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I have my CAN configuration as shown in the below drawing(automotive application),enter image description here the uC that I’m using has both the CAN controller and the physical layer transceiver built-in so I don’t need a transceiver outside the uC. I have a doubt regarding the common mode choke, I have read that the common mode choke will degrade the signal, below is the link to the question where this is stated  Are Common Mode Choke Coils needed on USB? 1) I would like to understand how the signal degradation can be evaluated, I'm trying to select a common mode choke for CAN network with 500kbps baud rate and want to know things I have to consider while choosing a common mode choke. I understand that there will be some delay in the signal, but is there any way to theoretically calculate this time by simulation ? Or is testing required ?

2) Below is the link to an application note by TI, titled “Common Mode Chokes in CAN Networks: Source of Unexpected Transients”, which states that “extremely high transient voltages that maybe generated by the inductive flyback during a short circuit of a CAN bus line to a dc voltage.” Should I test my circuit during short circuit conditions to see the voltage that the uC pins will see. http://www.ti.com/lit/an/slla271/slla271.pdf

3) Apart from EMC tests, is there any other electrical test that I can conduct to look at the effects that the common mode choke has on my circuitry.

4) I also want to see the effect the capacitors C2, C3 and diode D1 has on the circuitry during ESD pulses. Is there a ESD pulse model available in LTspice and is it possible to simulate and see the results in Ltspice ? Is it feasible to do this ?

Nidhi
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  • The best part meets the best specs for Ingress susceptibility, egress , Bus current, cost and short cct protection – Tony Stewart EE75 Mar 10 '20 at 01:08
  • I'd just pick a part designed specifically for CAN. Murata has several of these, for example. – Lundin Mar 10 '20 at 07:53
  • @TonyStewartSunnyskyguyEE75 are they any tests that I can conduct excluding EMC tests. Would it make sense to conduct the short circuit test like in http://www.ti.com/lit/an/slla271/slla271.pdf . – Nidhi Mar 10 '20 at 08:56
  • @TonyStewartSunnyskyguyEE75 are they any tests that I can conduct excluding EMC tests. Would it make sense to conduct the short circuit test like in http://www.ti.com/lit/an/slla271/slla271.pdf and compare the levels of transients for two common mode chokes and select the part with lower levels of transient voltage ? – Nidhi Mar 10 '20 at 09:02
  • Yes there are tests for each specified criteria you need. But where are your specs? – Tony Stewart EE75 Mar 10 '20 at 13:48
  • @TonyStewartSunnyskyguyEE75 Ok actually we had ACT45B-101-2P-TL002 common mode choke and now considering VFB4532-101V, the main parameter differences that I see is in the inductance tolerance.ACT45B->-30% / +50% and VFB4532-101V -> ±40% and stray inductance was 400nH in the ACT45B part compared to 200nH in VFB4532 part, and slight differences in the impedance vs freq characteristics. I have both the parts available with me, can you please suggest some tests which I can conduct and decide on using the VFB4532 part in place of ACT45B part. – Nidhi Mar 10 '20 at 15:48
  • Emission tests are good for ingress /egress CMRR but L/R helps define Tau and useful spectrum estimate. Depends on what you need. – Tony Stewart EE75 Mar 10 '20 at 16:41
  • @TonyStewartSunnyskyguyEE75 I need to understand how my CAN signals are being degraded with respect to time, i want to understand the delay that the choke could be adding to the signal and also does it make sense to conduct the short circuit test as described in ti.com/lit/an/slla271/slla271.pdf titled “Common Mode Chokes in CAN Networks: Source of Unexpected Transients” – Nidhi Mar 10 '20 at 16:57
  • @Nidhi group delay of an all pass filter theory and BW are related to emission transfer function, but you need to worry about signal integrity, emissions , crosstalk from impulse noise on data errors then short circuit impulse protection – Tony Stewart EE75 Mar 10 '20 at 17:06
  • @TonyStewartSunnyskyguyEE75 Could you please give me a few starting hints on how to go about it, I have both the choke parts with me, any suggestions on tests that I can conduct ? – Nidhi Mar 10 '20 at 22:16
  • Learn to understand the requirements 1st then define specs, then the tests are easy to define for each category. – Tony Stewart EE75 Mar 10 '20 at 22:19

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