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TMS320F280049: CMPSS and trip zorn debug - unwanted trip happens

Sheldon He
Expert 8585 points
Part Number: TMS320F280049

Hi expert,

My customer is using CMPSS and DC/TZ module of EPWM to designing their digital power application. They hope to trip PWM output to low when CMPSS output hgih. 

The issue they met is sometimes this function can go wrong. As shown below, when CMPSS output is released, PWM is still in low state without recovery from low state which is unwanted. 

I hope to monitor some register values in control loop and give them outputed with a DAC, but I am not sure which register sets are good to watch here. Could you give me any ideas here?

Thanks

Sheldon

Green line channel is EPWM output B

Blue line is CMPSS output signal (though XBAR for debugging purpose)

  • 0
    TI__Guru 52040 points

    Sheldon,

    1. If the user wants the EPWM module to enter normal operation immediately after the TRIP signal is cleared, they must use the DC module and no the TZ module (oneshot or CBC).

    2. If using TZ (oneshot or CBC) it could be that the EPWM module has not finished a cycle or the SW hasnt cleared the oneshot.

    3. It could also be that EPWM signal is SUPPOSED to be low at that time when the TRIP is released due to the setting of CMPA,CMPB,ZERO and PRD actions.

    Nima

  • 0 in reply to Nima Eskandari
    TI__Expert 8585 points

    Hi Nima,

    [Nima] 1. If the user wants the EPWM module to enter normal operation immediately after the TRIP signal is cleared, they must use the DC module and no the TZ module (oneshot or CBC).

    [Sheldon] Since they are using CMPSS to trip EPWM, I think it need to envolve multiple modules or sub-modules here. As shown below, DC can't trip EPWM without TZ, is my understanding right here?

    BTW, a little bit confusing at the blocks below. DCAEVT2 signal has two interface in this blocks (highlighted). Does that mean this event can trip EPWM without configuring TZSEL?

    Thanks

    Sheldon

  • 0 in reply to Sheldon He
    TI__Guru 52040 points

    Correct, that was my comment about "use DC module NOT TZ oneshot or CBC". USE THE FIRST HIGHLIGHTED signal.

    Use the action in the registers for the first highlighted item. MAKE SURE THE TZSEL for CBC and the CBC logic in general is not enabled and the actions for them doesn't take place. 

    The RAW DC signal, not the one going through CBC or OST should be used if you want the EPWM to recover immediately after the DC signal is removed.

    Nima