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ISOW7841: Isolation

Sam Rhoufiry
Prodigy 40 points
Part Number: ISOW7842
Other Parts Discussed in Thread: ISOW7841, TIDA-00892, ISO1410

I have a couple of questions:

1- Can this isolator work on an rs-422 network?

2- Can I just insert the isolator in an rs-422 network to add isolation?  2 pairs rs-422_tx and rs-422_rx

  • 0
    TI__Guru 55575 points

    Hi Abdel,

    ISOW78xx family of devices isolate digital CMOS channels and in addition they also provide isolated DC/DC power. When you use an RS-422 transceiver along with ISOW78xx then you can achieve isolated RS-422 solution. So to answer your questions,

    1. ISOW7841 doesn't drive an RS-422 bus directly but it can work in conjunction with an RS-422 transceiver.
    2. Your RS-422 network might already have RS-422 transceiver connected to MCU in each node. Inserting ISOW7841 in-between the MCU and RS-422 transceiver would help you achieve isolated RS-422 solution.

    Please do have a look at the below TI Design that implements isolated RS-485 transceiver using ISOW78xx. Since the schematic between RS-485 and RS-422 remains pretty much the same, you can use TIDA-00892 as a reference for your application. Thanks.

    www.ti.com/.../TIDA-00892


    Regards,
    Koteshwar Rao

  • 0 in reply to Koteshwar Rao
    Prodigy 40 points
    Do you have isolators that can drive rs-422/rs-485 signal levels?
  • 0 in reply to Sam Rhoufiry
    TI__Guru 55575 points

    Hi Adbel,

    Yes, we do. We have a few isolated RS-485 transceivers that integrate digital isolator and RS-485 transceiver together into a single package. You can find more details about these products at the link below. All of the listed RS-485 transceivers can also be used for RS-422 applications. Please note that these devices do not integrate power hence power needs to be supplied externally to both VCC1 and VCC2.

    www.ti.com/.../products.html

    Among the above devices, ISO1410 is one of our latest isolated RS-485 transceivers that provide the best isolation specs, best EMC and other performance improvements. Let me know if you have any questions on these, thank you.


    Regards,
    Koteshwar Rao

  • 0 in reply to Koteshwar Rao
    Prodigy 40 points
    I meant rs-485 to rs-485 isolation (no TTL levels)
  • 0 in reply to Sam Rhoufiry
    TI__Guru 55575 points
    Hi Abdel,

    I see you are looking for an RS-485 bus isolator and not an isolated RS-485 transceiver. Unfortunately, we do not have a single chip solution that can isolate the bus independently.

    The most common practice is to isolate the bus at a communication node and most communication nodes generally have an MCU. Hence it is common to find isolated transceivers than the RS-485 bus isolators. I agree that there can be situations where one would want to use a device to isolate the RS-485 bus like a repeater is used, situations like this can be addressed by using the approach described in below TI design.

    www.ti.com/.../TIDA-00333

    Hopefully this meets your requirement, let me know if you have any questions. Thank you.


    Regards,
    Koteshwar Rao