• State
  • Locked Locked
  • Replies 6 replies
  • Subscribers 33 subscribers
  • Views 268 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.

SN65HVD230: Are there any grounding potential considerations using multiple non-isolated XCVRs with an isolated XCVR on the same CAN bus?

oscar n
Prodigy 70 points
Part Number: SN65HVD230
Other Parts Discussed in Thread: TCAN334,

Hello, can multiple non-isolated SN65HVD230D CAN XCVRs be used with an upstream isolated CAN XCVR without any issues? I am currently experiencing an issue where there is coupled switching noise and have CAN frame dropouts with this setup despite using properly shielded CAN harnesses + termination. Curious if there's any grounding/signal integrity considerations I'm missing with this setup, thanks.

  • 0
    TI__Guru 50795 points

    Hi Oscar,

    While the CAN signal itself is only dependent on the differential voltage between CANH and CANL, all CAN receivers also have a limited common mode range for the individual voltages on the CAN lines with respect to GND. If the common mode of the CAN bus falls outside of this range for any transceiver with respect to its local GND, it will be unable to interpret CAN data. This limit is included on the datasheet for all TI transceivers and is between -2V and +7V for SN65HVD230. A similar device with a greater common mode range would be the TCAN334 family of 3.3V transceivers. These transceivers have a common mode range of +-12V and will give more margin for ground potential differences between nodes.

    I would also recommend measuring the actual voltage at the transceiver pin to ensure this common mode range will be sufficient and no datasheet maximum values are being violated.

    Let me know if you have any more questions. 

    Regards,
    Eric Schott 

  • 0 in reply to Eric Schott1
    Prodigy 70 points

    Thanks Eric. If we are seeing noise or a on the lines past the -2V and 7V limit, I'm assuming there are internal clamps on the SN65HVD230 that would be clamping those voltages down? Wouldn't this mean it would still be able to interpret CAN data? (I understand this may also damage the input stage as well then?)

  • 0 in reply to Eric Schott1
    Prodigy 70 points

    Hi just to follow up, it looks like the recommended limit in the datasheet is -2V to +7V for common mode, but the absolute maximum is -4V to 16V. However, you mention that exceeding the -2V and +7V limit will cause the transceiver to be unable to interpret CAN data. Can you confirm if exceeding the recommended limits, but not necessarily the absolute maximum limits, will cause a CAN failure?

  • 0 in reply to oscar n
    TI__Guru 68972 points

    Oscar,

    Only exceeding the absolute maximum limits will potentially cause damage. Exceeding the recommended operating conditions will cause the CAN receiver to not interpret data correctly. Exceeding the recommended limits will not damage the device as long as the voltage is still within the absolute maximum limits.

    Regards,

    Eric Hackett 

  • 0 in reply to Eric Hackett
    Prodigy 70 points

    Hi Eric, is there anything definitive that TI can definitively provide or say that exceeding the SN65HVD230's -2V and 7V limits will cause an interpretation failure? The datasheet only states that the -2V and 7V specification are from the ISO11898-2 standard, and that the XCVR conforms to that standard. Are you saying that exceeding the -2V and 7V spec actually will cause or trigger a failure? Thanks

  • 0 in reply to oscar n
    TI__Guru 68972 points

    Oscar,

    Yes, those are the defined limits to meet bare minimum for a CAN transceiver, and in our older CAN devices that's what was targeted. The receiver on these transceivers was designed to only be able to interpret in that voltage range. What will happen is that the RXD pin will not report the CAN bus information correctly, thus causing an error in the controller because it won't receive the bit back that it sent.

    Regards,

    Eric Hackett