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How to use the drv8812 same DECAY pin to control different DECAY mode?

power lin
Prodigy 80 points
Other Parts Discussed in Thread: DRV8812

Hello Team,

drv8812’s  DECAY pin sets the decay mode for both H-bridges, so when I used drv8812 drive stepper motor  with  Micro Step to obtain a polarization waveform such as the one depicted in Figure (use slow decay during sine wave quadrants 1 and 3, and then fast or mixed decay on quadrants 2 and 4,use slow decay during cos wave quadrants 2 and 4, and then fast or mixed decay on quadrants 1 and 3.stepper motor )

I had a problem how to use same DECAY pin to control different DECAY mode?

Many Thanks

lin

  • 0
    TI__Mastermind 26065 points

    Hi Lin

    Usually you don't have to change decay mode during one step cycle. Although It is a good way that the use slow decay for the current increasing section and fast or mixed decay for the current decreasing section, keeping mixed decay all the time of DRV8812 will also be good during both the current increasing and decreasing section. if you watch the current waveform, you will notice that.

    The priciple of decay turning is to make the current waveform more "sine". Distortion problem happens to the decreasing section most of the time.

    Thanks.

    Wilson Zuo

    Motor Application Team

  • 0 in reply to Wilson Zuo
    Prodigy 80 points

    Hi Wilson,

    Thanks for the quick reply.In 8812‘s datasheet it say that  Mixed decay mode begins as fast decay, but at a fixed period of time (75% of the PWM cycle) switches to slow

    decay mode for the remainder of the fixed PWM period. can i change  mixed decay ratio?

    Thanks,

    lin