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DRV8702-Q1: Current pulled low without fault

Frank QIN
Genius 9470 points
Part Number: DRV8702-Q1


Tool/software:

Hi Team,

When we are having test with DRV8702-Q1 and MOSFETs, the output current can be pulled low by some reason. Could you please share some insight on this?

We found this issue both with eLoad and real power resistance.

The current pulled low can keep for 42us, the nFAULT is high, IN pin are high. The yellow curve is MOSFET gate waveform, blue is nFAULT, pink is bridge current.

Thanks

Best,

Frank

  • 0
    TI__Mastermind 47775 points

    Hi Frank,

    Thank you for your question.

    I understand that fault pin keeps high, so no fault condition happens. And load is resistive, not motor.

    We need to have customer's schematic and how load is connected. And where waveforms are measured. 

    How they are operating nSLEEP/IN1/IN2 signals? Customer is better to confirm those input signals as well additionally when issue happens. It could be just result of IN1/IN2 changes.

    regards

    Shinya Morita

  • 0
    Prodigy 40 points

    Hi Shinya Morita,

              是按照nSLEEP=1、IN1=0、IN2=1进行配置的，电流采集的是桥臂输出电流，基本上电流超过13A就会出现这种情况。

  • 0 in reply to Shinya Morita
    TI__Genius 9470 points

    Morita-san,

    Allow me to translate customer's reply.

    It is configured as nSLEPP=1, IN1=0, IN2=1. The current sense is on bridge. It can happen when current larger than 13A.

    Frank

  • 0 in reply to Frank QIN
    TI__Mastermind 47775 points

    Hi Frank,

    Thanks. I am wondering those signals are toggling while seeing current drop. Current drop was caused by those signals toggle or dip or some changes.

    regards

    Shinya

  • 0 in reply to Shinya Morita
    Prodigy 40 points

    When the current drops, these signals do not switch and remain in one state.

  • 0 in reply to yan mengxin
    TI__Mastermind 47775 points

    Hi Frank,

    As previously requested, we need following info.

    >>>>We need to have customer's schematic and how load is connected. And where waveforms are measured. 

    2 ideas without schematic.

    1) Disable current regulation then see what happens.

    2) Disable OCP or chose 0.;96V then see what happens.

    regards

    Shinya

  • 0 in reply to Shinya Morita
    Prodigy 40 points

    Hi  Shinya Morita,

            1. The schematic diagram is shown in the figure. The indirect power resistance of the two pins X1-10 and X2-5 is tested. The grasping current position is indicated in the diagram.

            2.The two pins VREF and AVDD are joined together.

            3.When I tried 0.48V before, the same thing happened,0.96V let's try it again.

  • 0 in reply to yan mengxin
    TI__Mastermind 47775 points

    Hi,

    Thank you for your feedback. Will feedback to you about schematic later.

    quick note is "better to try Disabled", not only 0.96V. If issue goes away by "disabled", it is obvious that your behavior is result of the current regulation function.

    regards

    Shinya

  • 0 in reply to Shinya Morita
    TI__Genius 9470 points

    Hi Morita-san,

    I would like to jump in here. Disable the OCP is a workaround, while we are more curious on the root cause. If the behavior is caused by overcurrent, why the nFAULT was not assert? We suspect there is also some mismatch on OCP and nFAULT.

    Thanks

    Best,

    Frank

  • 0 in reply to Frank QIN
    TI__Mastermind 47775 points

    Hi Frank,

    Thank you for your questions.

    DRV8702-Q1 has two different functions. VDS over current protection(OCP) and Over current regulation(ITRIP). 

    I was suggesting to disable the over current regulation. over current regulation does not assert nFAULT. If OCP happens, nFAULT should go low.

    regards

    Shinya Moitra

  • 0 in reply to Shinya Morita
    Prodigy 40 points

    Hi  Shinya Morita,

           We have tried to disable OCP and ITRIP, but there is still a phenomenon of trouble-free current pulling down, there is no other solution.

    Thanks

    Best.

  • 0 in reply to yan mengxin
    TI__Mastermind 47775 points

    HI,

    Thank you for your questions. Let me try to squeeze idea here.

    1) MODE pin external resistance. 

      MODE pin input should be 0,1 or HiZ. Customer's schematic R641 is 10Kohm which could be detected as HiZ. Then DRV is in PWM mode. So IN1=0, IN2=1 is "Reverse" - current could flow.

     If customer do not want to have current during IN1=0, IN2=1, MODE pin pull to DVDD via 1Kohm. Then DRV will be under independent mode. 

      

    regards

    Shinya

    regards

    Shinya