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I have a PCBA where the connector for the CAN bus is about 40 mm away from the MCU. The MCU and connector positions are fixed but I am free in placing the CAN transceiver.

I haven't worked with CAN bus before. I believe the intention is to use it at full speed (1 Mbit/sec).

  1. Are CANH and CANL more important to lay out carefully or the Tx and RX from the transceiver to the MCU? I can place the transceiver close to the MCU or close to the connector.

  2. Do I need to ensure the CANH and CANL are length-matched?

  3. Are there any particular precautions to take for TX and RX? Such as the use of vias or distance?

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  • \$\begingroup\$ 40mm is almost nothing. However, to get down to tje details, the answer could depend on what is the purpose of this device. Is the CAN bus supposed to be terminated on the board, or pass/loop through it? Or connected to the bus via a stub? \$\endgroup\$
    – Justme
    Commented Apr 22, 2021 at 16:33
  • \$\begingroup\$ Note EMI improvement 60R<>C<>60R termination for certain end points. ww1.microchip.com/downloads/en/Appnotes/00228a.pdf \$\endgroup\$ Commented Apr 22, 2021 at 16:49
  • \$\begingroup\$ It's undecided whether it terminates on the board. I've added a 120 R res on the CanH and CanL with a jumper header in case it needs to be terminated. \$\endgroup\$
    – Hasman404
    Commented Apr 22, 2021 at 17:05
  • \$\begingroup\$ The main concern here should be picking the right transceiver. With the advent of CAN FD, all silicon vendors have released new parts that can cover both classic CAN and CAN FD. You'll want to pick one of these new parts since the older once risk getting phased out. They are mostly compatible, but pin 5 and 8 (assuming classic SO8) have specialized functionality which isn't standardized. \$\endgroup\$
    – Lundin
    Commented Apr 23, 2021 at 10:18

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I've added a 120 R res on the CanH and CanL with a jumper header in case it needs to be terminated

Do you realize that this jumper will probably affect the signal more than 30mm traces? I am saying 30mm because you'd need about 10mm for transceiver in between your two points.

Anyway, at this distance you should be fine no matter what you do. Having said that,

  1. I would recommend placing transceiver next to connector;
  2. If you do (1) then matching traces becomes pointless;
  3. At 1Mbit you have relative freedom of routing TX and RX. Of course VIAs should be avoided, but that is true for any design, not your case in particular.
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