Quartz crystal ascillator and capacity load

[schneiderj]

Hello,

I have trouble with the following crystal : https://www.farnell.com/datasheets/97450.pdf. This datasheet give a capacity load of 18 pF, and as first trial I would like to use 2 capacitor with this value. But I read a document on this page : **broken link removed** and from here I think that my understanding is wrong.

It seams that this 18 pF is the value of the equivalent of C14, C15 and C16 capacitor in the following circuit :

**broken link removed**
and as I don't want to use C16, I will have 1/CapaLoad = 1/C14 + 1/C15.

Is that correct ?
Thanks for your help,
Jean-Marie

 

[Sceadwian]

I have never seen a circuit with a capacitor connected like that intentionally. I think C16 is just a parasitic load, it's not an intentional capacitance, you can safely ignore it unless your crystal is a large distance away or there is some other reason for high capacitive coupling between the two leads.

 

[schneiderj]

I have never seen a circuit with a capacitor connected like that intentionally. I think C16 is just a parasitic load, it's not an intentional capacitance, you can safely ignore it unless your crystal is a large distance away or there is some other reason for high capacitive coupling between the two leads.

Thanks for your comments.
But what is the correct value for C14 and C15 for a capacity load of 18 pF ?
If C14 and C15 have a value of 33 pF fine ?

Jean-Marie

 

[schneiderj]

A little up...

 

[rogs]

I found the information on page two of this datasheet: http://www.datasheetcatalog.org/datasheet/CML/mXyyzquy.pdf
quite useful in calculating crystal load capacitance.