Electronic – CAN bus split termination impedance – no 60 ohm resistors


Typical CAN Bus termination involves a 120Ω resistor between CANH and CAHL. To go further than this, I've read that the 120Ω resistance can be split into two 60 ohm resistors with a capacitor in between to ground (Typically 4.7uF). This has the benefit of creating a low-pass filter for the common-mode noise on the network.

Because 60Ω is not a standard resistor value, is there anything wrong with using 60.4Ω resistors or two 30Ω resistors in series? Or is there another method to accomplish this.

Best Answer

You'll be lucky if the average differential characteristic impedance of your transmission line is within +/- 10% of the nominal 120 ohms; small inaccuracies in the termination network will not have a significant effect. 2x 60.4 ohms will be fine. Even 2x 62 ohms (E24) would be fine. Better to go slightly higher than nominal rather than sightly lower, since the receiver IC will have a couple of kiloohms of effective input differential impedance which will act in parallel with your termination network, lowering the combined impedance seen by the line.