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DRV8825: Large audio noise with 3 drivers enabled`

Jack Wells
Prodigy 30 points
Part Number: DRV8825
Other Parts Discussed in Thread: DRV8886, DRV8886AT

Hi,

I have designed a pcb with 3 DRV8825s to drive 3 different axis. All drivers have the following settings:

Voltage: 24v

Current resistor - 0.1ohm

Current setting - 1.6A (can not be changed by uC)

Microstepping: 1/16

Decay: Mixed (can not be changed by uC)

The PCB is 2 layers.

The motors have the following stats:

The issue is when all 3 motors are energised. Working with 1 motor there is no audioable noise that is noticeable. 2 Motors there is a slight "buzzing" sound coming from the 2 motors and when a 3rd motor is run then there is a lot of noise - humming, buzzing, hissing. It sounds like the white noise of an old TV channel. This only occurs when the motors are stationary. It also feels like the motors are vibrating slightly. What can we do to fix this issue? Any recommendations for removing this noise. And is it damaging to the motors?

Thanks,

Jack

Schematics attached:Scotsat Main PCB V3 Schematics.Zip

  • 0
    TI__Guru** 114905 points
    Hi Jack,

    We will investigate and reply soon.
  • 0 in reply to Rick Duncan
    TI__Guru** 114905 points
    Hi Jack,

    First, this noise should not be damaging to the motor.

    There are a few things to try, although your schematic shows it may be difficult.

    1) Once the motors are stationary, please change the VREF voltage. In many cases, the current can be lowered while holding. If this reduces or eliminates the noise, you can add the ability to adjust the current when holding.

    2) Change to fast decay. This looks like a more difficult option based on the layout.

    If you find that reducing the current when holding helps and your current requirements are less than 2A, please consider using one of our later stepper motor drivers such as the DRV8886 or DRV8886AT. Both of these reduce the number of components required (no sense resistors) and have a TRQ pin that can change the current to 100%, 75%, and 50%.

    If interested, the following thread may be of benefit: e2e.ti.com/.../2197343
  • 0 in reply to Rick Duncan
    Prodigy 30 points
    Hi Rick,

    Thanks for taking the time to look into this. I will upload a brief video so you can appreciate the noise we're hearing.
    goo.gl/.../omi89chh4nM36x6n7

    We can not lower the current any further or the motors will not have enough torque,

    Again, when individually run the motors are near silent and no audio issues are present.

    I believe there are certain draw backs to using fast decay mode. Can you describe the difference?

    Thanks,
    Jack
  • 0 in reply to Jack Wells
    TI__Guru** 114905 points
    Hi Jack,

    Sorry, I may not have been clear. I was proposing lower the torque to evaluate the effects when holding. You would move the motors with the normal torque. Once the motors are stopped, the pots would be adjusted for lower holding torque to determine if this method could help.

    Depending on the system, motors can have different torque requirements for movement versus holding.


    Fast decay has more current ripple (less torque) than mixed decay.
  • 0 in reply to Rick Duncan
    Prodigy 30 points
    Hi Rick,

    Sorry my mistake. Should have set the motors to a hold position. New vid - goo.gl/.../mtEkepMRubK2pMqi8

    Again, when there is only 1 or 2 motors the noise is very much reduced. Is there a reason that multiple drivers on the same board would directly effect each other? We have a large 4700uf capacitor in place to reduce any voltage spikes.

    I saw from the related post you mentioned that the sense resistors require a good path to ground. I've tried to implament this with wiring on the board but it made no difference. Also reducing the current only has a marginal effect to the noise.

    I will attempt to try with the motors in a fast decay setting.

    Any other advice would be greatly appreciated,

    Jack