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I'm using a line that is multiplexed to be used with digital 0-5V, 0-7V and CAN. I don't know very much about CAN swing voltages, so, I have some doubts:

  1. Need CAN protection to be bidirectional? If I use a unidirectional protection will interfere in the communication ?

I'm affraid that during a negative peak, using a bidirectional TVS diode, the voltage at the pin of the device will be negative and it can damage the devices that are not CAN, the CAN transceiver can tolerate negative voltage, but the others don't.

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CAN uses 2.5V +/- 1V positive levels on both CANH and CANL. It does not have negative voltages like RS-485/RS-232. So there is no point in using bidirectional TVS.

Most CAN transceivers are very rugged and can handle large voltage differencies, so depending on application and transceiver picked, TVS may not be necessary. The most modern ones like for example MCP2562FD can handle +/-58V and got built-in TVS.

In this case given the 0-7V option, a TVS somewhere around 9-12V might be suitable.

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  • \$\begingroup\$ Ok, I understood. But, I still can't understand one point: the majority of time, I see the use of bidirectional TVS, even for 0-5V signal. If a negative peak happens with a bidirectional diode, this dipositive would be damaged, no ? \$\endgroup\$
    – Daniel
    Mar 29, 2021 at 14:05
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    \$\begingroup\$ @Daniel It depends on the type of signal and the application. This seems like a decent app note on the topic: mouser.com/pdfdocs/AND8424-D.PDF \$\endgroup\$
    – Lundin
    Mar 29, 2021 at 14:09
  • \$\begingroup\$ Yes, I knew this app. This was one of my reasons to want to choose unidirectional TVS. But, In in a training video of Texas they use a bidirectional TVS to a USB lines and power. As I know, USB power can only be positive, and in the video, at ~2min, they say that I can use whatever polarity of TVS: training.ti.com/… \$\endgroup\$
    – Daniel
    Mar 29, 2021 at 14:23
  • \$\begingroup\$ So, or I did not undertood TVS correctly, or the explanation in the video is wrong. Probably I did not understand it correctly... \$\endgroup\$
    – Daniel
    Mar 29, 2021 at 14:25
  • \$\begingroup\$ @Daniel I rarely ever use USB so I don't know. \$\endgroup\$
    – Lundin
    Mar 29, 2021 at 14:32

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