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TIDA-00961: How phase shift is actually implemented

Dmitry Sharihin
Intellectual 420 points
Part Number: TIDA-00961
Other Parts Discussed in Thread: TMS320F280049, TIDM-1001

Hello,

I'm trying to implement something similar to TIDA-00961 design.

I've read control code for TMS320F280049, however it is a bit difficult to understand (lot of global variables without clear definition, spaghetti code for ISR etc).

So, here's the question: can someone explain how to implement correct phase shift for two EPWM modules in up-count mode with variable frequency without high resolution period?

What steps I should actually do in PWM and control ISR?

What maximum ISR rate ratio could be implemented (e.g. can I change period every switching cycle or I should wait at least 2/3 PWM cycles)?

Thanks

  • 0
    TI__Genius 10820 points

    Hi Dmitry,

    TIDA-961 may not be the best reference for this as it has a lot of time-critical code inside the ISR. TIDM-1001 could be a good reference if you want a fixed 180 degree phase shift between two PWM modules in up-down count mode. For up-count mode please see my post below for reference:

     

    Note that the global and one-shot register reload mechanism on type-4 PWMs (available on F28004x devices) further simplify this implementation. I hope this helps.

    Hrishi