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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.

TonyM
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dos584
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    Should be fine. You could also use two 120 ohm resistors in parallel. But I would just use the 60.4 Ohm resistor. That's well under 1% accurate. Don't forget your non-standard 60 Ohm resistor has a tolerance too, as does your cable (which is going to be far looser than 1%) – DKNguyen Oct 22 '19 at 03:58
  • think about this .... what is the value range of a 60.4Ω 5% resistor? – jsotola Oct 22 '19 at 04:02
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    Can you draw a quick schematic? Just to make sure everyone understands what you are proposing? You can edit your question then add the schematic using the built-in schematic entry tool (look for a button with schematic symbols on it). Short answer is that if 60 works, 60.4 would be fine also. – user57037 Oct 22 '19 at 04:07
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    @mkeith everyone has provided meaningful comments and i'll be accepting pericynthion's answer. I assumed as much but just wanted to be sure because i couldn't find an answer to this here or elsewhere. Thanks! – dos584 Oct 22 '19 at 04:32
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    I just wanted to make sure you were maintaining a differential impedance of 120 Ohms. Wasn't 100% clear on how you wanted to split the resistor. It is no big deal. Glad you got your answer. – user57037 Oct 22 '19 at 04:49
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    @jsotola There's not really any reason to use 5% resistors nowadays though. 1% is just as cheap or cheaper. – Lundin Oct 22 '19 at 12:40

1 Answers1

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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.

pericynthion
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