CAN Bus: EMI capacitor values

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CAN Bus: EMI capacitor values

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pbain
Contributor III

Hi all,
Using 3 of the TJA1042 CAN transceivers for a new design in conjunction with a i.MX8. The project managers have requested that the 3 channels be capable of 1Mbps each, with a default of 250kbps. I have all the circuits designed except for the EMI capacitor values. These are 2 matched capacitors in the pF range between CANH and GND, and CANL and GND.
From what I can find, the value of these will change depending on the bps. Given they want the potential full 1Mbps available for use, I assume I use the value suitable for this. I am struggling to find documentation on how to calculate the values though. I think it is around 35pF from a couple examples I have found. The TVS I am using has a Cd of 25-30pF so if this is the case, I may not need the capacitors at all.
Any links to a resource which shows how to calculate these values based on the kbps?
Thanks

Peter

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igorpadykov
NXP TechSupport
NXP TechSupport

Hi Peter

for considerations regarding capacitors selection one can look at AH1014  Fig.45

https://www.nxp.com/docs/en/supporting-information/AH1014_v1_4_Application_Hints_TJA1042_43_48_51.pd... 

Best regards
igor
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