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DRV8811 / motor current waveform of mixed decay mode

K.Yaita
Guru 29720 points
Other Parts Discussed in Thread: DRV8811, DRV8818
Hi Team,
 
My customer is evaluating "DRV8811+ stepping motor(MINEBEA)" and saw the waveform attatched.
CH3:motor current
CH4:VREF
 The motor current seems to have distortion(red part).
Is there any concern about this wavefom?
I'd also like to know why this occurs.
 
The test condition is the following.
------------------------------------------
- step frequency: 8kHz
- microstep mode: eighth-step
- full scale chopping current: 0.8A
- decay mode: mixed decay mode
------------------------------------------
It is ODM project for my customer, so unfortunately he can't provide the schematic.
Your advice would be appreciated.
 
Best Regads,
Yaita / Japan disty
  • 0
    TI__Mastermind 26065 points

    Hi Yaita

    It is quite often to see this kind of current waveform when stepper's speed gets higher. The reason is because there is no enough time for the current to decay down during the latter section of current decreasing cycle.

    We can lower down the speed to very slow rate such as 5 rpm. If the current waveform is still shown like this, then we need to tune the decay parameters by increasing the fast decay time for every PWM cycle.

    This current shape has no harm to the application. Since it is happened when speed is higher, there will be little sensable vibration due to this distortion.

    Best regards,

  • 0
    TI__Mastermind 20985 points

    Yaita-san, see this Test Data from the similar DRV8818, which is from this TI Design.

    Best regards,
    RE