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DRV8824 decay input question

Scott Boone
Prodigy 60 points
Other Parts Discussed in Thread: DRV8834, DRV8824, DRV8818

I am looking at using the DRV8824 in a new design. I have experience with the DRV8834 which has a variable decay input based on the resistor value to ground that is placed on its input. The 8824 input is documented as either high (slow decay), low (fast decay) or open (mixed - fast for 75% of PWM cycle). Does the device support the addition of resistance to ground to change the mixed decay to something other than the 75% in a similar fashion to the  DRV8834 or is it limited to the only the one mixed type documented in the data sheet? I would like to be able to implement a 50% of PWM cycle with this part if possible. 

  • 0
    TI__Mastermind 20985 points

    Hi Scott, the DRV8824 mixed decay mode is indeed fixed at 75%.  However, the DRV8818 is a very similar device that has a fully programmable decay pin, as well as tOFF and tBLANK.  There's some data readily available here that shows current regulation with changing all 3 of those: http://www.ti.com/tool/TIDA-00111

    Best regards,
    RE

  • 0 in reply to RE
    Prodigy 60 points

    Just to clarify, I assume then that this means that selecting the 10K POT on the CPG004_DRV88XX evaluation module that is tied to the Decay pin should not be used with the DRV8824? This board is marked for use with the (DRV) 8802, 8812, 8813, 8814, 8824, 8825, 8841 and 8843 so I will assume that one or more of these has selectable decay modes.

    For now, I need many of the other features of the DRV8824 (step/dir control, higher voltage than the DRV8834, current control, microstepping) and the small package size to replace the DRV8834 we have been using in an older design. I will try to work around the decay issue for now.

  • 0 in reply to Scott Boone
    TI__Mastermind 20985 points
    I think you can still use the pot, to select 1 of the 3 digital settings. When the decay pin is <0.8V it's slow, ~1.5V is mixed, and >2V is fast.

    Best regards,
    RE
  • 0 in reply to RE
    Prodigy 60 points
    RE,

    Thank you for the assistance. I really appreciate it.

    Scott