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DRV8308: controlling the acceleration when using the register speed control method

Earl Smith
Prodigy 20 points
Part Number: DRV8308

The motor is a single pole, 57000 rpm with hall effect sensors.  The motor is capable of ramping in speed at 400rpm/ms.  If I change speed in small incremental steps, there is no problem, but if I make a 50% step the motor will not respond to the faster commutation, and the motor makes noise and is spinning at an incorrect rotational speed.

What DRV8308 parameters should I adjust to correct the speed ramp time? 

  • 0
    TI__Mastermind 21805 points

    Hi Earl,

    I would recommend trying the following - although this device is classically very tricky to tune for some motors.

    • Increasing SPDREVS: allows for a more forgiving change in speed
    • Increasing SPEEDTH: allows for a more forgiving change in speed
    • Decrease INTCLK (increase the register setting): Results in a lower speed loop bandwidth that may more gracefully respond to a step function
    • Decrease SPDGAIN: less aggressive loop for change in speed
    • Decrease LOOPGAIN: less aggressive loop for change in speed
    • Try to bypass the compensator with BYPCOMP: check if the compensator setting is causing issues

    Thanks,

    Matt

  • 0 in reply to Matt Hein
    Prodigy 20 points

    The application does not use clkin and we we do not provide a frequency input or PWM input.  This design relies on setting the speed register to provide the speed setpoint.  Changing the parameters you suggested does not appear to make the desired change to the motor speed ramp.  What are the next steps to resolve this issue?

  • 0 in reply to Earl Smith
    Prodigy 20 points

    I would think setting gains to 1 would effectilvely remove those gains and should slow the ramp by changing the slope of the response.  It does not appear to affect the speed...not sure why...

  • 0 in reply to Earl Smith
    TI__Mastermind 21805 points

    Hi Earl,

    When using the register to set the speed, I think the speed loop is disabled. To use the speed loop, I think CLKIN is the only method of control available on the DRV8308.

    Thanks,

    Matt