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DRV8323: Direction of current in shunt reverses

Alfred Logico
Expert 4630 points
Part Number: DRV8323

Hi Team,

My customer came to me with some questions on our DRV8323HRTAR for their design.
They found that the direction of the current in the shunt resistor reverses with each positive edge of the three Hall signals. This behavior does not occur with the negative edge:

They are using the DRV8323HRTAR with the 1xPWM mode.

Can you help me to understand this behavior? Are they doing something wrong? How can they solve this problem?

Thanks!

BR,

Alfred

  • 0
    TI__Genius 10221 points

    Hi Alfred, 

    Thank you for your question! Please let me look into the question and follow-up with an update or explanation this week. 

    Best Regards,

    -Joshua

  • 0 in reply to Joshua Maize
    TI__Expert 4630 points

    Hi Joshua,

    Good day!

    I was hoping to follow-up on this e2e post. Hope to get feedback from you soon.

    Thanks!

    BR,

    Alfred

  • 0 in reply to Alfred Logico
    TI__Genius 10221 points

    Hi Alfred! 

    Thank you for the patience in this delay. 

    Is there any filtering capacitors on the current sensing input and output?

    I'd also like if we could compare the measured current waveform with the phase current and voltages to determine further if this is a due to voltage transients.

    Best Regards, 

    -Joshua

  • 0 in reply to Joshua Maize
    TI__Expert 4630 points

    Hi Joshua,

    Let me check, they did share some recent updates.

    I just want to share two additional pictures we took with the oscilloscope.

     

    Signal assignment

    Yellow: PWM input signal

    Orange: Hall sensor 1 input signal

    Green: SOA output signal

     

    The first picture shows the already described issue with the positive peak (negative current through the measurement shunt).
    In the second picture one can see that this “commutation peak” obviously can also be negative (positive current through the measurement shunt).

    Can you explain this phenomenon?

  • 0 in reply to Alfred Logico
    TI__Genius 10221 points

    Hi Alfred,  

    Thank you for the additional info! Please allow me to look a bit further into this and follow-up with additional thoughts by the weekend  

    Best Regards,

    -Joshua

  • 0 in reply to Joshua Maize
    TI__Genius 10221 points

    Hi Alfred, 

    I apologize for the long delay during my external leave, but if this inquiry is still open please find my observation below: 

    This current spike appears similar to in/outrunning FET current based on the Hall input and PWM waveforms. Can we collect the phase voltage waveform on the fourth oscilloscope channel that would be helpful to confirms the exact source. 

    Also, are there any observable affects on motor operation with this current spike behavior? 

    Best Regards, 

    -Joshua