I am trying to understand this application note from Microchip about using PWM and a low pass filter to generate an analog output. I have a few questions regarding to the article:
In the example they use a 20kHz PWM with K = 5 so we have a 4kHz cut-off frequency. Why choose K = 5? Is it a practical rule? Or is there any reason to choose K = 5?
Then, they calculate R and C, I understand that, but after that they calculate how many dB the 20kHz signal from the PWM is cut-off (I don't really understand what they mean) and they get -14dB but according to my math I get -10.43dB with:
- F = 20kHz
- R = 4K
- C = 0.01uF