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I'm designing a board with LAN8720 and LPC1768.
LPC's ADC and LAN's magnetics connections require analog 3.3V power.
Should I separate these two analog power planes with a ferrite as I separate it from digital 3.3V power plane? Or is it OK to use only one analog 3.3V power plane?
I edited this message and added below picture. Ethernet PHY(LAN8720) to magnetics connection and LPC1768 ADC is using 3.3V analog power. Is it better to keep them separate as I draw in the picture?
Form what I read: "The digital ground pins (GND), the analog ground pins (AVSS), and the GND_CORE pins on the LAN8720 QFN are all connected internally to the exposed die paddle ground. "
So use a separate analog ground for your ADC as you mentioned above. Maybe it will work if both share the same ground plane, but it's easier to omit a ferrite if you don't need it than add one in if you do.
I'd do it like this: -
Note that I've shown 0V (ground) and 3.3V power going straight to the noisy object (the digital block) and from where the connections hit this block I would tee-off to separate power and ground planes for each of the ethernet block and analogue block.
Reason: I don't like digital currents in a ground plane getting any further than they need to and this means minimizing digital ground currents (or 3V3 currents) from upsetting the ethernet and ADC sections.
