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Q&A CAN termination jumper (120 Ω → 60 Ω)

Is this a correct way to implement selectable 120 Ω / 60 Ω CAN termination using a jumper? It is weird to place both terminators on the same board. While this might fix the problem of having a...

posted 9mo ago by Lundin‭

Answer
#1: Initial revision by user avatar Lundin‭ · 2025-12-09T15:42:54Z (9 months ago)
> Is this a correct way to implement selectable 120 Ω / 60 Ω CAN termination using a jumper?

It is weird to place both terminators on the same board. While this might fix the problem of having an ideal 60Ω between CANH and CANL, it also means that there can be to protection against reflections in the other end of the bus. Which would be wrong for any bus length worth mentioning, unless this use-case scenario is just a minimal stub - then it will be OK.

Jumpers are generally horrible for rugged applications - for such, consider using some connector instead (like a 1x2 JST PH or whatever), where the mating part just shorts two pins on the wire side. 

> Any signal-integrity or EMC issues with placing the second termination through a jumper?

Nah it is not "high speed" but at most 1Mbps, so you can have any kind of connector there really.

> Is it OK that both CAN transceivers share the same choke, ESD network, and termination?

It should be fine, far as I can tell. Though I don't get why you have both ESD diodes and 2 unknown TVS both to chassis. 

More common for high integrity applications would be 2 rugged TVS to chassis close to the connector and then 2 smaller TVS like ESD diodes on the inside of the CMC towards signal ground. If you don't have high EMC requirements you can do without any of them and rely on the transceiver's built-in protection diodes.