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DRV10983-Q1: Constant Speed Control Algorithm Accuracy

Mitchell
Expert 4915 points
Part Number: DRV10983-Q1
Other Parts Discussed in Thread: DRV10987

Hi Team,

My customer is looking for some additional information around the constant speed control capabilities of the DRV10983-Q1. In their application this part will spin a motor at 3000 RPM.

This spec may or may not exist, but we'd like to better understand the controller's ability to maintain a constant speed with minimal "ripple" so to speak.

We see that there is some data in the BLDC Speed Regulation Reference Design that compares output speed matching to the set input command, but this doesn't quite tell us how this varies over time. 

Thanks,
Mitchell

  • 0
    TI__Prodigy 190 points

    Hi Mitchell,

    In order to maintain a constant speed with minimal ripple under different load conditions, a feedback loop needs to be implemented using an MCU. The TACH (FG pin) output or I2C output from the DRV10983-Q1 can be used to output speed feedback measurements. This measurement can be used to develop an algorithm, such as a simple PI controller, to ensure a constant, accurate speed.  There is another reference design for the DRV10987 that details a similar application as well.

  • 0 in reply to Mostafa Shubbar
    TI__Expert 4915 points
    Hi Mostafa,

    Thanks for the quick reply. This makes sense - the MSP430 is performing the PI control loop based on the speed feedback from the DRV10983-Q1.

    I was thinking that with this part, you could give it a PWM signal and have it do the control loop internally to the device. Is this not the case? Or is it just not going to have very good performance? Do we have any other -Q1 devices that offer this type of feature?

    Ideally, my customer is looking for the easiest way to get a motor to accurately spin at a desired RPM, with as minimal programming as possible :)

    Thanks,
    Mitchell
  • 0 in reply to Mitchell
    TI__Prodigy 190 points
    Hi Mitchell,

    The internal close loop mode uses the current in the U phase of the motor to estimate BEMF and control the drive state of the motor. This won't effectively regulate speed, and under load conditions the motor may actually spin faster than the input command. The PWM input actually doesn't correspond to the PWM output frequency that drives the motor phases. The PWM input is a digital input mode which will take the PWM duty % and convert it to a digital speed command. Depending on the application, the customer may need to implement some programming.

    Regards,
    Mostafa Shubbar