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TCAN1042GV-Q1: How long is the wire distance limit when two TCAN1042 RX and TX connection is off board?

Iris Shen
Expert 4002 points
Part Number: TCAN1042GV-Q1

Hi team,

I'd like to confirm if our TCAN1042 can support off board TX and RX connection? For example, we have LED driver on one board and TCAN1042 on another board, we want to connect the TX and RX by wire about 10cm~20cm. Is it applicable?

Thanks.

  • +1
    TI__Guru 53555 points

    Hi Iris,

    There is nothing inherently wrong with sending the digital signals through a cable from the CAN controller to/from the transceiver. However, it is good to keep in mind what impact this might have on the signals and how this is related to the CAN signal and its specifications. Primarily what will happen here is an increase in signal line capacitance, inductance, and ultimately propagation delay. This should be the major focus of adding a relatively short cable distance on these digital signals. While estimating this behavior with cable characteristics and impedance values, you will get the most accurate representation by conducting experimental trials on the proposed setup. I would recommend measuring the effective propagation delay of a prototype setup using similar traces and cables that the final design will use. Given that we use very similar setups when evaluating out transceiver with our EVMs (TCAN1042EVM would likely be helpful for this test setup), I don't expect such a short connection would cause any major issues on this front unless the system is already at it's limits (high data rate, large network, etc.). 

    As for the limits of this delay for CAN, you may reference the app note linked below for more information. It discusses how propagation delay introduced by digital isolators is handled, but the effect of this cable delay will be similar. 
    https://www.ti.com/lit/an/slla479/slla479.pdf?ts=1650890891147&ref_url=https%253A%252F%252Fwww.google.com%252F 

    The secondary thing to consider when taking any signal off-board like this is how it impacts electromagnetic compatibility (EMC). While digital signals are more resilient to external electromagnetic interference, they will also have very different emissions characteristics than a differential CAN signal. The hope is that these cables are all internal to an EMC housing so the impact of this overall will be minimized, but it is certainly another factor to account for with such a solution. Let me know if you have any questions or concerns regarding this. 

    Regards,
    Eric Schott

  • 0 in reply to Eric Schott1
    TI__Expert 4002 points

    Hi Eric,

    Thanks for your detailed explanation. I asked this question because my customer wanted to use off board design so that they can reduce a TCAN IC and cost down. But as you mentioned, the concern we have is about EMC performance of this design, as well as BCI test performance(it is a rear light application). So I suggested customer not to design this way. 

    By the way, I am interested if you have done EMC test in similar application? And how did it perform? Thanks!

  • 0 in reply to Iris Shen
    TI__Guru 53555 points

    Hi Iris,

    I'm not aware of any EMC testing we've done with digital signals connected through off-board cables. Generally, any design method that is suboptimal for EMC is avoided during such tests so that only the performance of the transceiver itself is being evaluation. I would certainly be interested to see what kind of difference this would make, especially when comparing a solution with cabling inside and outside a metal housing. However, I don't see an opportunity in the near future where I could set up such a test. 

    Regards,
    Eric Schott