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TCAN4550: CANbus isolation and repeater design

Paul Lu
Prodigy 20 points
Part Number: TCAN4550
Other Parts Discussed in Thread: ISO1044

Tool/software:

Hi TI

I'm looking to extend my CANbus routing and need a solution with isolation and repeater capabilities.

Does TI offer any application notes, reference designs, or product recommendations to support this?

Thanks,

Paul

  • 0
    TI__Mastermind 33030 points

    Hi Paul,

    The issue with a CAN repeater comes from handling the bus arbitration protocol.  This generally requires two CAN transceivers with some "glue logic" in between that allows the levels of the TX and RX pins to pass correctly.  This concept is the same with our without isolation which is just an additional block in the signal path.

    TI Does have an Isolated CAN FD Repeater Reference Design (Link) demonstrating this concept and a discrete solution to this application. The timing and performance in this design may be limited due to the multiple discrete components and layout used for this reference design, and integrating the Glue Logic portion into a better solution using a programmable logic device may be needed if you need to support fast CAN bus bit rates.

    Regards,

    Jonathan

  • 0 in reply to Jonathan Nerger
    Prodigy 20 points

    hi Jonathan, 

    Thank you for your kind reply.

    One more thing I’d like to check with you is the application topology.

    Based on the block diagram from the Isolated CAN FD Repeater Reference Design, I assume it should support chaining on the same CAN bus. Also, the end device should be replaceable with a TCAN4550 and connected to a MCU as shown below, right?

  • 0 in reply to Paul Lu
    TI__Mastermind 33030 points

    Hi Paul,

    Multiple devices are always "chained" on the same CAN bus and this is the normal application for CAN, so I would say yes. 

    Also, yes an MCU and TCAN4550 can be connected through SPI and to the Bus Arbitration logic when used in a test mode to bypass the internal CAN FD transceiver.

    However, I don't understand the larger application because this just looks like you are trying to isolate multiple CAN transceivers on the same bus.  If all you need is isolation, then the repeater approach seems like it would be more complex and you could simply isolate the CAN transceiver or use an isolated CAN transceiver (Link)?

    Regards,

    Jonathan

  • 0 in reply to Jonathan Nerger
    Prodigy 20 points

    Hi Jonathan, 

    I'm looking for solution provides both isolation and repeater. so the best way to approach this idea probably be like TI's reference design. 

    or is there any simplest way (product) for it?

    Thanks

  • 0 in reply to Paul Lu
    TI__Mastermind 33030 points

    Hi Paul,

    OK, understood that you do want the repeater in addition to isolation.  We don't have a standalone CAN repeater device.  But we do have Integrated Isolated CAN transceivers.  Occasionally there is confusion about adding isolation to a CAN bus and if isolation is all you wanted, then you could do that without the need for a repeater.

    Regards,

    Jonathan

  • 0 in reply to Jonathan Nerger
    Prodigy 20 points

    Hi Johathan, 

    I'd like to design the system with a "master-polling → response → silent" structure, where the CAN bus is selectively enabled or disabled via a MUX. I assume the termination would be placed behind the MUX. Could you recommend a solution to ensure the CAN bus remains in a high-impedance state when disconnected? Additionally, what potential risks should we be aware of in this approach?

  • 0 in reply to Paul Lu
    Prodigy 20 points

    additional for Isolated CAN FD Repeater Reference Design (Rev. A)

    my understanding is it should be able to replace with a ISO1044 as below, is it correct?

  • 0 in reply to Paul Lu
    TI__Mastermind 33030 points

    Hi Paul,

    Yes I believe your understanding is correct.  The ISO1044 device integrates both the isolation and CAN transceiver into a single device.  I believe the reference design was done prior to the development of the ISO1044 or other isolated CAN transceiver which is why it has both a separate isolation and CAN transceiver.

    Regards,

    Jonathan