As I've seen in LM15851EVM, SYNC~ input of the LM15851 is directly driven by TSW14J56's FPGA diff output. Is that output is configured as an LVDS output?
If so, it doesn't meet common mode voltage requirements for the LM15851 SYNC~ input specified in the datasheet, as LVDS driver has common mode voltage around 1.2V and required range is 0.64V to 1.1V (Recommended Operating Conditions table, p.10).
Have I missed something? Can you give some comments?
Best regards, Vic.