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8711 decay mode settings

Ajay Nayak
Prodigy 70 points
Other Parts Discussed in Thread: DRV8711

Dear Sir,

I am facing setting problem of 8711. My motor is running but creates lot of noise & it gets heating

For 8711  setting  we need some guideline to set "decay mode  Vs micro-step Vs  motor RPM"

In earlier posts I found that  " Slow decay is more useful for  HALF / FULL step"

Similar way for different rpm can we come to rough conclusion that if RPM is so & so then we can set these settings....like that.

e.g.

1) For 0----100 RPM;--- use--____________ decay mode

2) For 100----300 RPM;--- use--____________ decay mode

3) For300----1000 RPM;--- use--____________ decay mode

Rising T-OFF or Reducing T-BLANK will taken place in second phase......like

e.g.  for_______ decay mode ;T-OFF= from_____to____ us.

It is sure that all above parameters are depend on Motor Inductance. and applied Voltage, but to start if we get basic guideline...it will be easier to fix the actual parameters. Otherwise lot of days we are spending on development  but nothing is concluding for this 8711 device !!!!

Regards

Ajay Nayak

Applied Electronics & Control Eng

  • 0
    TI__Guru** 114905 points

    Hi Ajay,

    Have you read the two documents that help in tuning:

    http://www.ti.com/lit/pdf/slva632 and

    http://www.ti.com/lit/pdf/slva637

    As you mentioned, there are many variables that affect the current waveform. Speed, voltage, and inductance are just a few.

    In general, it is recommended to start with automixed decay mode, and adaptive blanking set. If the motor operates as desired, you may be done. If you are trying to get more performance from the motor, the DRV8711 has the ability to tune many parameters as you have noticed.

  • 0 in reply to Rick Duncan
    Prodigy 70 points

    Dear Rick,

    Thanks for reply.

    I have already taken references of your all application notes.

    Here we have 2 cases:-

    1] Stepper Driver with its own speed setting:-

    => In this case system know  speed value...so we can use algorithm accordingly

    2} Stand alone stepper driver:-

    => In this case  end user is applying pulses to driver card to get desired speed. And speed is always changing.

    The issue arrives here. We don't have the control over speed & step_modes.

    That's why I was asking to get  some guideline to set  Decay mode / OFF Time / Blanking time according to RPM .

    As we are developer, we will keep continue our development. Let us hope will solve the issue asap.

    Regards

    Ajay Nayak

    Applied Electronics & Control eng.

  • 0 in reply to Ajay Nayak
    TI__Guru** 114905 points
    Hi Ajay,

    In case 2, are the motor parameters, the system voltage, min and max speed, and microstep settings known?

    All of these can effect the decay mode setting. The voltage and step modes can also effect the maximum speed of the motor.

    In most cases, we recommend automixed decay with adaptive blanking enabled.
    The blanking time can typically be set to 1us
    Off time can be set to 20 to 25us. This value should keep the PWM frequency above audible with lower switching losses.
  • 0 in reply to Rick Duncan
    Prodigy 70 points

    Hi Rick,

    The business of of Standalone stepper driver card--(specific-4.5A) is more than close loop speed control card. 

    We have successfully done the 8825 job of 2.5Amp capacity & floated in market very successfully.

    But the major business is of 4.5Amp & 6 Amp driver cards. The benefit of choosing 8711 is suitability to both capacity.

    --------------------------------------------------

    In CASE 2]---

    1) RPM range is -----1  to 1000 RPM

    2) Operating voltage --- +24VDC

    3) Microstep setting:--

        We are providing selection switches but  we need to provide guideline to end customer according to RPM requirement.which step mode is suitable.

     The  major problem  is at this stage. If we feed a standard table in our system which sets optimum setting according to RPM...the job will be easy.

    RPM value can be sensed by detecting micro-step mode setting & frequency of applied pulses.......

    This is my target......

    I will try by implementing your suggestion:-

    "In most cases, we recommend automixed decay with adaptive blanking enabled.
    The blanking time can typically be set to 1us
    Off time can be set to 20 to 25us."

    Regards

    Ajay Nayak

    Applied Electronics & Control Eng.