Problem with Xtal Pins

Question

Hi, I’ve designed a board with TWO W5300 on it, I used a 25MHz crystal oscillator for each.( CRYSTAL 25.0MHZ 18PF 20ppm 100 ohm, SMD , MANF PN:ABLS-25.000MHZ-B2F-T) when I started the hardware test I had no Clock on Xtal Pins, I tried changing Xtal Capacitors by values of 13PF,18PF, 22PF, 33PF, 46PF and 56PF Now one of them oscillates with 46PF capacitor installed but the other has no oscillation. I tried changing that Xtal with NTK 25MHz Xtal but also have Problem with it, Please help me to rectify this problem.

peter · Answer

It seems like load-capacitance matching problem. Load capacitance matching is affected by versatile factors. (pcb routing status, copper thickness(oz)……) If 18Pf of CL value, theoretically, I recommend 39pF external capacitors. Or, 1.8V level oscillator can be used.

EEProjs · Answer

Thanks for reply, PCB is designed on 50 Ohm tracks like below: Track width= 4.5 mil, copper thickness: 3 mil dielectric constant: 4.3 is 50 ohm impedance matching OK for Xtal Pins?