# Crystal reference and capacitors for w5500

I'm selecting the caps for the crystal oscillator of the wiznet W5500. The standard Load Capacitance for 25Mhz crystals is 18pF. I found out that the hardware guideline claims for a Load Capacitance crystal (CL) of 18pF, and taking into accout the formula to select CL0 and CL1, and assuming Stray Capacitance (CS) of 4pF...

CL1 = CL0 = 2 (CL - CS) = 2 (18 - 4) = 28 pF

If you take a low CS of 3pf, it gives 30 pF, and if takes a high value of CS like 5pf, it takes 26pF.

Why, then, in all reference schematics I found (including wiznet schematic reference), CL0 and CL1 are 18pF ???

• You have a point. Wiznet's crystal selection guide for the W5100S (a closely related part) mentions typical values for CS in the range 5-7pF. Even assuming CS = 7pF, you get CL0 = CL1 = 22pF for CL = 18pF. Suggest you post this question to the appropriate Wiznet forum. See also this question - clearly the crystal spec is important for reliable operation of these parts. – amb Aug 11 '18 at 11:48

Double-check the BOM. I see a lot of crystals with <10pF CL, especially in small SMD packages. The 18pF CL0/1 seem about right for those when you include trace and pin capacitances.