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DRV10975: Speed Cmd Buffer will not go below 40 in closed loop, even if speed cmd is lower than 40

Grant Bracht
Prodigy 80 points
Part Number: DRV10975

Hello,

I have been having trouble getting my DRV10975 to spin my motor at low speeds, high speeds work great but I need to be able to use more of the driver's range. My motor's ph-ph resistance is 0.7 Ohm, and inductance is 0.19mH. I used the tuning guide to get my registers to the values that they are at now. My programmed register values are:

DRV_0x20: 0xBD

DRV_0x21: 0x1A

DRV_0x22: 0x38

DRV_0x23: 0xEC

DRV_0x24: 0x68

DRV_0x25: 0xDB

DRV_0x26: 0x97

DRV_0x27: 0xE4

DRV_0x28: 0x0E

DRV_0x29: 0x98

DRV_0x2A: 0x2C

DRV_0x2B: 0x4E

Startup seems to work fine, and so does running the motor with speed cmd above ~50, but when I try to go lower the speed cmd buffer stops me.

Thanks for any help you can give

  • 0
    TI__Mastermind 24415 points

    Hi Grant,

    In general, tuning a Sensorless BLDC driver can be challenging at low speeds because the BEMF will be much lower at low speeds. What is the low speed in electrical Hz that you are targeting? Speed is buffering because you have the mechanical AVS enabled. Can you disable Mechanical AVS and try again? Also, can you tune the lead time? 

    Regards,

    Vishnu

  • 0 in reply to Vishnu Balaraj
    Prodigy 80 points

    The speed I'm going for is around 200-300Hz. I have disabled the AVS and I am able to get to the lower speeds, but when decelerating now the speed goes all the way to zero and exits closed loop, so I have to go through the startup process again. Is there any way to keep the speed from buffering on the low end while keeping the driver in closed loop control? I don't need to get to zero, just stopping at 200-300Hz would be perfect.

  • 0 in reply to Grant Bracht
    Prodigy 80 points

    I was messing with some other registers and I think I fixed my problem by disabling LockEn[5] (stuck in closed loop), with all other registers the same as the original register dump. I will keep this thread open for the next day or two to so that I can test more extensively, but thank you for your time and help.

  • 0 in reply to Grant Bracht
    TI__Mastermind 24415 points

    Hi Grant,

    Thank for letting us know. Please let us know if you need further assistance!

    Regards,

    Vishnu

  • 0 in reply to Grant Bracht
    TI__Mastermind 18981 points

    Hi Grant, 

    Closing this thread as it looks like the latest response has resolved your problem.

    Please help mark the thread as resolved if that's the case - and if further debug support is needed, you can click "Ask a related question" to re-open the topic. 

    Thanks and Best Regards, 
    Andrew