• State TI Thinks Resolved
  • Locked Locked
  • Replies 1 reply
  • Answers 1 answer
  • Subscribers 32 subscribers
  • Views 183 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TCAN4550: Regarding compatibility of communication between different voltage CAN lines

Jayam Srivastava
Prodigy 90 points
Part Number: TCAN4550
Other Parts Discussed in Thread: TCAN334

Hi all,

I am currently using TCAN4550 coupled with an ST controller(STM32F0) for my setup and it is working fine with around 50 nodes on the line. 

Recently I have started working with STM32G0 family , and it is having CAN-FD built in with the controller, so I have implemented communication using that separately; using TCAN334GDR transceiver and it is also working fine . What I noticed is that the idle voltage of CAN-H and CAN-L lines in the first case is 2.5V and is around 1.65V in second case (CAN-FD). So, I wanted to know if these are inter-compatible and I can use both of my boards interchangeably or not. If there is any probable issue with this communication or anything I will need to change before trying to do so, please let me know.

Thank you.

Regards 

Jayam Srivastava.

  • 0
    TI__Guru 50555 points

    Hi Jayam, 

    Good question here. The short answer here is yes; it is possible to use both 5V supplied transceivers (like TCAN4550) and 3.3V supplied transceivers on the same bus.

    Because a 3.3V supplied CAN transceiver is not capable of driving the same voltage levels, the common-mode {(CANH + CANL) / 2} that it drives on the bus is also lower. It's also good to note that TCAN334 drives a recessive level of Vcc/2 (1.85V) vs the typical 5V recessive level of 2.5V. Therefore, in a mixed network, we would expect to see some recessive level in between these two biases. It gets a little trickier in the active case where one node has won arbitration and is driving the bus on its own. When either a 5V or 3.3V transceiver is driving dominant, it overpowers the recessive bias of all other transceivers and forces the bus common mode to it's own driven value (most often Vcc/2). This is likely what you're seeing when you see the voltages switch from 2.5V to 1.65V. 

    From the perspective of data integrity, this is not too impactful as the differential signal is not affected too drastically. The common-mode shifting around does have some implications for emissions so this is generally the largest concern when running a mixed network like this. 

    Let me know if this explanation is clear and if you have any more questions.

    Regards,
    Eric Schott