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MCF8329A: Regarding BUS CURRENT resister

Daisuke Higa
Genius 3765 points
Part Number: MCF8329A

Hi support team.

I have a inquiry regarding BUS CURRENT resister.

I use EVM to adjust the motor rotation.

Therefore, I am monitoring the BUS_CURRENT register (40Eh), which is a read-only register of the device, but the value remains 0.

What does the value of this register indicate?

Also, if the value of CSA_GAIN_FEEDBACK in the calculation formula of the data sheet is 5V/V, should I substitute 5? (Or is it 0 because it is 0h?)

As someone posted, my motor loses synchronization and stops because it cannot output the current set by the BASE_CURRENT register. Especially when starting rotation.

Currently BASE_CURRENT is set to 20A, but the measured value is 9A.

I was investigating the BUS_CURRENT register to find out why, but please let me know if I missed the point in my investigation.

Best regards,

Higa

  • 0
    TI__Genius 15320 points

    Hi Higa-san,

    Please allow me some time to look into your questions. I will get back with you by Wednesday.

    Regards,

    Joshua

  • 0 in reply to Joshua Horlander Cruz
    Genius 3765 points

    Hi Joshua-san

    Do you have any update?

    As we proceeded with additional verification, the values of Iq and Iq_ref were always 0 on the GUI.

    This seems like a GUI issue.

    I heard from you the other day that some GUI fixes are planned for this month.

    When in February will the revised GUI be released?

    Constantly manually monitoring the I2C code is a burden on the customer.

    Best regards,

    Higa

  • +1 in reply to Daisuke Higa
    TI__Genius 15320 points

    Hi Higa-san,

    Daisuke Higa said:
    if the value of CSA_GAIN_FEEDBACK in the calculation formula of the data sheet is 5V/V, should I substitute 5? (Or is it 0 because it is 0h?)

    In the BASE_CURRENT calculation you substitute the gain (V/V) value so in the case that you mention, 5 would be used in the calculation.

    The BUS_CURRENT register is the measured value of the bus current. This value's accuracy will depend on the external Shunt resistor and CSA combination used.

    For the limit at 9A, can you verify what values that are being set by ILIMIT, OL_ILIMIT, and ALIGN_OR_SLOW_CUR RENT_ILIMIT? All these values are set as percentages of the value written into BASE_CURRENT, so if you have 20A written to BASE_CURRENT then having a setting of 40% on ILIMIT will limit the max output current to 8A. 

    We recommend setting BASE_CURRENT to the max peak current rating of the motor. To get the best resolution from the internal CSA of the phase current, we also recommend determining a good shunt resistor value and CSA gain combination for the equation Peak Max Motor Current = 1.5/(CSA_GAIN * Rshunt).

    Daisuke Higa said:

    I heard from you the other day that some GUI fixes are planned for this month.

    When in February will the revised GUI be released?

    If I did state that we will be releasing a Motor Studio update in February then I was mistaken. We are currently working to update Motor Studio but we do not have a committed release date at this time.

    Regards,

    Joshua