How to design analog dimming interface for external PWM for LITIX Power devices?
A microcontroller can control the SET pin by using a PWM signal filtered out with a low pass filter:
The PWM signal can be mathematically decomposed as a DC signal plus AC harmonics. The harmonics are at multiple frequencies of the PWM fundamental frequency. The purpose of the low pass filter is to reduce the amplitude of the unwanted AC harmonics of the spectrum.
The cut off frequency of the RC filter has to be high enough to ensure the desired bandwidth of regulation (according to the bandwidth of the system): The PWM frequency has to be higher than the bandwidth system (10 times or more) to make negligible the effect of the residual AC spectrum components