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Original question:

DRV8705-Q1: Overcurrent fault behavior

DRV8705-Q1: Overcurrent fault behavior

sonali zodage
Intellectual 280 points
Part Number: DRV8705-Q1

Hello Murugavel,

We are utilizing the CSA output analog voltage information, converting it to digital using the MCU ADC, and determining whether the current exceeds the set threshold or not.

Currently, we have configured a 25A current threshold through the internal ADC in the firmware. Below is the overcurrent waveform of the motor.

My question is, we have observed the motor current increasing up to 49A while we have set the threshold at 25A. Why is there an increase in current after the overcurrent triggers? Our client has been monitoring the logs, and they indicate that sometimes the maximum current increases up to 30A. Since we have set the threshold at 25A and the logs show higher currents, we need a clear explanation as to why the current is exceeding the set threshold.

Thanks,

Sonali

  • 0
    TI__Mastermind 28315 points

    Hi Sonali,

    Thank you for your question. 

    Could you start with "To team or just hi" from next time and do not put someone in our team like Murugavel? Each thread is assigned to someone from our team member based on the situation.

    In VDS over current function, DRV cannot monitor the motor current directly. Therefore DRV is monitoring VDS voltage on external FET.  

    1) If proper VDS_LVL is not set based on external FET's Rdson, DRV does not activate over current shutdown. Easy trial is to reduce VDS_LVL setting from what you are setting now (For example, half or 0000b=0.06V)

    2) If DRAIN pin and SH is not connected to external FET's Drain and Source like above, over current protection does not work correctly.

    3) If VDS_MODE is set 10 or 11, DRV does not stop driving even if hitting over current level. 

    regards

    Shinya Morita

  • 0 in reply to Shinya Morita
    Intellectual 280 points

    Hello,

    We are getting overcurrent triggers at 25A, but after triggering, there is a sudden increase in the current (up to 49A) before it reaches zero. I would like to understand why there is an increase in the current after the overcurrent is triggered. Please see the above waveform.

    Thanks,

    Sonali

  • 0 in reply to sonali zodage
    TI__Mastermind 28315 points

    Hi 

    Thank you for your questions. In order to do this debug, we need to check nFAULT pin together. This is common way for this type of debug.

    Capture SH pin(Motor current) with current probe together with nFAULT pin like bellow. The timing nFAULT goes low, it is timing of overcurrent trigger. Then we can check exactly where over current is triggered. 

    It could be around 49A instead of 25A. Normally motor current does not goes up after nFAULT goes low by VDS overcurrent detection.

    However, if your system has some different setting on 2)-3) of my previous post, situation will be different. I recommend to check 2) and 3) first.

    regards

    Shinya Morita