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DRV8711 "Noisy" winding current

Blazra
Prodigy 20 points
Other Parts Discussed in Thread: DRV8711, DRV8711EVM

Hello,

we have motor driver with DRV8711 on custom PCB. In full step it's working quite OK, but with higher microstepping levels it's unable to drive the motor. Winding current looks different than waveforms in the datasheet or app notes. It's changing with different configurations, but the spikes are always there, they just get larger with higher voltage. Measured on 0.47R sense resistor with 12V supply voltage. Can someone please tell us what are we missing?

Thanks.

Scope screenshots: 

  • 0
    TI__Guru** 114905 points
    Hi,

    Can you provide some additional information?
    What is the step rate at full step when the motor is running OK?
    What microstep rate is used when the motor is not running OK?
    Does the motor run at all when microstepping?
    What are the motor specifications (R / L / voltage or current rating)?
    What are the settings used? Can you provide screenshots?
    Have you tried using automixed decay?

    By the way, the winding currents shown is using a current probe. This allows the current to be monitored by clamping around a wire, and shows both directions.
  • 0 in reply to Rick Duncan
    Prodigy 20 points
    I don't have a current probe, but I connected external sensing resistor 0.47R in series with motor winding - I am not using sense resistor for DRV8711 - that is 0.01R.
    I have tried step rate from few Hz to 100 Hz and it's running OK , I didn't tested higher yet. For microstepping I tried various step rates in that range with no luck.
    In half step it turns, but in 1/4 step it's starting to loose steps - in 1/8 and others it's just shaking or loosing many steps.
    The motor parameters are: 0.32R 1.45mH 6.6A all per phase.
    Settings:
    0x140 TORQUE
    0x010 OFF
    0x101 BLANK
    0x510 DECAY
    0x310 STALL
    0x00F DRIVE
    0xF01 CTRL

    I have tried automixed decay and it didn't help - I have tried probably every register option there is... Screenshots of what would you like?

    Thanks for help.
  • 0 in reply to Blazra
    TI__Guru** 114905 points
    The screenshots were the register settings. They are available via the DRV8711EVM. I did not see anything in the settings that looked like it would cause the DRV8711 to malfunction.

    When changing from full step to microstep, do you start stepping at a rate equivalent to the same number of full steps per second? If full step is working at 100 Hz and changing to 1/2 step, suggest you try a step rate of 200Hz. This is effectively the same speed as full step.

    I have not experienced resonance, but it typically appears between 70 and 120 steps per second at full step. Can you provide more details on full step and half step? A table of working step rates at each step mode may help narrow the problem.