Hello... Page 18 of the data sheet says to tie FB_CLK_N to GND if in CMOS mode, while page 91 of the reference manual (UG-570) says to leave FB_CLK_N unconnected in CMOS mode... which is it?
It will work either way. Some designers prefer to have all the pins terminated and tie it to GND and if your preference is to leave it open you can do that too.
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