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DRV8825 EMI

JULIA TRUCHSESS
Intellectual 300 points
Other Parts Discussed in Thread: DRV8825

The current-chopping scheme of the DRV8825 - rapidly switching large currents at more or less random intervals - seems like one of the best possible ways to generate broadband RF noise, and I'm surprised not to find anything in the datasheet about EMI control. I believe I'm going to need to limit the rise and fall times of the motor winding pulses in my application - anyone have any experience with this or suggestions? I think it will have to be via L-C filters but I will need to avoid resonances.

Also, is grounding of the motor housing significant?

Thanks in advance,

Julia

  • 0
    TI__Mastermind 26065 points

    Hi Julia

    L and C on the outputs should be help with the EMI control. 

    In LC method, If C (to ground) is to be used, we should make sure that proper L(in serial) is also presented to avoid OCP issue caused by the charging current to the capacitor.

    Also ferrite bead may be help. The following post can be your reference.

    http://e2e.ti.com/support/applications/motor_drivers/f/38/p/284878/993894.aspx#993894

    Best regards,

  • 0 in reply to Wilson Zuo
    Intellectual 300 points

    Thanks, Wilson, those other threads are very informative. What do you think about an L-C filter on the VM supply to the driver IC? I have seen this technique recommended by other driver manufacturers.

    Julia

  • 0 in reply to JULIA TRUCHSESS
    TI__Mastermind 20985 points

    Julia, an LC on the supply will filter high frequency noise coming in.  Noise on the supply can also be passed to the output.  The need for it depends on how much VM noise you have to begin with.

    Best regards,
    RE

  • 0 in reply to RE
    Intellectual 300 points

    Actually, my impression of the LC filter on VM is not that it is to prevent system noise from getting into VM, but to limit the maximum rate of change of the current into VM, i.e. it's a way of reducing the current slew rate on (and hence EMI from) all of the motor outputs at once using only one filter instead of filtering each motor output individually. Does that sound plausible?

  • 0 in reply to JULIA TRUCHSESS
    TI__Mastermind 20985 points

    Hi Julia,

    If the C is placed next to the VM device pin, and L goes to the power plane, it's a low-pass filter for what I was talking about.

    What you're saying would involve placing the L next to the device pin, and C on the power plane.  The problem with using this technique to limit current is that VM at the device pin will drop in voltage when there's a surge of current.  VM for the DRV device needs to be stable, or else UVLO might trip, or the device might misfunction if VM drops below the spec range.

    Best regards,
    RE