LMK04828: SYSREF questions

Takumi Suzuki1 said:

Q1) SYSREF cross talk

I am studying following E2E post.

http://e2e.ti.com/support/clocks/m/videos__files/666599

There are SYSREF settings, "Pulsed" (6.b) and "Request" (6.c) on the file.

Which setting is better to minimize "cross talk" against other clock lines?

And could you tell me another way to minimize if you know?

I think pulsed will be the least chance of crosstalk.  If the SYNC pin toggles a lot (which it shouldn't) or has some noise, it could couple onto VCO0, or to a lessor degree VCO1 and cause a spur.  You may consider an RC filter on SYNC pin.

Takumi Suzuki1 said:

Q2) SYSREF pulse output number

Could you advise me the output number of SYSREF pulses at a time and the interval length between each SYSREF output?

For example, 100mSec interval and over 2 pulses output...

You can think of the SYSREF pulser as gating off the requested number of pulses from the SYSREF divider.  So a pulse will come every 1/SYSREF Frequency and the duration of the pulse will be ~0.5/SYSREF Frequency.

Takumi Suzuki1 said:

Q3) Register setting of ADC amd DAC

Is it possible to set ADC and DAC registers under outputting SYSREF pulses intermittently?

Or should we output SYSREF continuously under setting the registers and after finished setting begin to output SYSREF intermittently?

Thank you for your support in advance.

I'm not sure I fully follow you here.  But yes, I think you are able to program the ADC/DAC registers, and then send the SYSREF pulses to align the LMFC between them.  Continuous SYSREF output is not necessary.

73,
Timothy