austriamicrosystems (Unterpremstaetten, Austria) has released the AS3674 and AS3490 LED backlight drivers for smartphone LCD displays. The LED drivers enable application efficiency at a peak level of 90%, including the DC/DC converter and the current sources. The drivers, which feature a PCB footprint of 11.5 mm², require just four external components.

The AS3674 is a 2-MHz DC/DC switch mode step-up converter controlling 5 current sources. The current for the LED channels can be set by an external resistor with a maximum of 25mA 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 easily integrated into noisesensitive 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.

The AS3674 operates from a 2.5 to 5.5V 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 a 12- ball WL-CSP package (1.7 × 1.4 x 0.5 mm, 0.4 mm pitch).

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