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DRV8323: Selection of a suitable gate series resistor with smart gate driver

Tobias Widmann
Prodigy 70 points
Part Number: DRV8323

While having a look at the reference designs I recognized that TIDA-00774 uses a series gate resistor (3R3) where TIDA-01516 dosen’t use one.

When researching into that direction I found some documents like "External Gate Resistor Design Guide for Gate Drivers" which address the selection of a series resistor, but not especially for smart gate drivers.

Do you have design guides or instructions how to select appropriate series gate resistors with smart gate drivers like DRV8323?

Thank you in advance

Tobias

  • 0
    TI__Genius 17611 points

    Hey Tobias,

     

    So, the appeal with smart gate drive technology is the ability to control your IDRIVE or the gate drive current.

     

    When selecting Idrive one must consider the slew rate or the rise/fall time of your MOSFET based on the following equation:

    Trise/fall = QGD / ISource/Sink

    We have seen customers use a rise/fall time of 100-200ns for a fast switching.

     

    Now gate resistors can be used to further limit the Idrive. So, it is dependent on the MOSFET selection and layout considerations etc. We recommend looking at the effective slew rate with default Idrive. And then adjust Idrive setting as needed. Then you can decide if you want to add gate resistor to further reduce gate drive current or to mitigate ringing if present.

     

    Best Regards,

    Akshay

  • 0 in reply to Akshay Rajeev Menon
    Prodigy 70 points

    Hello Akshay,

    so with smart gate driver you just recommend to increase series gate resistance if ringing of the gate-source voltage is detected?

    How does this increased series gate resistance affect unintentional gate switch on? Is there a difference in the applied ISTRONG or is that always regulated to 2A maximum?

    Referring to application brief "Driving Parallel MOSFET using the DRV3255-Q1" pre gate resistors placed for each FET individual are recommended to achieve similar switching behavior of parallel FETs. How should they be dimensioned?

    Is there a maximum recommended series gate resistance to insure proper operation of the DRV?

    Thank you for your fast response.

    Kind regards

    Tobias

  • +1 in reply to Tobias Widmann
    TI__Genius 17611 points

    Hey Tobias,

     

    I would suggest adding gate resistance if the MOSFET slew rate is too fast and if there is ringing.

     

    Yes, the added gate resistance should reduce the chance of unintentional gate switch on.

     

    I would recommend adding gate resistance if lowering the Idrive is not enough to prevent accidental turn on or if there is shoot through.

     

    The ISTRONG will be lower than 2A if there is a gate resistor.

     

    For parallel MOSFETs, I would suggest using the same resistance for each FET. But the actual value of the resistance will depend on your specific design and observed slew rate.

     

    Hope this offers some clarification.

     

    Best Regards,

    Akshay