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EPwm compare value

mosin
Expert 1160 points

Hi,

I have an UP/DOWN Pwm that I change duty cycle for control. I was wondering if there was any problems setting a compare value equal to PRD or to zero to "force" a state, On or Off. I would like to avoid sofware force this way if it's possible. 

DSP used : F28377S

Thanks!

  • 0
    Guru 192875 points

    Hi Mosin,

    I was wondering if there was any problems setting a compare value equal to PRD or to zero to "force" a state, On or Off. I would like to avoid sofware force this way if it's possible.

    Yes, you might observe malfunctioning of the module. I've observed the same esp. when CMPA value equals 0. Please go through this extract and assign CMPx=1 and CMPx= TBPRD-1 for minimum and maximum duties.

    Regards,

    Gautam

  • 0 in reply to Gautam Iyer
    Expert 1160 points

    Hi,

    thanks for pointing me this paragraph. I understand that that a very short pulse could not be problematic but I'm trying to avoid it... Anyway, I have dead times greater than 1 cycle so , if I set CMP  to PRD-1 or ZERO+1, it would be lost in the dead times. Would that still be safe?

    Thanks

  • 0 in reply to mosin
    Guru 192875 points
    Anyway, I have dead times greater than 1 cycle so , if I set CMP to PRD-1 or ZERO+1, it would be lost in the dead times. Would that still be safe?

    I didn't understand the above statement, can be a bit more clearer?

    Regards,
    Gautam
  • 0 in reply to Gautam Iyer
    Expert 1160 points
    The dead times that we have are around 500ns. If I set the compare value to 1 or TBPRD-1, the resulting pulse wouldn't be visible because it would be smaller than the dead times. This would result in no pulse at all. My question is, would that still be a viable option.
  • 0 in reply to mosin
    Guru 192875 points
    This would result in no pulse at all.

    This would be a tricky situation right? You'll need to apply your saturation limits like 50 to 400 for a TBPRD of 450 etc.

    Regards,
    Gautam
  • 0 in reply to Gautam Iyer
    Expert 1160 points

    Hi Gautam,

    That's what I'm looking for :)  I need to set some PWM to 1 or 0 at certain point. I was using software force before but I'm trying to streamline everything to use CMP values.

    Best regards,

  • 0 in reply to mosin
    Guru 192875 points
    Great!

    Goodluck & Regards,
    Gautam