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DRV8811 Decay Mode Select

Mike Tucker
Prodigy 90 points
Other Parts Discussed in Thread: DRV8811, DRV8811EVM

Hi,

I am a new user of the DRM8811.  What determines the Decay Mode that I should select for my application?

Thanks,

Mike

  • 0
    TI__Guru 55605 points

    Mike,

    This is completely dependent on your motor specifications and speed/torque requirements.  The good news is, the DRV8811 gives you a lot of knobs to turn in terms of the time spent in fast vs. slow decay, blanking time, and off time.  These parameters are adjusted with resistor dividers on the DECAY pins or discrete RC components on the xRC pins.  Figure 3 in the datasheet show the parameters that are adjustable.  

    Our available EVM and GUI allow you to adjust the DECAY mode with a slider to optimize your torque ripple at your desired speed and max. torque settings.  I would suggest starting with the EVM as a prototyping tool and you can look down your design from there.  

  • 0 in reply to Ryan Kehr
    Prodigy 90 points

    Hi Ryan,

    Thanks for your reply today.  I do have the DRV8811EVM up and running and have been evaluating my motor.  I am new to stepper motor driver design and theory.  My stepper motor is sold by Applied Motion Products--Model # is HT17-275. Link: http://www.applied-motion.com/products/stepper-motors/ht17-275  I have a 12VDC supply.  The motor is wired in the series bipolar configuration.  The motor is working fine in my application at a setting of 700 steps per second (about 210 RPM).  I have been playing with the "Current Control" parameter on the EVM and with the "Decay Control".  I can't tell any difference in motor operation when I move the Decay Control from one extreme to another--thus my reason for asking "How do I know how to set the decay parameter?"  Can you tell me more about optimizing torque ripple?  I have connected the scope across the 0.5-ohm sense resistors...  I need some guidance how to set the current (i.e. Vref) and the decay for my system.

    Thanks for your help,

    Mike

  • 0 in reply to Mike Tucker
    TI__Mastermind 26065 points

    Hi Mike

    700 steps 210 rpm, So, you may use full step driving with a 1.8 degree motor, right?

    Decay mode setting usually plays obvious effect on high degree microstepping, such as 1/4 to 1/256. It is true that you can hardly tell any defference in full step as the decay mode changes.

    For more about the decay modes setting, you can first refer to most of the DRV8x datasheet including DRV8811 and understanding the fast, slow, mixed decay function. The reason and purpose we do defferent dacay modes setting is to let the current go down or up as quickly as possible according to the setting value determined by Micro stepping index. Usually, if the current is regulated the more sinusoidal, the more smooth running, and less noise and torque ripple.

    Generally,

    fast decay usually is needed for high indutance motor, high running speed, high degress micro stepping which all need the current change quickly. but fast decay brings audio noise sometime, also more heat and switching loss.

    Slow decay will have less audio noise and better output torque level at low speed running.

    Mixed decay will play in between and usually give good total effects on torque and noise and speed coverage.

    Thanks.

    Wilson Zuo

    Motor Application Team

  • 0 in reply to Wilson Zuo
    Prodigy 90 points

    Thank you Wilson for your comments.  Yes, I am running in full-step mode with a 1.8 degree motor.  Can you summarize the best settings for the highest torque at 12 VDC motor voltage?  I do not need precision steps so I am guessing that the highest torque at 700 steps per second would be achieved using full steps with slow decay?

    Mike

  • 0 in reply to Ryan Kehr
    Prodigy 90 points

    Ryan, Wilson:

    Thank you Wilson for your comments.  Yes, I am running in full-step mode with a 1.8 degree motor.  Can you summarize the best settings for the highest torque at 12 VDC motor voltage?  I do not need precision steps so I am guessing that the highest torque at 700 steps per second would be achieved using full steps with slow decay?

    Mike