Semtech Corp., a supplier of analog and mixed-signal semiconductors, announced the SC652 and SC656 LED backlight charge pump drivers. As new members of the SC65x tiny charge pump platform, these devices are the industry’s first LED drivers to integrate digital low-pass filters that convert a PWM dimming signal’s duty-cycle into DC current for LCD backlighting with white LEDs.

Both parts are optimized for single-cell Li-ion battery handheld applications. The SC652 supports up to five LEDs with one PWM dimming input. The SC656 supports up to seven LEDs with one or two independent PWM dimming inputs for end products that have multiple zones of lighting.

Recently, PWM dimming has become more popular due to its flexibility, cross-platform firmware compatibility, and extensive use in advanced power saving schemes such as ambient light sensing (ALS) and content adaptive brightness control (CABC). However, most competing PWM dimming solutions simply turn on and off the LED current in synchronization to the PWM signal, resulting in three distinct negative effects: 1) increased voltage ripple on the input and outputs of the LED driver, which can couple noise into nearby circuits, 2) decreased efficiency because the LED forward voltage remains high even when dimming, and 3) potential display flicker, banding, or herringbone pattern noise due to the LED light interfering with the LCD refresh rate.

The SC652 and SC656 are the first devices to fully solve the above issues without the addition of any external components, the company claimed. Semtech’s proprietary digital low-pass filter samples the PWM dimming signal to extract the duty cycle information and maps this into the current setting DACs. The PWM input accepts 200Hz to 50kHz PWM signals with logic level of 1.4V and above. LED current is linearly proportional to duty-cycle from 1% to 100%, while 0% duty-cycle places the IC into 0.1uA shutdown. Under all conditions, LED current remains DC to minimize input/output ripple, reduce LED forward voltage to allow the 1x/1.5x/2x charge pump to operate in the most efficient mode possible, and to eliminate any possibility of interference with the LCD refresh rate. In addition to these critical benefits, the PWM dimming filter inherently responds to sudden changes in duty-cycle with an aesthetically pleasing automatic fade up/down in LED brightness to add a high-quality feel to the end product without needing any special software subroutines in the host system processor.

The SC652 is available in 2x2mm lead-free 14-pin MLPQ-UT package. The SC656 is available in 3x3mm lead-free 20-pin MLPQ-UT package. Both devices are halogen-free and comply with the European Union's Restriction on Hazardous Substances in Electrical and Electronic Equipment (RoHS) directive to meet worldwide environmental and regulatory requirements.