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TMS320F28031 - COMPARATOR trip event error

Marc-olivier Brassard
Prodigy 70 points

Hi everybody,

I have an issue with the behaviour of the digital comparator event 2 cycle by cycle tripping event. In our system, we use this comparator to stop CBC a PWM when the value configured into the DAC his reach.

I made multiple trial without any issue, but when I reach a particular open time of my PWM the PWM trip zone CBC seems to discard my comparator output value.

I took the picture below to help understanding my issues

 

CH1:    Gate right top

CH2:    Gate left top

CH3:    Comparator 2 output signal

CH4:    Comparator 2 non inverting input signal

As I observe on the fourth event on the channel 4, the comparator output signal is force to 1 when the comparator non inverting input has reach my set value, but I observe no effect on the corresponding PWM (CH1). That error generate an instability in our system.

I validate all configuration and for this moment they seems to be okay, but if you need more detail about the software configuration, just ask me!

Any body can help me with this particular issue??

Marc-Olivier Brassard, Jr. Eng.

Electronic designer 

  • 0
    TI__Guru 61235 points

    Marc-Olivier,

    Are you able to check the TZFLG register when the problem occurs?  It would be good to know what the DCxEVTy and CBC bits show, assuming you are clearing it after each correct event (you may not be clearing it).

    I'm wondering if your two event count get messed up by noise on the comparator output, causing the trip to occur where you don't want it,  Maybe, maybe not.  Just examining the possibility.

     

    Do you have a spare ePWM module that you can test with?  If so, you can setup that ePWM module for some constant duty cycle, and have it trip on EVERY event from the same digital compare as above.  If we see this spare ePWM trip but your original (two event configured trip) ePWM does not trip, then it suggests the trip event counter got confused.

    - David

  • 0 in reply to David M. Alter
    TI__Guru 61235 points

    Closing out this thread.  The poster advised offline that they had mistakenly setup the blanking window width to a value of 505.  The blanking window width is only an 8-bit value, so max value is 255.  They have adjusted their blanking configuration, and things are working correctly now.

    - David