Crystal Load Capacitance calculation incorrect

[Freshman]

I am using this device (https://ww1.microchip.com/downloads/aemDocuments/documents/UNG/ProductDocuments/DataSheets/USB251xB-xBi-Data-Sheet-DS00001692.pdf)



On page 44 of the datasheet, they have given the formula to calculate the crystal load capacitance.



I have a crystal. It's datasheet mentions that it's load capacitance is 6pF and Shunt capacitance is 3pF.

And considering 3pF for CB1 and Cxtal of 6pF (mentioned in the pin capacitance table), CS1 = 3pf + 6pf = 9pf.

​

If I substitute CS1 in the formula,

C1 = 2*(CL - Co) - CS1

CL = 6pf

Co = 5pf

 

C1 = 2*(6pf - 5pf) - 9pf

C1 = 2pf - 9pf

C1 = -7pf



I am getting negative capacitor values for the load capacitances.



Am I missing something or doing incorrectly.



So, does this crystal not support this device?

[PGPG]

I would expect PCB track capacitance being smaller than 3pF.
You write that your crystal has Shunt C = 3pF and then use 5pF in equations. Which value is correct?

[Benta]

I think you forgot to read Note 7-1 and 7-2.