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DRV10987: About the maximum rotation speed with driving 3phase brushless motor

user5945607
Prodigy 170 points
Part Number: DRV10987
Other Parts Discussed in Thread: DRV10983, DRV10975

Hello,I found DRV10987 can drive 3phase brushless motor at a constant speed with easy way such as PWM,I2C and Analog input.

1. Could you tell me whether the maximum rotation speed  is difference according to the control way or not?

2.when I choose the I2C for speed control,I need to set the register of motorspeed1:0x11 and motorspeed2:0x12 .

  and We can set 0x00～0xFF in the registers.

  if both motorspeed1 and  motorspeed2 are 0xFF,motorspeed is calculated as below:

   65536/10=6553.6Hz    →6553.6Hz＊60sec=393216rpm

　I　think it is not possible to drive the motor at 393216rpm because of hardware limitations.

   Could you tell me what is the maximum rotation speed with I2C control ?

3.when I choose the PWM for speed control,I need to set the maximum speed with the register of SpeedCtrl1:0x00 and SpeedCtrl:0x01.

   and We can set 0x00～0x1FF in the registers. What is the unit of the number?

   Could you tell me how can I calculate the motor rotation speed?

  • 0
    TI__Expert 6065 points
    Just to clarify, the DRV10987 doesn't by itself guarantee a constant speed. The speed cmd that we enter just decides what duty cycle % we are driving the motor. Usually the motor will spin at a constant speed at a given duty cycle, but if the motor has variable load torque, speed can changed

    1) The maximum rotation speed STAYS THE SAME regardless of whether the speed input is set to PWM, I2C or Analog input.
    2) The "motorspeed1" and "motorspeed2" registers at 0x11 and 0x12 are in DRV10983 and DRV10975, not in DRV10987. In DRV10987, the equivalent registers to read motor speed is motorspeed at 0x01. Please refer to section "8.4.12.2 Motor-Speed Readback" to see how speed in Hz is calculated.
    3) This is in DRV10983 datasheet, not DRV10987. Please confirm which device you are using.

    Sincerely,
    Sanmesh U.
  • 0 in reply to Sanmesh Udhayakumar
    Prodigy 170 points

    Thank you for your reply.

    I'm sorry for my misunderstanding. Can I ask below questions again?

    if my understanding is correct,We can change the motor rotation speed with the register of SpeedCtrl:0x30 by 512 steps,

    and We can monitor the motor rotation speed with  the register of motorspeed:0x01.

    is it correct?

    Thanks and best regards.