I am trying to change the CAN cables alone to Cat 6 cables (which has 100 ohm characteristic impedance). The existing cable has 120 ohm impedance. By making this change to Cat 6 cables, I am trying to find out if there would be any issue with CAN signal integrity because the PCB transceivers remain the same with 120 ohm terminations in them.
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2\$\begingroup\$ What is the (total) length of the cable(s)? What is the bit rate on the CAN bus? \$\endgroup\$– Peter MortensenCommented Mar 20, 2018 at 16:33
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That’s not that bad a mismatch. Unless you are already at an extremely marginal situation, it shouldn’t have any impact.
To see that via theory, when the bit wave reaches a terminator, I and V are balanced around 100 ohms, a 1:100 ratio. Suddenly the terminator is forcing a 1:120 ratio and that mismatch will cause reflections of the wave. That’s a mismatch by about 1/6th, so if you’ve got 30% margin you’re still good.
Empirically, if you do have a problem you can add 600 ohm resistors to the two (and only two!) existing terminators to make them effectively 100ohms.
answered Mar 20, 2018 at 21:09