Re: si5351a #synth

Richard G4TGJ

Hi Hans
Thanks for your comprehensive reply. How do you find time - do you ever sleep?

1. I should have checked the precise part number. It's no big deal as it still works for me and is cheap. I need the SMD practice anyway.
2. What spec are the crystals you use? I looked at Farnell, RS, Rapid, Mouser and Digi-Key. Only Digi-Key have non-SMD in stock - all the others only have them with much higher load capacitance. Even the Digi-Key crystals are 12pF which require external caps with the si5351a.
3. I followed your notes and it does work as you say. I've seen a few quirky things happen when I switch between integer and fractional modes. I think the order in which you set certain registers or reset PLLs is important.
4. I now understand why level shifters are not needed - I will remove them from my project. The outputs are open-collector as it requires wired AND so, as long as the pull-ups are to the lower voltage, it is safe. The only consideration is if the lower logic levels are OK for the higher voltage device. I have a feeling there are a very large number of unnecessary I2C level shifters in the world. As long as I am in control of the hardware design I can guarantee there are no pull-ups to 5V.


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