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DRV8889-Q1: Stall Detection

Songzhen Guo
Intellectual 2840 points
Part Number: DRV8889-Q1

Hi Experts,

Nice to talk with you.

DRV8889-Q1 is under evaluation on customer side. there are two question from customer, could you give a suggestion on those questions? Thanks.

1. When the stall mode is 7, EN_STL =1. When the TRQ_Count is less STall_TH, the DRV8889-Q1 is not report he stall issue;

2. When STL_LRN=1, run the stepper motor according to the operation in the document, but the stall learning cannot be completed.

This is the first time for me to lean stepper motor driver, please be free to let me know your questions. Thanks.

Best Regards

Songzhen Guo

  • 0
    TI__Mastermind 44525 points

    Hi Songzhen,

    Thanks for the post. What are operating parameters of the application VM voltage, IFS full scale current, uStep mode, step rate PPS. What is the motor winding DC resistance DCR and inductance specification? Can we get a capture of the motor current waveform? Without any of those information we cannot say for sure what was going on. But based on our experience it appears that the motor or its operating conditions are not compatible to produce reliable TRQ_Count. Also please let us know what is the torque count at the steady state motor velocity. 

    Please also review this application note https://www.ti.com/lit/an/slvaei3/slvaei3.pdf . 

    Regards, Murugavel

  • 0 in reply to Murugavel4637
    TI__Intellectual 2840 points

    Hi Murugavel，

    Thank you so much for your feedback. Here is the information for this scenario:

    1.  VM is 12V, the max current is 350mA. customer is using 1/8 steps, PPS is 100, the resistance of the motor is 24.3±1.9；

    2.  The inductance is not tested, the current of the motor is sin wave, TrqCount is keep below 10, STALL-TH is 15.

    Best Regards

    Songzhen Guo

  • 0 in reply to Songzhen Guo
    TI__Mastermind 44525 points

    Hi Songzhen,

    Thank you for getting back to us with the additional information. The main reason the torque count is very for the given parameters and unable to detect stall successfully is the very low PPS of the application. 100 PPS for this motor with ~25Ω resistance cannot generate enough amplitude for the back EMF so the TOFF variation to calculate the torque count in the current quadrants is too low. Can the PPS of the application be increased? Unfortunately the internal stall detector cannot distinguish the stall. Can the customer slowly increase the motor speed PPS and identify a minimum speed at which internal stall detection can work?

    One potential solution for this scenario could be to use the torque count value read by the MCU which is configuring the DRV8889-Q1 via SPI to do an external comparison with a threshold value and determine stall. This will work only if customer is able to identify a threshold value that consistently will not be reached by the motor when stalled and will be above the value when the motor is not stalled. Thanks.

    Regards, Murugavel