A few years ago I had to design a board that uses the NXP LPC1769 MCU and had Ethernet connectivity. I was in need of a PHY chip and the LAN8720 was choosen.
During design however, I noticed that NXP in their development boards use an inverting buffer on the REFCLOCK signal (see here, U9). I searched the datasheet, but I couldn't really understand the reason for this inverter. Finally I decided to follow their advice and also use the inverter. The board worked perfectly, as many more following designs did.
Now we are migrating to the STM32F427 MCU, and again I need Ethernet connectivity. I plan to use again the LAN8720 PHY, but I am confused about whether I should invert the REFCLOCK signal again.
Since I didn't understand why it was needed in the first case, I am not sure what to look for now to ensure whether it is needed or not.
Why this inverter was used? Where one can find information on the datasheet about this? And most importantly how can I know whether I need it on the new design?
Note: Space is at a premium for my new design, so eliminating even such a small part will be beneficial. I wouldn't really like to add it to the design just for a trial-and-error approach, only to find out it needs bypassing...