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PGA411-Q1: Automatic Input-Offset Correction blocking angle output

Aleksander Polutnik
Prodigy 30 points
Part Number: PGA411-Q1


Dear

 

We are planning to use yours PGA411 as resolver interface for new motor controller intended for aerospace application. After reading datasheet I found one major issue: Note on page 26 in datasheet says, that Automatic Input-Offset Correction will be active 200-400 us each 100 ms and that during this time angle/velocity output is not active / frozen to last value. This is not acceptable for us, because it will generate instability in FOC control loop. Is there an option to disable this feature or how to get continuous angle output?

 

Regards

 

Aleksander Polutnik

  • 0
    TI__Guru 74322 points
    Aleksander,

    The appropriate applications engineer has been notified of your post and will respond accordingly.

    Regards,
  • 0
    TI__Mastermind 23810 points
    Aleksander,

    The automatic offset calibration cannot be turned off, so it will occur every 100ms. The actual length of the calibration routine is about 200us.

    It is possible to know exactly when the calibration routine is running by monitoring the ORDCLK pin. Normally, ORDCLK will have a rising edge every 100ns to signal when new data is available on the parallel output interface. There are only three times when ORDCLK will stop:

    1. If INHB is held low, meaning that the MCU has asked the parallel output interface to temporarily stop updating.
    2. There is a fault that caused the tracking loop to be disabled (indicated by the Fault pin as well as the fault status registers)
    3. automatic offset calibration is running

    So if there is no fault and the MCU is not holding INHB, then a non-switching ORDCLK means that the auto-calibration routine is running. You can use this method even if you are not using the rest of the parallel interface.

    Thanks,

    -Clancy
  • 0 in reply to Clancy Soehren
    Prodigy 30 points

    Hello

     

    This is mayor drawback for our application. Angle data is missing for 3 FOC cycles. This will require software observer in CPU SW.

     

    Thank anyway for help

     

  • 0 in reply to Aleksander Polutnik
    TI__Mastermind 23810 points
    Aleksander,

    We found an error in the PGA411 datasheet related to your question (and in my previous answer). The angle and velocity output from the PGA411 continues to be updated and is valid during the automatic offset calibration routine. The routine takes longer than we originally said (about 2.3 ms), but the tracking loop should continue working correctly the whole time.

    My apologies for the mistake. We are fixing this in the datasheet.

    Thanks,

    -Clancy
  • 0 in reply to Clancy Soehren
    Prodigy 30 points

    Dear

    Sorry, too late. Competitor part already soldered to PCB.

    Maybe next time.

    Regards

    Aleksander Polutnik