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ISO7721: ISO7721

Ali Khan
Expert 1140 points
Part Number: ISO7721
Other Parts Discussed in Thread: ISOW7842, ISO7842, ISO1410, ISO6441, ISO6741, ISO7741, ISOW7741, ISOM8110, ISOM8710

Tool/software:

Hi,

I have a GPS NMEA 0183 RS422 device(talker). I need to connect 6 devices(Listener) with GPS output. I am designing a board that need the following features.

  1. Isolate the talker with listener
  2. Buffer the talker output so it can drive 6 Listener devices. Usually, it can drive 2 devices without any buffering or amplification
  3. Convert amplified output to RS232/RS422 based on the requirements.
  4. There will be only one way communication i.e. Talker to Receiver(RS422 input to RS232 Output)

Plz, see the attached block diagram for refence.

Can i follow this reference design as a starting point for this board design?
https://www.ti.com/tool/TIDA-060008

If there is any other suggestions, please let me know

Thanks

  • 0
    TI__Genius 17295 points

    Hi Ali,

    Thanks for reaching out. 

    Can you please confirm the isolator device you plan on using? The subject says ISO7721 but the reference design is for ISOW7842

    Ali Khan said:
    Can i follow this reference design as a starting point for this board design?

    Yes, this reference can be used to guide you with your design. From what i understand, you are asking if the isolator can be used in the "buffer" block in the diagram you have attached. 

    Since you will be connecting multiple devices, there are several other considerations you will have to make. For both the ISO7842 and the ISO7721, the ability to drive 6 other listener devices may be difficult. The current output of the isolation would be insufficient to drive those 6 listener devices. If the isolator is between the transceiver itself, then it may be possible to connect multiple listener devices to the same bus.

    Some additional description of your block diagram and detail on where the isolator is being placed will help clarify the above point. 

    Additional Resource: https://www.ti.com/lit/ug/tiduct4a/tiduct4a.pdf?ts=1747709900469

    Regards,
    Aaditya Vittal

  • 0 in reply to Aaditya V.
    Expert 1140 points

    Hi
    I am open to use any solution.
    Thanks

  • 0 in reply to Ali Khan
    TI__Mastermind 28505 points

    Hello Ali, 

    As Aaditya mentioned. Can you please include come additional details and a block diagram on where the isolator will be used in your system? 

    In general, the ISO1410 family can be used to isolate a RS422/485 bus and act as a transceiver to a controller. The RS422 protocol will allow multiple listener devices to be connected and listen to the same bus signal easily. 

    Best,
    Andrew 

  • 0 in reply to Andrew J
    Expert 1140 points

    Hi @Andrew J 
    Plz, see the detailed block diagram for your reference.
    You are right about RS422 protocol that it allows multiple devices but there are some devices that are limited to provide up to 2 devices safely and sometimes up to 3 devices.

    So we want to buffer the data so we can connect with multiple Listener devices without any problem. The isolation is important on both sides because we don't want to transfer any problem to any connected devices because it is very important.



    This device do the most of the functions that we are developing but we need some extra functions so we are making our own custom board for it.

    https://actisense.com/products/nbf-3-nmea-0183-buffer/?srsltid=AfmBOopsLpj7MpDsq1wa3N6Wdk2ahKbLzxfb_GaNmEt04ekQbXrtCo9t

    Thanks

  • 0 in reply to Ali Khan
    TI__Expert 7325 points

    Hi Ali,

    May 26, Monday is a Holiday in US.

    We Will Review your inputs and get back to you by May 27, Tuesday.

    Regards
    Varun

  • 0 in reply to Varun Kumar
    TI__Genius 17295 points

    Hi Ali,

    Thanks for reaching out and sorry for the delay.

    Thanks for sending the block diagram as well.

    For the top row of isolators: Since the RS422/RS232 transceivers are separate devices, you can use the TI digital isolators to isolate the signal lines . Some choices would be:

    • ISO6441: newest generation of TI digital isolators, supports up to 100Mbps, overvoltage tolerant inputs
    • ISO6741: various supply voltage options, supports up to 50Mbps
    • ISO7741: various package options, supports up to 100Mbps

    it is still unclear about what each isolator requirement is, but the above list is a general breakdown of some of our most popular digital isolators.

    As Andrew mentioned in the previous post, we also have isolators with integrated transceivers, such as the ISO1410. We also have digital isolators with integrated DC/DC converter, such as the ISOW7741. 

    Regards,
    Aaditya V

  • 0 in reply to Aaditya V.
    Expert 1140 points

    Hi
    Thanks for the reply.
    I want to use ISOW7741 but the input supply that i have is 12V. Also, isn't' it CMOS logic level while I have RS422 input. Can you clarify that plz?
    I need RS422 transceiver that can receive RS422 input and isolate it for the next stage. Let's not convert output to RS232 for now. I want isolation between talker and Listener.
    One talker can be directly connected with Listener up to 2 devices but I am adding isolation for extra protection.

    If you need more details about the end product then let me know. I will explain further.
    Thanks




  • 0 in reply to Ali Khan
    TI__Genius 17295 points

    Hi Ali, 

    Since you require 12V supply, the ISOM8110 opto-emulator would be a good fit. These device support a significantly larger voltage range and do not require a supply pin. However this device is technically a "one channel" device, Therefore your application may require multiples of these devices. https://www.ti.com/product/ISOM8110

    The ISOM8710 is also another option since the output of this device provides logic 0-5V signals: https://www.ti.com/product/ISOM8710

    Another solution is to step-down your supply voltage to for the requirements of the ISOW7741 or other digital isolators from my previous posts.

    Regards,
    Aaditya V.