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Isolated USB to RS485 two wire

Muhammad Naeem74
Prodigy 120 points
Other Parts Discussed in Thread: ISOW7841, THVD1410, ISO1410, TUSB3410

Hi

I was wondering if TI have a reference design or application note for an isolated USB TO RS485 (2 wire) design.

Thanks in advance

Best Regards

  • 0
    TI__Intellectual 2325 points
    Hi Muhammad,

    Thanks for using our E2E forums.
    Unfortunately, it doesn't look like we have what you are requesting - sorry about that ! Will let you know if we find so otherwise.

    Do you have some flexibility with the approach to this end system? If it's possible, - can you let us know more about the end system goals and constraints [eg: data rate, isolation level, link length? It may help us to see if an alternative solution exists or is possible .

    Best regards,
    Abhi
  • 0 in reply to Abhi Aarey
    TI__Intellectual 2325 points
    Hi Muhammad,

    Just to follow-up here, no we don't have an exact solution to match your request. Please let us know if you have any flexibility here: that is if you are open to using a USB to Serial Port chip and then from that to an Isolated RS485 ?



    Regards,
    Abhi
  • 0 in reply to Abhi Aarey
    Prodigy 120 points

    Hi Abhi,

    Thanks for your replies.

    that is if you are open to using a USB to Serial Port chip and then from that to an Isolated RS485 ?

    Yes, there is flexibility in the system, I am open to using a USB to serial port chip (such as FT232RL), the only requirement is that the design needs to be compact.

    The data rate in only 9600 bps, RS485 comms is half duplex, line length is only a few meters.

    What do you think about utilising ISOW7841 for this....

    I am open to other ideas as well, thanks.

  • 0 in reply to Muhammad Naeem74
    TI__Expert 6195 points

    Hi Muhammad,

    I was reading through this thread and I think ISOW7841 can be a very good solution if size is of concern to you for an isolated RS485 system.

    Here is a link for a TI Design for a compact isolated RS485 system with ISOW7841. As you can see from the example board below, the total solution footprint can be quite small. 

    The RS485 transceiver in the design could be swapped out for one meeting your needs. Here is a list of half-duplex RS-485 transceivers TI has to offer. I would start by checking out the THVD1410. 

    Another option is to use an isolated RS-485 transceiver such as the ISO1410 and generate a isolated power supply with a transformer and transformer driver such as the SN6505. An example of how to do this is in the Typical Application Section of the ISO1410 datasheet (page 26). Since this would require a separate transformer, I would expect this solution to be more efficient, but take up more board space. 

    Anthony from my team wrote a document on this very subject actually - How to Isolate Signal and Power for an RS-485 System. 

    Does this answer your question? Let me know if you need any further assistance. 

    Best regards, 

    Dan

  • 0 in reply to Dan Kisling
    TI__Intellectual 2325 points

    Hi Muhammad,

    Good to hear that there are some options to explore. You have good options shared by Dan on the Isolation (with Power) and on the RS485 side. You have a decent baseline here combined with the FT232R.

    Now on that last point, on the USB side, we wanted to check if the TUSB3410 chip (link) will be feasible for you ?
    Functionally similar overall but differences do exist and is not a 1: 1 match.

    If you need further thoughts on the USB side, I recommend checking with our USB team over at the Interface forum (link)

    We hope this was helpful!  I'll go ahead and update the status of this thread for now , but we'll still be here for you if you have follow-up questions! (please use the "ask a relation question" or "ask a new question" if this is the case).

    Regards,

    Abhi

    PS: Edited to fix a typo.

  • 0 in reply to Dan Kisling
    Prodigy 120 points

    Hi Dan,

    Thanks for your reply, very useful info on ISO410.

  • 0 in reply to Abhi Aarey
    Prodigy 120 points
    Hi Abhi,

    TUSB3410 looks interesting, we may utilise it for one of our future projects. I have not yet had a chance to dig into the datasheet, but are there any special requirements for a driver when using this IC?
  • 0 in reply to Muhammad Naeem74
    TI__Guru 53115 points

    Hi Muhammad,

    Abhi is on personal leave for a few days, I will try to help you with your question in his absence.
    To get right and accurate answers on TUSB3410, like Abhi mentioned earlier, we recommend you to post questions related to TUSB3410 in Interface Forum. I am copying below the link to Interface Forum, thanks.

    e2e.ti.com/.../138


    Regards,
    Koteshwar Rao