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SN65HVD230: SN65HVD230DR

jawher sakka
Prodigy 10 points
Part Number: SN65HVD230

Hello Texas instrument forum,

 

I found a problem with the can bus and transceiver SN65HVD230DR

Currently, I have not found the origin of this problem for that I will share with you my problem and if you have encountered this problem or you have ideas to solve it, I will be thankful to help me –

  • First of all, the can bus architecture is as follows

 

  • I work with the transceiver SN65HVD230DR under this diagram

 

  • When I made the diagnosis in case all the controllers are mounted, I found this signal curve where disturbances are superimposed with the signal

 

  • During my investigation I found that when I decreased the number of controllers from 4 down to just 2 (of course both controllers which 120-ohm resistor are mounted I didn't touch) the signal becomes smooth like the following capture

 

So my problem that I did not manage to touch the origin of this problem and I am at your disposal for any other information and of course I am open to any proposed solution to discuss.

  • 0
    TI__Mastermind 26716 points

    Jawher,

    Hopefully I understand the concern correctly: You are noticing that there are some frames where it appears the high level of CANH and/or the common-mode level of both CANH and CANL is higher than the rest of the communication?

    First, I am assuming from your post that you are exclusively using SN65HVD230 on the bus (and that there are no 5 V CAN devices attached), but correct me if I'm wrong.

    Though there are multiple frames overlaid, I think it looks to me like the entire common-mode voltage of the signal (i.e. both CANH and CANL) is shifted higher for that particular frame. Any way to know which node is transmitting for that one?

    My first suspicion is that there is significant GND shift for one of the nodes. This would cause it to have a notably different common-mode output when transmitting. The overall recessive voltage of the bus will roughly reflect the average of the entire network, but when a node is transmitting, it is the one actively driving the bus, so it's ground potential would be most prominent for that duration, as could be the case here.

    If you're not able to know for sure which node is communicating when this common-mode shift is occurring, I might recommend trying this test again but after strongly connecting the GND planes of each of the nodes to make sure they are very similar. If this causes the phenomenon to disappear, then this was likely the issue.

    If GND shift is the culprit, this is actually not that big of an issue, and likely one you won't have to worry about as long as the shift is not too serious. Differential communication protocols like CAN are built to handle GND potential differences during communication, since only the differential voltage between CANH and CANL matters when receiving. Are communication errors occurring during your testing with these frames? From what I can tell, I don't see any error frames in the images you shared.

    Hopefully some of this helps diagnose. Let me know what you're able to find out. And happy early New Year. Slight smile

    Best,

    Danny