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DRV8711 Structure of Pre-Driver Fault

masahiko shimizu
Guru 11235 points
Other Parts Discussed in Thread: DRV8711

Hi

My customer is using DRV8711.
He has a issue of PDF.

Could you let me know structure of Pre-Driver Fault?
He wants to know information as Figure1 of the following.

http://www.ti.com/lit/an/slva505/slva505.pdf

Thanks,
Shimizu

  • 0
    TI__Mastermind 26065 points

    Hi Shimizu

    Could you ask customer to provide the following info?
    1. VM voltage
    2. All Registers states of DRV8711 when PDF happened
    3. Current level (Rsense)
    4. MOSFETs part number

    The PDF detect scheme can be described as following.

    We monitor the external FET’s gate to source voltage during on and off. We have an analog comparator to detect the voltage to see if the Vgs over or under 1V.
    If predriver is command the external FET to on, then after 2.2us, we will look the comparator output, if output is high, then no fault, otherwise flag a fault.
    If predriver is command the external FET to off, then after 2.2us, we will look the comparator output, if output is low, then no fault, otherwise flag a fault.

    So, if noise be captured when we sampling the pre-driver output at after 2.2us time, there could be a PDF error reported.

    The following measures could be help on reducing the xPDF error.
    1. Set the pre-driver current output ability to minimum for both high side and low side.
    2. Select low diode recover FET and reduce parasitic on the board.
    3. Lower VM voltage
    4. Add gate resistors to low sides MOSFETs

    Best regards,

  • 0 in reply to Wilson Zuo
    Guru 11235 points

    Hi Wilson

     Thank you for your support.

     Your answer is very good.

     I will confirm my customer all resisters state and thing of your advice.

     MOSFETs part number is CSD88537.

     VM voltage is 24V

     Rsense is 0.1 ohm

    Thanks

    Shimizu

  • 0 in reply to masahiko shimizu
    Guru 11235 points
    Hi Wilson

    Thank you for your support.
    I'm sorry.
    There are no answer mails of the register information yet from a customer.

    But I have an additional question.
    Could you answer this question?

    "If predriver is command the external FET to on, then after 2.2us....."
    Is 2.2us fixed time or fluctuated time?
    If this is fluctuated time, What is the influential parameter? (DTIME, TOFF, TBLANK...etc)

    Best regards
    Shimizu
  • 0 in reply to masahiko shimizu
    TI__Mastermind 26065 points
    The 2.2us is fixed and analog designed inside with the internal clock, non adjustable.

    Best regards,
  • 0 in reply to Wilson Zuo
    Guru 11235 points
    Hi Wilson

    Thank you for your support.
    I understood.

    Thanks
    Shimizu