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DRV8306: EVM: New thread - what is the purpose of the 0.01uF cap from VM to ISEN?

Nicholas Carley
Genius 9895 points
Part Number: DRV8306

This is a continuation of this thread:https://e2e.ti.com/support/motor-drivers/f/motor-drivers-forum/997475/drv8306-evm-what-is-the-purpose-of-the-0-01uf-cap-from-vm-to-isen/3684830#3684830 

There are differences between the article and design used at the evaluation board:

  • On the Evaluation board, you put the bulk from VDRAIN to GND; small caps between VDRAIN & SLA, and no cap on the sense R. That’s not matching what  said in the article.
  • The article suggests the bulk capacitor between VDRAIN and SLA and a small capacitor at the sense resistor.
  • My original design had both bulk (100uF) and small (0.1uF) between VDRAIN (V24V) and SLA (ISEN). I changed it after looking on the eval board schematics.

Which way is correct?

Thanks,
Nick

  • +1
    TI__Mastermind 21805 points

    Hi Nick,

    Thanks for your question!

    The article recommends a capacitor from VDRAIN to SLA in order to mitigate parasitic inductance; note this is not the main bulk capacitance to support the motor. In the article I use a large value of 10uF for my VDRAIN to SLA capacitor, but I have seen values of 0.01uF to 1uF used in practice. A rule of thumb is 2uF/W (watts of motor power) is for a large bulk capacitor in the system.

    Normally the bulk capacitance is tied to GND proper in order to source high current through the sense resistor when switching.

    Things can get a little confusing here, since the bulk capacitor does help stabilize any oscillations at VDRAIN, but the VDRAIN to SLA capacitor is then needed to stabilize oscillations at SLA.

    The article should not be recommending you to put a capacitor between SLA and GND (i.e. across the sense resistor), but some pictures may have a capacitive component in the diagram to indicate parasitic elements in the system.

    Thanks,

    Matt