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DRV8308: behavior when switching position while moving

Hong Sun
Intellectual 300 points

Part Number: DRV8308

Hello there,

I have a DRV8308 EVM which has the rev. a chip and its document stated the behavior when switching the direction while motor is moving:

"If the commanded direction is changed while the motor is moving, the device either brakes or allows the motor to
coast, depending on the state of the BRKMODE bit, until the motor stops. The stopped condition is determined
by measuring the period of the HALL_U signal; when the period exceeds 160 ms, typical operation resumes and
the motor starts spinning in the commanded direction. This prevents excessive current flow in the output stage if
the motor is reversed while running at speed."

The rev b version has only "If the commanded direction is changed while the motor is still spinning, this may cause excessive current flow in
the output stage."

in EVM board, my motor can rotate properly when I change direction by either giving a pwm duty cylce of 20% and flip the DIR  from the GUI provided by TI or stopping motor by set pwm duty cycle to 0, then 20% and then click DIR.

Now with my own development board, which has rev b. chip.   Motor might stuck which switching direction using the either one of the approach I chosen above.  if I helps the motor to move a little bit, then motor would start to rotate.   I don't know what is the problem and am wondering what is the behavior when DIR signal is toggled high to low or low to high: does DRV8308 simply reverse the commutation sequence based on the directional signal directly no matter if motor is rotated or not.  One more behavior is that when motor stuck, the LOCK signal is still set.

thanks,

Hong

  • 0
    TI__Guru 56650 points

    Hong，

    According to your description, the EVM worked fine. But, you got a trouble on your board. Would you swap the DRV8308 IC between EVM and your board since the Rev b chip was one of the concerns.

    Also, would you help list what do the changes or modifications between your board and the EVM?

    I will consult other engineers to see if they have seen similar issue before on next Monday.

  • 0 in reply to Wang5577
    TI__Guru 56650 points
    Hong,

    DRV8308 had some changes from Rev A to Rev B which may cause the Motor stuck. We had a workaround to deal with it.
    But, before we work on the Rev B control method, would you read out all the IC top marking letters on your board and EVM?
  • 0 in reply to Wang5577
    Intellectual 300 points
    On your previous question: we pretty much copy the EVM circuit except we control the DRV8308 through FPGA instead of microController as in EVM.
    on chip letter: EVM: DRV8308 TI431C A9PL G4
    my board: DRV8308 TI 831C ARKG G4

    please let us know the workaround and reference on that : we have troubleshot it for quite some time now and really run out of ideas.

    thanks,

    Hong
  • 0 in reply to Hong Sun
    TI__Guru 56650 points

    Hong,

    Thank you for your input. Would you send me a private message? So, we can discuss it.

  • 0 in reply to Wang5577
    Intellectual 300 points
    Hello Wang,
    I am confused : what do you mean "would you send me an email?". first I don't have your email address. Secondly I don't know what you are expecting me to send. Please guide me on it. And I am really looking forward to the workaround of switching motor direction.

    thank,

    Hong
  • 0 in reply to Hong Sun
    TI__Guru 56650 points
    Hong,

    When you put cursor on my name, you could see "send a private message" option. Click that, you can send me message. (You are right, not go through email. So, I updated the previous post to use e2e message.)