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

Victor Oh

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.

4 days ago

0 Sachin S 4 days ago

TI__Intellectual 2071 points

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 N is the synchronous speed in RPM

Thanks and regards,

Sachin S

0 Victor Oh 3 days ago in reply to Sachin S

Prodigy 10 points

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.

+1 Victor Oh 3 days ago

Prodigy 10 points

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

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