Choosing a MOSFET for carrying a fast analog signal

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Hi there - I'd like to pass ISO 11898 (CAN) signals through an N-FET. I'm very comfortable using MOSFETs for power switching. This is the first time that I've wanted to pass a fairly quick signal through one though.

Can anybody tell me what I should be looking for here? What specs are important, and which aren't? I guess the main ones that I care about are the Rdson, and the various capacitances. I've yet to find a good diagram explaining what all the different capacitances are, unfortunately.

Thanks so much for your help!

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I gather you want to route the can bus? Could you not use something like the old 4066 bilateral switches? I dare say the currents involved are reasonably small.

Or are you wanting the mosfet to drive the Can bus rather than a Can specific transciever? Rds on shouldn't be a major issue unless you really want to pull some current. Something like a 2n7002 or bs170/mmbf170 should give you enough speed and not require anything other than a ttl compatible output to drive it.

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Kartman wrote:
I gather you want to route the can bus? Could you not use something like the old 4066 bilateral switches? I dare say the currents involved are reasonably small.

Or are you wanting the mosfet to drive the Can bus rather than a Can specific transciever? Rds on shouldn't be a major issue unless you really want to pull some current. Something like a 2n7002 or bs170/mmbf170 should give you enough speed and not require anything other than a ttl compatible output to drive it.


I actually want to use the FETs to enable/disable termination. The number/position of nodes on my CAN bus is going to be changing pretty regularly, so in order to avoid having to move around the termination manually, I want it software controlled.

To make things complicated (and the reason I can't use any analog switches that I know of) - there will be times when the bus is in use, but some nodes are not powered. In those cases there are also times when the CANH line could be held at about 36V. All of the analog switches that I have seen cannot handle this.

So I guess the answer is that I'm looking to route the CAN bus. I'm not looking to drive or amplify anything - I just want a switch.