• State
  • Locked Locked
  • Replies 5 replies
  • Subscribers 30 subscribers
  • Views 800 views
  • Users 0 members are here
Support feedback
Options
Options
Related

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.

DRV8711 holding and motor vibrates

Austen Chan
Prodigy 30 points
Other Parts Discussed in Thread: DRV8711

Hi,

I have a design with DRV8711 to drive and hold 2 step motors. The circuitries and motor are identical. The parameters are set to be the same. However, one motor would vibrate while holding when the other one wouldn't. If I drive the motor to move 1/2 step, it would turn quite. Another 1/2 step would bring the vibration back. The motor on the other stays quite regardless how many steps I drive it. I've tried using motor from a different batch and the result is the same. The layout on the board for both drivers are pretty much identical, so the layout doesn't seem to have any cause to this problem. Is there any thought about this?

Thank you

  • 0
    TI__Mastermind 21320 points

    Hi Austen,

    Can you verify this on multiple PCBs? This sounds like one of the H-bridges has a soldering issue or open. Can you check the voltage/current waveforms for each H-bridge? Can you also share your schematic?

  • 0 in reply to Nicholas Oborny
    Prodigy 30 points

    Hi Nick,

    This behaviour happened on all PCBs we have. The PCBs were machine built, so the soldering issue should be minimal or none. I also checked the soldering on the boards, they were nicely done. I managed to eliminate the vibration by removing the optional filter on R_ISENSE.

    The driving circuit of my design was the same as on page 16 of the datasheet. The FET I used was IRF7341, R_ISENSE was 51mR, optional filter was 100R and 560pF. The vibration went away by removing the 560pF and replaced 100R with 0R. I try to understand why would this filter create such an impact to control.

    When I measure the voltage and current waveform on the problematic driver side , I found the duty cycle on the motor was not fix and the current had some random frequency ripple during holding. It looked to me that the driver was constantly trying to compensate and regulate.  I drew the waveform out as the screen capture doesn't really show how it was.

    Thanks,

    Austen

  • 0 in reply to Austen Chan
    TI__Mastermind 21320 points

    Austen,

    The DRV8711 will employ current regulation to maintain the position of the stepper motor. The current regulation methods and how the level is determined are outlined in datasheet. An RC filter on the SENSE line could affect the accuracy of the readings from the internal amplifier. I would suggest removing this.

    Is there any particular reason you have an RC filter on the SENSE line?

  • 0 in reply to Nicholas Oborny
    TI__Mastermind 21320 points

    Austen,

    Sorry, I see that we do have an option for an RC filter. Can you confirm the values and tolerances for the filter. Do you have an R on both the SENP and SENN?

  • 0 in reply to Nicholas Oborny
    Prodigy 30 points
    Hi Nick,

    The resistors are 1% and on both SENP and SENN pins. The capacitor was 5%.

    Thanks,
    Austen