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TCAN332: CAN BUS dropped packets troubleshooting

Gideon Kanikevich
Prodigy 40 points
Part Number: TCAN332

Tool/software:

I am trying to diagnose and resolve some frequent dropped packets on our CAN BUS. I have designed the hardware while our software engineer has designed the firmware.

All our modules utilise the TCAN334DR CAN transceiver and being changed over to TCAN332DR in the next iteration of our PCB spin. All our modules utilise an  ESP32-D0WD-V3 to interface with the CAN transceiver.

The pretty simple CAN design on each module can be seen below.

The first module on the bus has the termination components (R6, R7, C37) fitted. All other modules have those components not fitted. The bus is terminated with a custom split 60R termination plug.

Here is a screenshot of the scope measuring CAN_H on CH1 (yellow) and CAN_L on CH2 (blue):

For some reason I am seeing a decent amount of 'waviness' on CAN_H but CAN_L seems to be a lot cleaner.

When I measure resistance across CAN_H and CAN_L when the modules are powered off I see a strong and consistent 60R.

I am hoping to please get some feedback on:
1. If there is inherently any serious issue  in my design - happy to provide more information/clarification if needed.

2. Could what is being shown in the capture above be a reason for the packet drops?

3. Any recommendations on what to look for and how to solve the 'waviness' of CAN_H.

Thanks in advance!

  • 0
    TI__Expert 7705 points

    Hi Gideon,

    There is no serious issue in your design. But the "waviness" of CANH is mostly likely caused by common mode noise. I recommend to place a common mode choke between the transceiver and terminations to dampen the reflection, usually the value is 51uH or 100 uH. Common mode noise can affect signal integrity and yes there it is possible that CAN controller recognize it to be error bit. Please let me know if adding CMC helps.

    Regards,

    Sean

  • 0 in reply to Sean Guo
    Prodigy 40 points

    Hi Sean,

    Thanks for your quick reply.

    Interesting, is there any reason why this ringing might be occurring on the CANH and not CANL?

    By the way, even if I disconnect all modules on the bus (except the first one) and I monitor the bus, I still see the same behaviour.

    I am ordering a few samples of all the CMCs from the 1812CAN series to retrofit and do some testing and will report back.

    Regards,

    Gideon

  • +1 in reply to Gideon Kanikevich
    TI__Expert 7705 points

    Hi Gideon,

    Usually this is the ground or cabling issue. Please check them first. And if that node is the only one on the bus, please note that CAN termination requires ~60 Ohms to work normally, with two 60 Ohms split terminations the total will be 120 Ohms on the single end. So you may need to have another 120 Ohm on the other end, or only have one 60 Ohm resistor on this first node.

    Regards,

    Sean

  • 0 in reply to Sean Guo
    Prodigy 40 points

    Hi Sean,

    I was doing some troubleshooting whilst waiting for the CMC and turns out the issue was being caused by the ferrite on the power line into the transceiver. Once replaced with a 0R jumper, the ringing disappeared! 

  • 0 in reply to Gideon Kanikevich
    TI__Expert 7705 points

    Hi Gideon,

    Good to know that! Please let me know if you have further questions.

    Regards,

    Sean