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DRV8711: Issue with one of the phases of DRV8711 output

Galen Church
Prodigy 170 points
Part Number: DRV8711

I was experiencing some weird harmonic noise with the steppers being driven by my new DRV8711 circuit.  When scoping the current wave-forms it is clear that there is an issue with one of the phases that ends up causing a resonant wobble in our mechanical armature.  Does anyone know what could be causing this?  I have reproduced similar results with all of our prototype boards which leaves me to believe it is a design/configuration issue. I am configuring the drivers as follows: 0x0C41, 0x1145, 0x2030, 0x31FF, 0x4510, 0x6055 (I am leaving STALL as default for now).

Phase A (BAD):

Phase B (OK):

The issue becomes more noticeable at higher uStepping resolutions.  This is 1/256, Phase A again:

Any help/hints/guesses would be much appreciated.

Thanks,

Galen

  • 0
    TI__Guru** 114905 points
    Hi Galen,

    We will investigate and get back to you. It may be mid next week before we can respond. Sorry for the delay.
  • 0 in reply to Rick Duncan
    Prodigy 170 points
    OK, thanks. Let me know if you need some more information.
  • 0 in reply to Galen Church
    TI__Guru** 114905 points
    Hi Galen,

    I have a few recommendations.
    1) Assuming I have read the registers correctly, the TDECAY setting is longer than the TOFF setting. This should be reversed. Please try setting register 0x04 to 0x124 (18us fast decay, 6 us slow decay).
    2) At the higher levels of microstepping, please set the ABT to 1. This will help regulate better below 30% of full scale current.

    From the datasheet:
    For higher degrees of micro-stepping, TI recommends enabling ABT bit for better current regulation.
  • 0 in reply to Rick Duncan
    Prodigy 170 points

    Hi Rick,

    Thanks for the response.  Those suggestions were very helpful.  Following those guidelines I have been able to dial-in the TDECAY and TOFF Settings to get a pretty decent waveform on both phases.  Right now I have 0x4 at 0x0104 (2uS) and I increased the spread on the TOFF to 0x55 (42.5uS).  I also brought TBLANK down to 0x55 (2.7uS) and enabled ABT, i.e. 0x3 = 0x0155.  This has given me pretty good results (workable) when running at 1/128 uStepping.  There is still a noticeable "hiccup" just before zero-crossings on the waveform though.  My control function implements an acceleration profile and the hiccup is almost non-existent at speed (Steady-State) but much more noticeable at the slower speeds in acceleration and deceleration. attached are some plots for reference:

    Phase A at speed (1/128 uStepping):

    Phase B at speed (1/128 uStepping):

    Phase A in deceleration (1/128uStepping):

    Phase B in deceleration (1/128 uStepping):

    If I increase uStepping to 1/256 the issue is again amplified.  Phase A in deceleration (1/256 uStepping):

  • 0 in reply to Galen Church
    Prodigy 170 points

    Just as a reference to anyone else.  I was able to clean this up more by taking a look at the circuit layout.  I realized the current sense circuit for B (the better channel) had a much cleaner route from R_SESN_B to the pins BISENP and BISENN, then R_SENS_A and AISENP and AISENN did.  Specifically, the return path AISENN was using relying on the ground plane rather then its own trace for a large section.  Cutting that and jumping around it with a discrete wire straight from the sens resistor to the pin has given me a much cleaner wave-form.  ...hopefully a PCB Rev will clean it up even more.

  • 0 in reply to Galen Church
    TI__Guru** 114905 points
    Hi Galen,

    Thank you for following up with this information. I hope others can benefit by your findings.