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Spike noise on current feedback terminal

Junji Takiguchi
Prodigy 250 points

Good day everyone.

Now we are trying to improve our motor performance with DRV8312-69M-KIT.

On that process, we found that there is high level spike noise on current monitor terminals. (OP amp output IA-FB, IB-FB and IC-FB)

It seems that it synchronous to PWM switching. (Please see attached file.)

In my understanding, current value sampling execute at the timing PWMA=PWMB=PWMC=Low.

So I think attached waveform is acceptable because there is no noise during this period...

Is it correct?

 

And as another concern, I worry this noise will give a bad effect for dynamic performance due to not correct current feedback when motor accelerate or deceleration.

 

Is my understanding about current sampling timing?

Does it necessary to reduce this spike noise? Or is it acceptable?

Please advice

 

Thanks.

J Takiguchi

 

J Takiguchi2308.Waveform.pdf

  • 0
    TI__Guru** 119680 points

    You are sampling the currents through the low side shunt starting at the middle of the high-side PWM off-period. The spikes are occuring at the switching point, so in general they will not be effected.  But, as the duty cycles for a phase get very large this switching noise may get picked up on another phase which is sampling, this is what makes the areas in the over-modulation region so challenging.  The soltuion in proj_lab10 works well for many motors, but we have made some improvements and will eventually release an enhanced version of the modulation that does an even better job of getting clean current signals.

    just as important is good symmetrical layout with a kelvin ground connection.