Hi There-
I'm designing an Ethernet circuit using the SP83826I and found your app note SNLA2930 which was helpful in defining the crystal for my application which must last for 20+ years. I have selected a 25MHz crystal with 18pF of load capacitance rated at 200uW drive level. The app note's section 3.9 on Crystal Drive Level details an equation and an example shown by an image below. However I don't understand how they get to a 398Ohm resistor and think I must be missing something.
If |Zc2| = | (1/(w * C2))
|Zc2| = | (1/(25000000Hz * 0.000000000016))
|Zc2|= 2500 Ohms
How is this equation used to reach a series resistance of 398 Ohms? Thanks so much!
