After getting most of the peripherals figured out in the design, I started delving deeper into the datasheets for the core components. I should be doing this earlier in my design, but this is a hobby project dang-it, I think I’m allotted a handful of poor decisions.

Most of the parts had reasonably clear documentation, except for the cheap ethernet switch I selected early in the design. I’ve added the datasheet to the documents if you want to play along. Among the general lack of reference designs, I found the following…

• PLLVCC (Pin7) – What do I connect it to!!!
  The datasheet doesn’t specify where this pin should be connected. Is the rail generated internal or do I need to power it externally? Is it especially sensitive, and maybe needs some ferrites, or just a local decoupling capacitor? If you search the entire datasheet for “PLLVCC” you’ll find two instances. One is the pin diagram, the other is the pin description, “Power of PLL circuit”.
  Resolution – For the first prototype I’ll add a jumper to power PLLVCC either from 3V3, 1V0, or leave floating w/ decoupling.

• VREG_LDO (Pin41) – Min Capacitance?
  I’d really like it if the datasheet gave any sort of comment regarding output capacitance for the internally generated regulator. What is required for stability at least, or even a comment saying there IS no minimum….
  Resolution – Adding 0603 1uF Cout. Larger package allows for tweaks later if needed.

• EEPROM – What Address?
  This one is pretty depressing, and would have been exceptionally easy to add correct. The device uses an external I2C EEPROM that can store configs that are loaded at startup. However, the address of this EEPROM isn’t specified.
  Resolution – Select EEPROM with configurable address. Sniff bus when prototype board arrives.

• Magnetics Ect 
  This might be caused by my inexperience in networking related designs, but I’d really like to see some baseic design recommendations for the magnetics. My understanding is that the topology of the PHY can have several downstream affects for the termination / center tap on the transformer. Lacking this info, I’ll design in what seems most widely used.