing algorithms and content-adjustable backlighting to optimize the display, realizing up to a 55% power savings compared to 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 downloadable multimedia 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 darker picture in the movie trailer garnered further power savings because the backlight was reduced more frequently for dark images.
The current-mode boost converter can supply up to 29.5 mA to 11 white LEDs from a single-cell Li-Ion battery. Programmability via an I2C-compatible interface enables the designer to adjust for lighting effects such as fading, external ambient conditions, lighting level, and brightness.
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. Available now, the white LED driver is priced at $1.99 in 1,000-unit quantities.
Santa Clara, CA