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DRV8323R: nFault Pin goes low at higher current draws

ANIKET SHIGWAN
Prodigy 40 points
Part Number: DRV8323R
Other Parts Discussed in Thread: DRV832X

Hello, I am testing the DRV8323RHRGZR Hardware device to drive a 3 phase BLDC motor in 1x PWM Mode.  I have shorted the VDS pin to GND so that VDS trip point = 0.06V. That corresponds to around 20A. The motor rotates fine without any Faults raised. When the motor is loaded and the current rises nFault LED starts blinking. I have added a FUSE of 6 Amps in series to the Driver supply. The FUSE is intact when this occurs. So I believe that the current is well below 20A trip point.

Because of the nFault trigger the motor rotation is not as smooth as the unloaded Motor rotation. I tried raising the IDRIVE settings as well but no change observed in the nFault LED behavior.

  • 0
    TI__Expert 3020 points

    Hi Aniket,

    Thank you for posting this question! To clarify, have you attached the fuse in series with the VM pin of the DRV8323RHRGZR, or to the overall power supply's positive lead?

    Thanks,

    Davis

  • 0 in reply to Davis Jackson
    Prodigy 40 points

    The fuse is attached in series with the overall supply. The system is 48V.

  • 0 in reply to ANIKET SHIGWAN
    TI__Expert 3020 points

    It does seem that there is not a current draw over 6 Amps, but the nFault could be caused by another event occurring, such as a VSense overcurrent fault. Please refer to this FAQ on debugging hardware drivers, especially the sections on VDS and VSEN Overcurrent: https://e2e.ti.com/support/motor-drivers-group/motor-drivers/f/motor-drivers-forum/1160331/faq-debugging-faults-with-hardware-variant-devices. Additionally, you can check whether there are any supply voltage spikes over the max rating of the device which might be causing issues, although I suspect this is not the issue.

  • 0
    Genius 5040 points
    ANIKET SHIGWAN said:
    When the motor is loaded and the current rises nFault LED starts blinking. I have added a FUSE of 6 Amps in series to the Driver supply. The FUSE is intact when this occurs. So I believe that the current is well below 20A trip point.

    Hi,

    Many fault condition can trigger the nFAULT pin, so you need to find out the root cause and it might not be the FET VDS issue. With higher load, could the the supply under voltage that triggered the fault.

    From datasheet:

    "In addition to the high level of device integration, the DRV832x family of devices provides a wide range of integrated protection features. These features include power supply undervoltage lockout (UVLO), charge pump undervoltage lockout (CPUV), VDS overcurrent monitoring (OCP), gate driver short-circuit detection (GDF), and overtemperature shutdown (OTW and OTSD). Fault events are indicated by the nFAULT pin with detailed information available in the SPI registers on the SPI device version."

    Brian

  • 0 in reply to Brian Dang
    Prodigy 40 points

    I experimented with different VDS settings and found that the nFault Pin goes low at different values of current. I want my system to trip / report Fault at around 20A current draw. Can you please suggest me how to select the appropriate resistors for the same.

  • 0 in reply to ANIKET SHIGWAN
    TI__Expert 3020 points

    Please refer to this table from the datasheet explaining how to select a VDS trip voltage:

    To convert the VDS trip voltage to the current level you want, please refer to the Rds(on) value of MOSFET you are driving.

    The VSEN trip voltage is set at 1V for the hardware variant:

    You can choose your current shunt resistor per the current level you want to set. I would still recommend going through the Fault debug process mentioned earlier to confirm whether an overcurrent situation is causing the fault or if there is another issue.

  • 0 in reply to ANIKET SHIGWAN
    Genius 5040 points
    ANIKET SHIGWAN said:
    I experimented with different VDS settings and found that the nFault Pin goes low at different values of current. I want my system to trip / report Fault at around 20A current draw. Can you please suggest me how to select the appropriate resistors for the same.

    Again, the nFAULT might be not triggered by the VDS setting, but by other causes such as supply under voltage. How do you know nFAULT was triggered by VDS and not something else?

    Brian

  • 0 in reply to ANIKET SHIGWAN
    TI__Expert 3020 points

    Hi Aniket,

    Please mark this thread as resolved if the resources provided helped solve your issue, or let us know if you still have questions.

    Best,

    Davis

  • 0 in reply to Davis Jackson
    Prodigy 40 points

    Hello David,  While trying to probe the above mentioned quantities, a pair of MOSFETS shorted with GND. WIll need some time to order replace and test the above mentioned solutions.

  • 0 in reply to ANIKET SHIGWAN
    TI__Mastermind 18981 points

    Hi Aniket,

    Do you still require further assistance on this?
    Please help mark the thread as resolved if there are no further questions. Thanks.

    Best Regards, 
    Andrew