CAN Bus: EMI capacitor values

pbain — Fri, 24 May 2019 02:27:20 GMT

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

Re: CAN Bus: EMI capacitor values

igorpadykov — Tue, 28 May 2019 00:08:31 GMT

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.pdf

Best regards
igor
-----------------------------------------------------------------------------------------------------------------------
Note: If this post answers your question, please click the Correct Answer button. Thank you!
-----------------------------------------------------------------------------------------------------------------------

topic Re: CAN Bus: EMI capacitor values in i.MX Processors

CAN Bus: EMI capacitor values

Re: CAN Bus: EMI capacitor values