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MCF8316A: -101

yao eddie
Prodigy 40 points
Part Number: MCF8316A 
Hello,

On page 96, in  CLOSED_LOOP4 Register, under Register Field Description section, it says:

"MAX_SPEED:  14-bit value for setting maximum value of speed in electrical Hz Maximum motor electrical speed (Hz): {MOTOR_SPEED/6} For example: if MOTOR_SPEED is 0x2710, then maximum motor speed (Hz) = 10000(0x2710)/6 = 1666 Hz."

In the description, I'm not sure if MOTOR_SPEED is another Register Field, or perhaps MOTOR_SPEED  is a typo of MAX_SPEED, as I cannot find MOTOR_SPEED as a register valve in the datasheet.

also, I quite confuse about these and hope you can try your best to make me clear.

1. There is notvany register to set the pole pairs, how MCF8316A use the MAX_SPEED to calculate the motor electrical speed?
2. why use 6? for example, if the MAX speed of the fan is 40000 RPM, and the pole pairs is 1, how can I set the MAX_SPEED？


Best wishes
  • 0
    TI__Expert 7865 points

    Hi Yao,

    The MOTOR_SPEED is a typo in the register description in the datasheet. It should be MAX_SPEED instead of MOTOR_SPEED:

    14-bit value for setting maximum value of speed in electrical Hz Maximum motor electrical speed (Hz): {MAX_SPEED/6} For example: if MAX_SPEED is 0x2710, then maximum motor speed (Hz) = 10000(0x2710)/6 = 1666 Hz

    1. The device register accepts motor electrical speed in Hz. Pole pairs is only needed to calculate the electrical speed in Hz if the user only knows the max speed in RPM mechanical speed. The equation for conversion between Hz and RPM is:
    2. 6 is simply an arbitrary scaling factor that the device algorithm implemented in order to represent the supported maximum speed range in 14-bit. It converts between the register's 14-bit hexadecimal value (unitless) into motor electrical speed in Hz.

      If your mechanical max speed is 4000 RPM and pole-pairs is 1, then using the equation above:
      4000 * 1 / 60 = 66.667 Hz

      To enter this in the register, use the equation in the register description:
      66.667 * 6 = 400 = 0x190

      So you would enter 0x190 into the register to set the max speed to 4000 RPM.

    Regards,
    Eric C.

  • 0 in reply to Eric Chen
    Prodigy 40 points

    Hi Eric,

    I got it , thank you for your kind reply.

    Regards,

    eddie

  • 0 in reply to yao eddie
    TI__Expert 7865 points

    Hi Eddie,

    No problem, I will close this thread.

    Regards,
    Eric C.