Do we need to control impedance of CAN BUS ?

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pcbgogo_dph
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Do we need to control impedance of CAN BUS ?

#1 Post by pcbgogo_dph » 22 Aug 2018, 22:06

Hi All,

My hardware design is most similar to imx Open Rex design development board and I have included CAN BUS port to my custom design.

In my memory layout I controlled impedance as 100 Ohms for differential pair and 50 Ohms for single ended signals.

Do we need to control impedance of the CAN BUS traces ? If yes what is the impedance value ? Can CAN BUS signal traces affect to memory layout if I didn't control CAN BUS trace impedance ?

Regards,
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Arson
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Re: Do we need to control impedance of CAN BUS ?

#2 Post by Arson » 13 Sep 2018, 04:49

60 Ohm impedance, 120 Ohm terminator.
Sometimes a little brain damage can help.

Retika
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Re: Do we need to control impedance of CAN BUS ?

#3 Post by Retika » 04 Feb 2019, 07:26

For high-speed/FD CAN, both ends of the pair of signal wires (CAN_H and CAN_L) must be terminated. This is because communication flows both ways on the CAN bus. CAN_L is pin 2 and CAN_H is pin 7 on the standard 9-pin D-SUB connector. The termination resistors on a cable should match the nominal impedance of the cable. ISO 11898 requires a cable with a nominal impedance of 120 Ω; therefore, you should use 120 Ω resistors for termination. If you place multiple devices along the cable, only the devices on the ends of the cable need termination resistors. Figure 1 shows an example of how to terminate a high-speed network.
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"Do we need to control the impedance of the CAN BUS traces? If yes what is the impedance value ?"
- You may want to. See the note above (we used 100OHM for the short tracks in OpenRex)

"Can CAN BUS signal traces affect to memory layout if I didn't control CAN BUS trace impedance ?"
- no

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