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DRV8801: Is it possible to measure Back-EMF tru VPROPI pin of DRV8801

can altineller
Expert 1760 points
Part Number: DRV8801


Hello,

Is it possible to measure the back-emf tru the vpropi pin on drv8801. I thought so, I have an ADC triggered exactly on the middle of pwm on and pwm off times, twice per cycle, and measured the difference. 

To my surprise, for a small motor, the measured vpropi is higher while pwm is off. I am investigating whether my interrupt handler for the ADC is doing the measurements correctly, and so I am trying to verify - if the measurements are not swapped. (Triggering ADC tru pwm module on a tiva-c  for load and zero, and then the adc isr handler checks for pwm_0 raw status, and decides whether this interrupt came while middle of 0 or high)

Either way, is it possible to measure back-emf, or vpropi is just an indicator or motor current.

Best Regards,

C.

  • 0
    TI__Mastermind 22050 points

    Hello,

    It's difficult to measure back emf of brushed-dc motor while driving. One of the easiest ways would be to try to measure voltage across motor or outputs during Hi-Z state or using a resistor divider attached to output pulled-up to VBB. 

    What's the reason for needing back-emf measurements?

    Best,

    David

  • 0 in reply to David Medis
    Expert 1760 points

    I would like to make a cascaded pid loop where the inner loop compares current with a reference created by outer loop. I managed to sample  the drv8801 vpropi output during hi-z state, but don'r really want to modify output circuit.

    is VPROPI is just an indicator of motor current, or does it have back-emf information during hi-z states of the motor?

  • +1 in reply to can altineller
    TI__Mastermind 22050 points

    Hello,

    The VIPROPI is only the voltage output that's proportional to motor winding current.

    Best,

    David