• State TI Thinks Resolved
  • Locked Locked
  • Replies 4 replies
  • Answers 1 answer
  • Subscribers 30 subscribers
  • Views 394 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

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.

DRV10964: Keeping the motor spinning

Jens van Zon
Prodigy 10 points
Part Number: DRV10964

Hello TI support Team,

i have an PCB-BLDC motor, 6coils und a flat disk with 8 magnets. To drive this motor i chose an DRV10964.

With 2 coils in series it has Phase to Phase resitor about 20Ohm, an inductance about 48uH and a Kt about 2,4 (125kHz / Vss = 600mV). Vcc ist 5V

I test different config settings und let the duty cycle increase.

It always turns out the same.

The disk aligns, it is accelerated nicely and the motor spin out until stop.

In the scope i can see the individual phases very clearly.

Align, open loop acceleration, HI-Z, closed loop, spin out.

I`m wondering why the driver stops and what lock kicks in to stop the motor.

Can you help me figure this out so I can improve the design?

Thank you.

  • 0
    TI__Genius 16325 points

    Hi Jens Van Zon,

    Can you explain Kt how you are measuring? Is it 2.4mV? or what is the max speed of motor?

    Looks like it is in self-configured start. But, we will verify once again by programming both Kt t[7:0] and Rm[7:0] and start the motor.

    Open loop to close loop configuration has to be set appropriately, please refer to the EVM user guide DRV10964 Evaluation Module User's Guide (Rev. A) 

    You can try different hand of threshold values, refer to Table 6 and Table 7 for the hand off selection guide.

    Thanks and Best Regards,

    Venkatadri S

  • 0 in reply to Venkatadri Shantaram84961
    Prodigy 10 points

    Hi Venkatadri, Happy New Year

    I haven't had much time lately.

    It could be that I measured the 2.4mV against GND.
    I made a new measurement of the Kt value.
    I measured one phase (2 coils in series). I powered the rotor with a small motor. I get a sine wave at 500Hz and has a peak to peak value of 2.28V.

    Kt = (2280mV/500Hz) = 4,56mVs or Kt = (2280mV/500Hz)/1,41 = 3,23Vs.
    I'm not sure if I still have to divide by root 2. However, the value is in any case well over 1mV.

    I can't say what the maximum speed of the engine is. But I would like to achieve a speed of around 3000 rpm.

    Am I correct that at 500Hz and 4 pairs of poles I have to have a speed of 7500rpm?
    n = (500Hz / 4pp) *60 = 7500rpm

    The sentence: "Looks like it is in self-configured start. But, we will verify once again by programming both Kt t[7:0] and Rm[7:0] and start the motor." I do not completely understand this. How can I program Kt and Rm myself?

    I haven't tried all of the different hand-of-thresholds yet, so I still have to add some hardware.
    Which PWM setting should I use to set the hand-of-threshold? At the moment I have the minimum of 10%.

    Thanks and Best Regards

    Jens van zon

  • 0 in reply to Jens van Zon
    TI__Mastermind 23731 points

    Hi Jens Van Zon,

    Thank you for the additional information! Today was a holiday for TI, but we will aim to provide a response by the end of the week.

    Regards,

    Anthony Lodi

  • 0 in reply to Jens van Zon
    TI__Genius 16325 points

    Hi Jens van zon,

    DRV10964 measures Rm and Kt during startup and we cannot program this. Please ignore my explanation about programming Kt/Rm as this is not applicable for this device.

    Hand off speed is determined through experiment. The higher speed motors will have lower Kt and hence we have to drive to higher speed to get good BEMF for close loop to reliably switch and control further. Therefore, try increasing the Hand off in steps and fix to the value at a point where we see stable hand off every time.

    Thanks and Best Regards,

    Venkatadri S