MPC5xxxのトピックRe: MPC5748G Spread Spectrum

MPC5748G Spread Spectrum

nextsteve — Fri, 23 Jun 2017 16:04:17 GMT

Hi, I'm interested in trying out the spread spectrum feature of the MPC5748G PLL.

Wondering if there are reference register values available for STEPSIZE, STEPNO, etc. I could use to test quickly while I work through the equations.

Thanks,

Steve

Re: MPC5748G Spread Spectrum

petervlna — Mon, 26 Jun 2017 11:21:11 GMT

Hi,

We do not have reference example for frequency modulation.

You have to calculate STEPSIZE and STEPNO.

From my past experience I recommend you after calculation to use spectral analyzer for manual fine tuning.

Peter

Re: MPC5748G Spread Spectrum

nextsteve — Mon, 26 Jun 2017 16:35:13 GMT

Hi Peter, does STEPSIZE need to be non-zero?

If so, then I don't see how the calc can possibly work because with a 40MHz crystal and modulation freq=10kHz --> STEPNO=2000. N would have to be >2000 for STEPSIZE to round to anything other than 0.

What am I missing?

Thanks,

Steve

Re: MPC5748G Spread Spectrum

petervlna — Sat, 01 Jul 2017 07:43:16 GMT

Hi,

I have created example SW for you.

My STEP is 250 and modulation frequency is 20kHz.

I have verified it with spectral analyzer. You can use it as a reference.

https://community.nxp.com/docs/DOC-334867

Peter

Re: MPC5748G Spread Spectrum

nextsteve — Thu, 06 Jul 2017 22:08:45 GMT

That is awesome Peter, Thanks!