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MCT8329A: Speed Loop/ Power Limit

Ben Gelinas
Prodigy 100 points
Part Number: MCT8329A

Hello Gurus,

For my design I am using the MCT8329A.  I am using Speed Loop as my Closed Loop Mode as maintaining constant speed is important for my application. 

I would like to also set up a power limit.  As per the datasheet and empirical testing, it seems that Speed Loop and Power Limiting are mutually exclusive, is this correct?

Attempting to set a Max Power limit on my controller does not seem to have any effect on input power while in Speed Loop mode.  Adjusting Max Speed while in Power Loop mode seems to have no effect on speed control [motor just winds up terrifyingly fast]. 

Lost cause?  Any thoughts?

Thanks!

  • 0
    TI__Mastermind 24130 points

    Hi Ben,

    I will look into this and get back to you by EOD.

    Regards,

    Joshua

  • +1 in reply to Joshua Horlander Cruz
    TI__Mastermind 24130 points

    Hi Ben,

    Ben Gelinas said:
    it seems that Speed Loop and Power Limiting are mutually exclusive, is this correct?

    The Speed loop and Power loop modes cannot be used at the same time. If you want to have a power limit while operating with Speed loop we recommend setting the register CBC_ILIMIT to the maximum current you want to allow and use Cycle-by-Cycle current limit to create the power limit.

    Setting the Cycle-by-Cycle to a mode which does not report a fault yet puts the gate driver into recirculation mode will allow for the current to be limited without stopping the motor. 

    For more information on this function please see section 7.3.20.8 of the datasheet

    Regards,

    Joshua

  • 0 in reply to Joshua Horlander Cruz
    Prodigy 100 points

    Thanks for the reply.  I did consider this as an option, but the caveat is that my application demands comparable performance at varying voltages.  Naturally, the motor draws less current at higher voltages under the same load.  Based on my needs, and the performance of the motor, I would need only to limit the current at higher operating voltages.  This limit will negatively impact the performance at lower voltages, for which I do not have enough margin for.

    Your response is much appreciated, though unfortunately I do not believe this will work for my application.  

    Thank you!