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DRV8312: EMI grounding prefer for servo shielded cable

Rez Kh
Prodigy 110 points
Part Number: DRV8312

Hello,

I don't know is a good place to ask a question about grounding servo cable shield.

My question is:

Do you prefer grounding the servo cable shield on both side ( PCB and Motor ) or one side to eliminate the ground loop. if you approve the on side grounding, prefer the motor side that connected to chassis or PCB side?

Do you also prefer the same for hall sensors cable too?

Thanks a lot.

  • 0
    TI__Genius 13630 points

    Hi Rez,

    Thank you for posting to the Motor Driver's forum!

    I will aim to provide a response by the end of the week.

    Best,

    ~Alicia

  • 0
    Prodigy 110 points

    Thank you, I believe also the ST-Curve PWM method work better than trapezoidal PWM for eliminating a share edge on motor current, Is that can be also true?

  • 0
    Genius 5040 points

    Hi Rez,

    Rez Kh said:
    Do you prefer grounding the servo cable shield on both side ( PCB and Motor ) or one side to eliminate the ground loop. if you approve the on side grounding, prefer the motor side that connected to chassis or PCB side?

    It's great question. In general we would avoid the ground loop and only ground the shield at one end. But in this case, if the motor housing is already grounded (there is induced current on the body from the changing magnetic filed from the rotor and stator) then I would only ground the cable shield at the pcb end. If the motor housing is not grounded, then I don't want to have the noisy housing floating with the EMI, and so I would ground the housing to the shield too with the other end grounded to the pcb. The induced current on the housing should be very small so any loop current is very small.

    Brian

  • 0 in reply to Rez Kh
    TI__Expert 3020 points

    Hi Rez,

    Thank you for the follow up. To confirm, by ST-Curve do you mean S-Curve control? If so, this control method will indeed produce a smoother waveform than trapezoidal control.

    Best,

    Davis

  • 0 in reply to Davis Jackson
    Prodigy 110 points

    Yes, ST-Curve control I mean.
     Thank for reply about EMI shield grounding.

  • 0 in reply to Rez Kh
    Genius 5040 points

    Hi Rez,

    Rez Kh said:
    I believe also the ST-Curve PWM method work better than trapezoidal PWM for eliminating a share edge on motor current, Is that can be also true?

    If you meant ST curve = S-curve, then it has nothing to do with pwm or not -- I'm confused. S-curve control or more correctly s-curve motion profiling is a motor controlling technique by the MCU to have smooth acceleration/deceleration and it has nothing to do with the motor 3 phase driving pwm signals. If you're talking about the pwm signal outputs of the driver driving the power FETs, then you might have the option to use trapezoidal commutation, or sinusoidal or the Saddle waveform which produces the sinusoidal voltage between the 2 phases (but it has the saddle waveform on each phase) and it has less pwm switching cycles (section of 0v in one period). The EMI from the edge of the pwm signal is the same though. 

    Brian