I just had a quick glance at the PWM documentation but I don't fully grasp it anyway: I select one of the 16 internal PWM controllers, set it's clock/frequency

I just had a quick glance at the PWM documentation but I don't fully grasp it anyway: I select one of the 16 internal PWM controllers, set it's clock/frequency and then bind an output pin to that. I thought that fading a LED would then stick to the frequency of the PWM controllers, but it seems I still have to take care of the speed? I thought setting the PWM frequency to 100 Hz and cycling my LED brightness from 1 to 100 would take 1 second. It doesn't work that way it seems?!?