Hi all,
Does anyone have any general thoughts as to applying some spread-spectrum modulation of the base PWM frequency?
I would think that for most applications adding jitter to the system clock (and thereby the PWM subsystem) is not really an option, as this would also affect various communications interfaces (UART, CAN, and so on), which are somewhat sensitive to the amount of clock jitter that would be useful for spread-spectrum modulation (IE. variations of several percent).
I was instead thinking about altering the PWM period registers on-the-fly, during runtime. However, maintaining synchronization between them as well as the compare registers seems non-trivial, and may even unachievable (?). The heart of the issue seems to be, to me, that the difference in duty cycle between the channels is really what controls the current per motor phase, making it necessary to change all the period and compare registers simultaneously, and in some cases the count direction as well. Ensuring that this can be done and applied within one PWM base clock makes things even more difficult.
Is there anyone here that's thought through this more than I and has an idea of how to do this? (Or alternately, if someone's deduced that spread-spectrum modulation isn't really achievable short of adding master clock jitter).
Cheers!