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Custom CAN-FD PCB, what to watch out for ?
1329 1 Mar 11.2020, 21:34:20

I'm designing a PCB which will communicate with a vehicle through CAN-FD at up to 2 Mbit/s.
The connection to the vehicle is made though ordinary twisted-paid CAN wire (around 2m) to a Mini Universal MATE-N-LOK connector on the board.
From there, it's approximately 15mm of 8 mil trace to the MCP2558FD CAN-FD tranciever, and approx. 6mm of trace to the termination resistors and decoupling capacitors.
The Teensy 4.0 I use for controlling this has an integrated CAN controller, but it's only available through SMD pads on the bottom side of the PCB.
Therefore, I soldered a short wire to those pads (~20-30mm) and plan on then soldering the wires to a hole in the PCB near the CAN transceiver (around 12mm of trace for the TX line, 5mm of trace for the RX line).
Do I need to consider anything special here? It's my first "high-speed" signal application.
Does the length / impedance of the CAN-FD traces on the board (between transceiver / connector) matter? Would the MATE-N-LOK connector be an issue? Is 2m of "external" CAN wire too much for signal quality? For now, the Teensy will only listen to messages on the bus, without receiving anything (using the MCP2558FD's "silent" mode), but I'd like to be able to send data in the future.
Is it a reasonable idea to transmit the 2 MBit/s UART (between Teensy / transceiver) through external wires? Other options (pogo pins (low availability), castellated holes (SMD components on the bottom side of the Teensy), SMD headers (different height compared to THT headers)) seemed suboptimal as well.
Could I route other signals (in this case, current signals up to around 30 mA) on the other side of the PCB, or must I retain an uninterrupted ground plane there?

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Mar 18.2020, 14:26:20

The CAN bus is designed to be incredibly robust and be able to handle large amounts of crap being thrown its way. You'd be surprised how bad things need to get in order for data to be corrupted on the bus.

If you can't properly terminate the wire you're connecting to the vehicle, it would be better to have your CAN-USB interface right next to that connector and just run a longer USB cable to your computer.

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