LED driver reduces power consumption up to 55 percent

Aug. 20, 2009
Industry’s Smallest Boost Converter Enables Better Picture Contrast, Longer Video Playback in Portable Displays

Now available is the industry’s smallest white light-emitting diode (LED) driver with dynamic display backlight control. The LM3530, a member of National Semiconductor’s PowerWise energy-efficient product family, drives up to 11 high-current LEDs in series, illuminating larger displays in portable media devices such as smartphones. The LM3530 is offered in a 12-bump micro SMD package measuring just 1.615 mm × 1.215 mm × 0.425 mm.

Today’s 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 sophisticated 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” 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.

Technical Features The LM3530 current-mode boost converter can supply up to 29.5 mA of power to 11 white LEDs from a single-cell Lithium-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 backlight LED driver can intelligently determine lighting requirements and select between various dimming options via its programmable ambient light response and separate pulse-width modulation (PWM) dimming input, thereby 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. For more information or to order samples and an evaluation board, visit http://www.national.com/pf/LM/LM3530.html.

Availability and Pricing Available now, the LM3530 is priced at $1.99 in 1,000-unit quantities. More information about National’s LED drivers is available at http://www.national.com/analog/led.

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