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DRV8701: spikes on SO pin

Fabrizio Frigeni
Prodigy 50 points
Part Number: DRV8701

Hello,

I use the SO pin as a feedback to regulate and limit the motor's current. However, I observe massive spikes on the SO output voltage that make current regulation impossible. I am pasting the scope screenshot below.

I observed the following:

1. The current spikes timing corresponds exactly to the PWM voltage switching at the motor's pins. 

2. The spikes are slightly reduced, but not removed, when a lower gate current is used.

3. The spikes are essentially unchanged when disconnecting the motor. 

My question is: what can I do to remove this nasty noise besides filtering the SO readings on the ADC in the controller?

Thanks!

img1: SO pin

 

img2: output voltage at motor pins (1 PWM duty cycle)

  • 0
    TI__Mastermind 37683 points

    Hi Fabrizio,

    I have a few questions:

    1. I am not able to see the scope screenshots you attached. Can you attached them again?
    2. Did you perform the evaluation with the DRV8701EVM or with your own board?

  • 0 in reply to Pablo Armet
    Prodigy 50 points

    Hello Pablo,

    Thank you for checking this out. I will try to attach the screenshots again, please let me know if you can see them this time.

    The board I'm using is self-made, not the EVM one. The FETs are BUK7K12-60EX (dual N-channel 60V, 40A, 9.3mOhm).

    SO voltage:

    Motor voltage:

  • 0 in reply to Fabrizio Frigeni
    TI__Mastermind 37683 points

    Hi Fabrizio,

    I am able to see the scope shots now.

    I think what you are seeing in the scope shots are oscillations which can appear due to the parasitic inductance and capacitance present on the board. These parasitics essentially can create LC circuits that cause the oscillations shown on the scope-shots. The oscillations on the motor voltage can also cause the SO voltage to spike as can be seen in the scope shots.

    Can you share with me the schematic and board layout? If you don't want to share publicly, you can send me a private message.

  • 0 in reply to Pablo Armet
    Prodigy 50 points

    Hello Pablo,

    Thank you again for being so nice. I am attaching a screenshot of the relevant part of the schematic here: it mostly follows the guidelines I found in the datasheet. I'll send you the detailed Gerber files in a private message because it is a customer project and cannot be publicly shared.

    Thank you,

    Fabrizio

      

  • 0 in reply to Fabrizio Frigeni
    TI__Mastermind 37683 points

    Fabrizio,

    We will move this conversation via private message. I will close this thread but feel free to reply if there is any information you wish to share publicly.