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DRV8711: DRV8711DPC FAULT PIN ENABLE

Prodigy 70 points

Replies: 15

Views: 335

Part Number: DRV8711

Dear Sir,

               I am using DRV8711 to drive 4 motors on one PCB. When we do run-in mode before functional test. The fault pin active sometimes. We tried to adjustment the software and different PCB layout. But the situation still happens. Can someone help to solve this problem? Many thanks.

Jason  

  • Hi,

    Have you tried reading the SPI registers to see what type of fault is occurring? 

    Do you think you can share with me your schematic?

    Regards,
    Pablo Armet
    Motor Applications Team

  • In reply to Pablo Armet:

    Hi,

         The register shows over current error. Below are the schematics. DRV8711 DRIVER REV3.pdfDRV8711 DRIVER REV4.pdf

  • In reply to HK2245:

    Hi,

    Thank you for sending the schematic. I have a couple questions.

    • Are you seeing the OCP fault being triggered on all four IC's or just on certain ones?
    • Can you send me your SPI register settings?

    Regards,
    Pablo Armet
    Motor Applications Team

  • In reply to Pablo Armet:

    Hi,

         All 4 motors occurs fault signal. Motor1>>5%, Motor2>>10 %, Motor3>>25%, Motor4>>>60%. Below are the motor spec:

    Motor 1: 2.4VDC, 2A/PHASE, 1.2ohm

    Motor2,3,4:2.6VDC, 4A/PHASE, 0.65ohm, 2.4mH

    CTRL Resister: 0x0C34

    TORQUE Resister: 0x07FF

    OFF Resister: 0x0030

    BLANK Resister: 0x00FF

    Decay Resister: 0x0410

    STALL Resister: 0x0040

     DRIVE Resister: 0x006A

    Regards

    Jason

  • In reply to HK2245:

    Hi Jason,

    Pablo is not available today, so I am responding for him. Thank you for the additional information.

    There are a few register settings to address.

    First, please change the DECAY register to either 0x0510 (auto mixed decay) or 0x0310 (mixed decay) as a starting point.

    Then please change the BLANK register to 0x0180 (adaptive blanking and 2us TBLANK)

    The TORQUE register should be set to either 0x075D (.05Ohm resistor) or 0x0782 (.07 Ohm resistor). This should limit the current to 4A full scale

    These changes should help get you closer to your goal and hopefully remove the overcurrent faults. The overcurrent faults were probably due to a combination of setting the TBLANK too long and the TOFF too short.

    For more information, please see the Decay Mode Setting Optimization  and DRV8711 Quick Spin and Tuning Guide www.ti.com/.../SLVA632

    Best Regards,
    Rick Duncan
    Motor Applications Team

  • In reply to Rick Duncan:

    Hi  Rick,

                   Thank you for your reply. I will let our engineer to do more test when change the register. And we also notice a interesting thing. We change the MOSFET CSD88539ND to CSD88537ND. Suddenly the issue are solved without adjusting the register setting. Do you think any possibility the issue comes  from the MOSFET? And do TI have the recommended MOSFET list or how can we to select a suitable one? Thank you for your support.

    Jason

  • In reply to HK2245:

    Hi Jason,

    Changing to the lower Rdson FET reduces the VDS voltage, and is probably masking the OCP error.

    But the OCP threshold is set at 750mV, which equates to ~32A  (750mV/23mOhm) through the FETs. This is too much current and needs to be addressed.

    If you have a current probe you will probably see this large current for a short period of time.

    Best Regards,
    Rick Duncan
    Motor Applications Team

  • In reply to Rick Duncan:

    Hi Rick,

                 We tried to adjust the register you told us. But it's the same result. Is there any other solution?

    Regards

    Jason 

  • In reply to HK2245:

    Hi Jason,

    Do you have a current probe? If so, please provide a scope capture of the current through the windings just prior to the nFAULT signal asserting.

    This will help provide information on the cause.

    If you do not have a current probe, please provide a scope capture of the voltage across the sense resistor to GND prior to nFAULT asserting. This can be more difficult to interpret.

    Has the firmware engineer confirmed the registers writes?

    If the motor is not connected, do you get the OCP fault? If so, please check the layout.

    Best Regards,
    Rick Duncan
    Motor Applications Team

  • In reply to Rick Duncan:

    Hi Jason,

    Do you have any updates?

    Best Regards,
    Rick Duncan
    Motor Applications Team