• State Resolved
  • Locked Locked
  • Replies 4 replies
  • Subscribers 29 subscribers
  • Views 384 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

DRV10987: over current fault during open loop start

David Gustavson1
Prodigy 140 points
Part Number: DRV10987

Hi,

I am getting an over current fault (reg 0x00, bit 11) during start up.  It is Vcc dependent.  If Vcc is 8V, the motor will run OK.  If I increase above that, the motor will spin for a few seconds and stop, and keep retrying every 5 seconds.  I need the motor to operate with a Vcc of 22V.  I have the open loop current set to 0.4A and transition to closed loop operation disabled.  I don't have a current probe for my scope, so I don't know what the actual current is.  I can only measure the current in the ground leg to the power supply using a 0.1 ohm resistor.  That current peaks at about 0.5A.

I am wondering if the motor winding has too little inductance.  Are there ever situations when you need to add fixed inductors in series with each motor phase?

Thanks,

Dave Gustavson

  • 0
    TI__Mastermind 24405 points

    Hi David,

    Thanks for posting your question in MD forum. The device triggers Overcurrent fault in the event of a short-circuit condition on the motor phases. This includes phase shorts to GND, phase shorts to phase, or phase shorts to Vcc. This fault gets triggered because the current drawn by the motor phases is above 4.25A. The reason why you do not see this fault at low voltage might be because at low voltage, the current drawn might be less than 4.25A. Can you check if there is a any short across phase-GND, phase-phase or phase-Vcc? Are you using a custom board or the DRV10987EVM? What is the motor coil resistance and inductance?  We add inductors to eliminate noise and current ripples but I don't think this can help in solving this issue. 

    Regards,

    Vishnu

  • 0 in reply to Vishnu Balaraj
    Prodigy 140 points

    Hi Vishnu,

    Thanks for your reply.  I measured phase to phase with a multimeter and they all measure ~1.9 ohms.  Phases to GND or VCC are all >100K.

    I measured the winding inductance, and it is ~180uH, so the current ripple shouldn't be that bad. 

    This is my own board design.

    How sensitive is this over current protection?  Can it be noise triggered? How long does the current have to be over 4A?  <200ns?  Can it be triggered if the deadtime is too short?

  • 0 in reply to David Gustavson1
    TI__Mastermind 24405 points

    Hi David,

    Even I think this could be noise triggered. Overcurrent protection in DRV10987 is very sensitive. Yes, dead time can cause a shoot through! What is the dead time set to? The recommend minimum dead time is 440 ns for 24-V VCC and 360 ns for 12-V VCC. Also, did you make sure all the external components are TI recommended parts? See table 36 in datasheet for the list of external components. Also,can you make sure your schematic and layout is consistent with the DRV10987EVM Hardware design files? Click here to download the hardware design files. 

    Regards,

    Vishnu  

  • 0 in reply to Vishnu Balaraj
    Prodigy 140 points

    Hi Vishnu,

    Thanks, changing the dead time to 440ns made the over current fault go away.

    Dave Gustavson