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DRV8308: DRV8308 nLock reports lock, but loading the motor proves that it's not in fact locked

Rob Oppen78
Prodigy 170 points
Part Number: DRV8308

Hi,

I'm seeing an issue where the DRV8308 nLock pin is reporting lock (low), but if I load the motor and monitor FGout, FGout will stretch. This is in Clock Frequency Mode, speed is set to 300 and at a frequency of 50Hz, which translates to 750RPM.

  • 0
    TI__Genius 14487 points

    Hi Rob,

    Are you evaluating this functionality on our DRV8308EVM? Did you follow the steps for tuning Clock Frequency Mode from our User Guide? There are some filters and other features that need to be tuned for Clock Frequency Mode to work well.

  • 0 in reply to James Lockridge19
    Prodigy 170 points
    Hi James,

    Thank you for your response! I am using the DRV8308EVM for evaluation. I have tuned for Clock Frequency Mode, but I'm still confused why the DRV8308 would report lock when it is not locked?

    Also, is the SPEED parameter used for open and closed loop operation? The user's manual states that its the open-loop gain, but clearly influences operational behavior when in closed loop. For example, I've noticed that a larger SPEED value will increase the amount of current the system will sink in order to maintain speed loop lock.

    Thank you,
    Rob
  • 0 in reply to Rob Oppen78
    TI__Genius 14487 points
    Rob,

    What is your SPEEDTH setting? Can you try reducing it? This sets the allowable variation between FGOUT and CLKIN for LOCKn.