• State Resolved
  • Locked Locked
  • Replies 4 replies
  • Answers 1 answer
  • Subscribers 30 subscribers
  • Views 5247 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

Original question:

DRV8711: how to use the direct PWM input mode to control the stepping motor

DRV8711: Detection time of stall condition

Takashi Onawa
Genius 13200 points
Part Number: DRV8711

Hi Team,

I want to know how fast TDR8711 can detect stall condition.

Could you tell me the min and max detection time?

Regards,

Takashi Onawa

  • 0
    TI__Guru 56650 points

    Onawa-san,

    Two parameters could be related to your questions:

    1. SDCNT: A programmable counter circuit allows the assertion of the STALLn output to be delayed until the back EMF has been sampled below the SDTHR value for more than one zero-current step. The counter is programmed by the SDCNT bits in the STALL register, and provides selections of 1, 2, 4, or 8 steps.

    2. SMPLTH: Back EMF is sampled on the tri-stated output pin at the end of SMPLTH time (TORQUE register bit [10:8]).

    If you set 2 steps SDCNT, the DRV8711 has to get 2 consecutive BEMF below the stall detect threshold to report stall condition.

    For each BEFM sample, we have to wait the motor drive running into zero-current step, And then, gets the value at end of SMPLTH setting team.

  • 0 in reply to Wang5577
    TI__Genius 13200 points

    Hi Li-san,

    Thanks for your prompt response on this.

    OK, I understood the detection time related to the two parameters.

    Sorry, I didn't understand well how much is min and max detection time from your answer eventually.
    Could you help my understanding me with a case study? 

    What is the min and max detection time for the following cases?
    Step Angle : 1.8 dgree
    STEP : 10kHz
    SDCNT : 00; STALLn asserted on first step with back EMF below SDTHR
    SMPLTH : 001; 100 µs

    Regards,

    Takashi Onawa

  • 0 in reply to Takashi Onawa
    TI__Guru 56650 points

    Onawa-san,

    "The time between step inputs must be greater than SMPLTH time for back EMF sampling." (Datasheet page 23)

    If the step rate is 10kHz, each step is 100us. SMPLTH time should be 50us.

    SDCNT=00: STALLn asserted on first step with back EMF below SDTHR. Back EMF is sensed during a zero-current step and at the end of 50us SMPLTH time.

    Assume the customer picks 1/8micro-step; the motor is stop or stuck at step 2 and the step pin pulse rate is 10kHz (each micro-step is about 100us), Running to next zero-current step needs 15 step pulses. So, the detection time is 15*100us+50us=1550us.

    Assume the customer picks 1/8micro-step; the motor is stop or stuck at step 2 and the step pin pulse rate is 10kHz (each micro-step is about 100us), Running to next zero-current step needs 15 step pulses. So, the detection time is 1*100us+50us=150us.

    From here we can see, SDCNT setting, where the motor stops, micro-step setting and step rate affects the detection time.

    BTW, I would like to set SDCNT=01 or up to avoid any back EMF sensing noise concern.


  • 0 in reply to Wang5577
    TI__Genius 13200 points

    Hi Wang-san,

    Thanks, I understood.

    Regards,

    Takashi Onawa