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DRV8308: tune the registers

Part Number: DRV8308

Hi everybody,

I am working with a DRV8308 and i have achieved to make it work quite well, but still want to solve an issue which happens at low speeds.

I am controlling a motor which is inside a mechanic reductive thing and this mechanic thing is coupled to a load. This load is 100N of resistive torque, right?

When the motor tries to move, it does but it must do at more than 250rpm otherwise it starts moving but only during a few seconds (less than a turn).

Please how can i adjust or tune the registers so i can make it work at 200rpm?

The registers setting is:

0x00-------24577

0x01-------1

0x02-------1204

0x03-------57218

0x04-------687

0x05-------12289

0x06-------33168

0x07-------300

0x08-------200

0x09-------500

0x0A-------62040

0x0B-------3500

By the way i am not sure what is the importance of the poles and zeros. Can anybody explain it a litte bit?

Thanks and best regards

  • Hi Alberto,

    Our expert has been contacted and should reply soon.
  • Hi Alberto,

    1. Try adjusting the AG_SETPT and AA_SETPT registers to a value less than your target minimum speed.
    2. Tune the ADVANCE value for better low-speed performance
    3. adjust the LOOPGAIN and SPDGAIN values for better low-speed performance

    These are some good starting points for getting the motor to spin during slow-speed operation.

  • Hi Phil,

    i didn't say that i am working in clock frequency mode

    The minimun speed i want to achieve is 200rpm (10Hz)

    As for your suggestions:
    1- AA_SETPT is already set to 0, and if AG_SETPT is less than 191 Hz, the motor starts spinning in a discontinuous mode, like little starts and stops but in the end it stops cause the torque is too high, though the current is not so
    2- With ADVANCE value, it happens the same issue (discontinuous mode). But in this case, if it is not 0
    3- LOOPGAIN is at it's max (1023) and SPDGAIN also must be 0

    What about the poles and zeros?
    I have tried to set them as the excel (Filter calculator.xls) of the user's guide says but i am not able to tune them. I don't see any progress.
    Any proposed values???

    Thanks and best regards
  • Sorry Phil,

    With SPDGAIN = 0 The speed is the double than the target speed. So actually, the motor was spinning at 500rpm instead of 250rpm.
    I have configured the SPDGAIN = 1

    Should i tune poles and zeros if i modify AGSETPT register?

    Thanks and best regards
  • Hi Alberto,

    You may need to modify poles and zeros, but my advice would be to first change the AFSETPT and then retune the FILK and COMPK registers as needed.

    For suggested values on the COMPK and FILK registers, I would start with the defaults that are pre-loaded in the GUI and then adjust from there.
  • Hi phil,

    Ok thans!
    I have changed the AGSETPT to 12Hz and tuned the LOOPGAIN to 33 so now the motor is spinning quite well at 250rpm.
    In order to make the motor spin at 200rpm....once AGSETPT is set to 6Hz..........could you give me guidelines of how should i modify the values on the FILK and COMK registers?
    I can't make the motor spin propperly at 200rpm with a 100N torque.

    Thanks a lot and best regards
  • Hi Alberto,

    We often recommend adjusting the FILK and COMPK register values by +/- 10 until you find a combination that is well fit to your application.

    I would also recommend adjusting SPDGAIN and ADVANCE for your application to see if you can better tune your motors performance.
  • Hi Phil,

    We have a motor consuming about 2A at 3000rpm with no load connected. It is too much
    I have been tunning the registers in order to make this consuption lower unsuccessfully.
    Is there any combination to achiev this?

    The motor is a 2p = 6, 24Vdc, 240W

    Any help will be apreciated.

    Thanks and best regards
  • Hi Phil,

    The motor had something wrong. We could get another one and that is OK.
    Thanks