Smartphone LCD backlight LED drivers offer industry's highest efficiency and smallest PCB area

February 27, 2012 // By Christoph Hammerschmidt
Austriamicrosystems announced the AS3674 and AS3490 LED backlight drivers for smartphone LCD displays. These new LED drivers enable the industry's best application efficiency at a peak level of 90%, including the DC-DC converter and the current sources. With a PCB footprint of only 11.5 mm², and just four external components required, the AS3674 and AS3940 are well suited for smartphones and other mobile devices where space is at a premium.

The AS3674 backlight driver family complements austriamicrosystems' portfolio of lighting management units which address backlight, smart light and ALS (ambient light sensing) processing inside a single IC. The AS3674 is a highly efficient 2 MHz DC-DC switch mode step-up converter controlling 5 current sources with each driving 2 LEDs in series. For added flexibility, the current for the LED channels can be set by an external resistor with a maximum of 25 mA per channel. The AS3490 incorporates the same functionality as the AS3674 but addresses only three LED channels.

A soft startup feature allows the AS3674 to be integrated into noise sensitive RF systems. The AS3674 is controlled by two enable inputs which can also serve as PWM inputs between 100 Hz and 800 Hz with 1:2000 dimming ratio. The 2 LED per channel configuration combined with the 2 MHz operating frequency of the converter allow the use of tiny external components such as a 4.7 µH coil and results in very high efficiency, up to 6% higher than the closest competitor.

The AS3674 operates from a 2.5 to 5.5 V power supply and includes a number of safety features such as under-voltage lockout, overcurrent and over-temperature protection and LED testing. Both the AS3674 and AS3490 are housed in space saving 12-ball WL-CSP package (1.7 x 1.4 x 0.5 mm, 0.4 mm pitch).

Image1: AS3674 block diagram

For more information on the AS3674 and AS3490 please visit and