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DRV8811: peak current difference between AOUT and BOUT

Yusuke Mukuno
Expert 7395 points
Part Number: DRV8811

HI Expert,

My customer find the peak current on both AOUT and BOUT.

1. Could you please let me know the reason of this peak current?

2. Also, could you please let me know the reason of difference peak current between AOUT and BOUT?

  • 0
    TI__Mastermind 23080 points

    Hello,

    What is the peak current it is drawing, and is the motor under load at this time?  

    Is it possible that one of the probes isn't calibrated and this is a false reading? 

    It would also be helpful to know some of the settings used in the driver - is this occurring with microstepping or the non-circular step mode, what is the input voltage, and what are the current regulation settings/schematic? 

    Regards,

    Jacob Thompson

  • 0 in reply to Jacob Thompson
    TI__Expert 7395 points

    Hello Jacob-san,

    Sorry, Customer miss-informed about part#.

    DRV8885 > DRV8811 (correction)

    is this occurring with microstepping or the non-circular step mode,

          > Full step : USM0=USM1=0

    what is the input voltage,

         > 25V +/-10%

    what are the current regulation settings

        > Itrip was set 600mA

    Motor was rotated continuously at this mesurement. (low torque)

    Motor infomation

    Type PM type
    Step angle 7.5
    Number of steps 48
    Static angle error 7%
    Step angle error -
    Maximum self-starting frequency 550 pps
    Maximum countinuous response frequency 3650 pps
    Maximum Static torque 31 mNm
    Non-excited holding torque 10.3 mNm
    Pullout torque 21 mNm
    Winding method Unifiera
    winding resistance 3.9 Ω/phase
    Winding inductance 4.3 mH/phase

    Also they tried to check about current probe, replace A and B, mesuremet point, caliblation, etc.

    The current probe and mesurement method don't have any problem.

    Thanks

    Muk

  • 0 in reply to Yusuke Mukuno
    TI__Mastermind 23080 points

    Hello,

    Please check the state of the SRn pin.  The note in 7.3.3 Decay Mode details that if the SRn pin is high the current is always in fast decay mode which is what we appear to see in the scope picture. This issue is unrelated to the current trip settings.  

    Please repeat the experiment but swap the motor phases A and B from the motor to the driver board.  We suspect this issue is because of an inductance imbalance between the two motor phases.  Swapping phase A and B on the motor driver output should swap which signal is going higher than the other.  I also recommend trying with a different motor sample to see if this motor is just an outlier with an inductance imbalance.  

    Regards, 

    Jacob 

  • 0 in reply to Jacob Thompson
    TI__Expert 7395 points

    Hello Jacob-san,

    Thank you for your comment.

    I checked to customer, SRn is low.

    I will try to discuss about Swapping phase A and B on motor driver with customer.

    Mukuno 

  • 0 in reply to Yusuke Mukuno
    TI__Mastermind 23080 points

    Thanks Mukuno-san,

    Looking forward to the update. 

    Regards,

    Jacob

  • 0 in reply to Jacob Thompson
    TI__Expert 7395 points

    Hi Jacob-san,

    Customer try to test swapping Aout and Bout.

    AOUT > BOUT, BOUT > AOUT

    The peak current of Bout was bigger than Aout.

    It seems to depend on motor inductance

    Could you please give me your comment about root cause.

    Thanks

    Mukuno

  • 0 in reply to Yusuke Mukuno
    TI__Mastermind 23080 points

    Hey Mukuno,

    Let me ask my team members with more experience and get back to you within 24 hours.  

    Regards,

    Jacob Thompson

  • 0 in reply to Jacob Thompson
    TI__Mastermind 23080 points

    Hey Mukuno,

    The current inductance is causing the current to run away.  Try setting SRn to HIGH to use fast decay mode and the current shouldn't increase as much at the end.  We agree that the issue is related to motor inductance.  

    Regards,

    Jacob