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Crystal capacitance ADE 7878A

Category: Hardware
Product Number: ADE7878A

I'm currently working in the design of an ADE7878A circuit schematic. I've been using the datasheet and EVM user guide for reference.

I have an issue, because in the datasheet (www.analog.com/.../ade7854a_7858a_7868a_7878a.pdf), page 76, it is highly recommended to use the same crystal that is used in the EVM VM6-1D11C12-TR-16.384MHZ, with ESR 20 Ω; load capacitance 12 pF. I'm worried about the component availability, I don't match the same crystal specifications. Also, it says that lower ESR and load capacitance values are preferable.

So, the datasheet also gives you some equations to calculate the capacitors you have to add to reach the 24 pF at each clock pin (CLKIN CLKOUT), and using a crystal with 12pF of load capacitance, the values of the ceramic capacitors added (besides the parasitic capacitance) are about 22 pF each one.

In conclusion I have the following questions:

a) Is the total capacitance at each clock pin THAT critic for the design? Is there any suggestion in the case i don't find the SAME crystal named at the datasheet?

b) Supposing I don't have any other option than using a crystal with the SAME frequency, but 20 pF of load capacitance and 40 Ω ESR (https://datasheet.lcsc.com/lcsc/2103291205_Yangxing-Tech-X49SM16384MSD2SC_C70701.pdf). What would the correct values for the ceramic capacitors to be added at each clock pin? Following the equations, I get that I'd have to place 38 pF capacitors, but it doesn't satisfy the total capacitance equation.

Nothing more to add, I hope you can read this and give me a help to outcome my problem. Thank you so much in advance,



reference correction
[edited by: LucasDS at 6:08 PM (GMT -4) on 26 Oct 2022]