MCF8316C-Q1: Need help for speed conversion from rpm to hz

Part Number: MCF8316C-Q1

Tool/software:

As per the title, I am having difficulty defining the scale factor between RPM and DIGITAL_SPEED_CTRL when setting the speed by I2C.

I understand the number of Pole Pairs and 60 is involved, but it isn't turning out as straightforward as I thought and can't find information on where am I missing a step in the calculation.

This goes too for the SPEED_FDBK register.

  • Hi Victor,

    The formula to convert speed from RPM to Hz is:

    f =  (P * N)/60 ; where  f  is the electrical speed in Hz, P is the number of poles pairs and is the synchronous speed in RPM

    Thanks and regards,

    Sachin S

  • I understand. However, these are the values I'm seeing:

    • MAX rpm = 10,000
    • I2C Speed command % = 25
    • Measured rpm = ~2,500
    • Value in DIGITAL_SPEED_CTRL = 0x1fff = 8191 dec
    • N Poles = 6

    So by calculations, the electrical speed should be 250, but I can't see why the value in that register is 8191.

  • I have found that the DIGITAL_SPEED_CTRL field is of type DOUBLE, a fraction of the Maximum Speed