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Question about isolated Profibus Tranceiver

g.f.
Guru 15510 points
Other Parts Discussed in Thread: PROFIBUS, ISO1176T, SN65HVD72, SN65HVD82

Hi,

I have a question about "isolated Profibus Tranceiver with integrated transformer driver"- ISO1176T.

We are using ISO1176T for PROFIBUS.
Now, we are thinking to use ISO1176T for "isolated RS485" as general purpose but not PROFIBUS.
Is it possible to use as general puropose?
If there are any limitation please let me know.

best regards,
g.f.

  • 0
    TI__Mastermind 21523 points

    Hi G.F.,

    I am no expert on PROFIBUS but there have been a couple threads on this topic in the past. I found an internal thread on this topic and pasted a portion of it below.

    The main difference between RS 485 and PROFIBUS is the differential output voltage, VOD, which you mention.  The Profibus spec is somewhat larger than the RS-485, but the receiver input sensitivity is still -200mV to -10mV, so a larger VOD makes no difference.

    It looks like profibus requires a higher VOD voltage spec on the driver than RS485 does but both traceivers have the same input threshold. This means that using a PROFIBUS transceiver in RS485 should be no issue. If I find out any other differences I will follow up.

    Thanks,

    John

  • 0
    TI__Mastermind 28265 points

    Hello G.F.

    the only drawback with fast transceivers such as ISO1176T is, that the short rise and fall times of 3ns (typ) will cause significant EMI into adjacent circuits when using the device in long distance bus segments.

    For long distances (500m to 1km) I recommend transceiver with transition times around 1us and data rates up to 100 kbps maximum.

    Best regards, Thomas

  • 0 in reply to Thomas Kugelstadt
    Guru 15510 points

    Hi John and Thomas,

    Thank you so much for the details.

    I'm sorry but let me ask again to make me sure.
    So, it can be judged by distance of bus whether it can be use as general purpose RS485 tranceiver.
    Which means ISO1176T can be used as general purpose isolated RS485 tranceiver
    if distance of bus is less than 500m. But if distance of bus is long(500m to 1km),
    I should use other isolated RS485 tranceiver. Is my understanding correct?

    best regards,
    g.f.

  • 0 in reply to g.f.
    TI__Mastermind 28265 points

    Hello G.F.

    to be very precise you could use the ISO1176T even in long distance cable runs simply by reducing the data rate drastically to around 100kbps or even lower. However, the fast rise and fall times of the driver still remain.

    If you were running your cable parallel to a 24V DC power line or 120/240V AC power line these transients would not matter too much either. An EMI issue could easily occur however, when any one of your bus nodes begins transmitting data while being in close proximity to EMI sensitive electronics. This adjacent electronics could pick up the switching transients from the active RS-485 driver in safety and security applications and other alarm systems could cause unwanted triggering of alarm procedures. For this type of application specific EMI regulations exist. And in these applications you would preferably use transceivers such as SN65HVD82 (5V) or SN65HVD72 (3.3V) transceivers with longer rise/fall times of 1us.

    best regards,

    Thomas

  • 0 in reply to Thomas Kugelstadt
    Guru 15510 points

    Hi Thomas,

    Thank you so much for the detail.
    I understood.

    best regards,
    g.f.