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Isolated component for SN65HVD22

Idan Ozana
Intellectual 480 points
Other Parts Discussed in Thread: SN65HVD22, ISO15

Hi,

I'm looking for communication that can handle a network with ~250kbps for one 10km segment (very large scale network).

In your website, I found the SN65HVD22, Extended Common-Mode RS-485 Transceivers that might be suitable for my application. My problem is that because of the long distance I need it to be Isolated (I think…), do you have any isolated transceivers that will be suitable for this one (see Figure 5 and Figure 6 for example)?

The same question, for pre-emphasis or other advance drivers for long distance- long data rate.

Thank you,

Idan 

3000.Data-rate independent half-duplex repeater (TI).pdf    

  • 0
    TI__Mastermind 28265 points

    Hello Idan,

    I see you started a second thread for the same network design challenge. Can we combine the two threads and focus on one thread only, otherwise it might get confusing getting some answers to your request in one thread and some further answers in another thread.

    For now let me answer this thread and then continue on the other "main" thread.

    1) Segment Length

    Your initial thought on splitting the 10km distance into multiple segments is correct. The problem with one 10km segment is that you will not have any signal left at the end of the segment because of the insertion losses of the cable. The typical 'cable length versus data rate' characteristic shows a maximum length of 4000 ft or 1200 m for an AWG24 cable. The reason for this maximum length is that the resistance of the cable builds a voltage divider with the termination resistor at the receiving end. At 1200 m, the initial bus signal sent by the driver is reduced down to half its original value, that is an attenuation of 6dB. If you simply multiply this value by a factor of 8 (8 x 1200m = 9600m ~ 10km) your total attenuation would be 48db, so almost 0V amplitude.

    2) Extended Common-mode or Isolated Transceiver

    Extended common-mode transceivers are great if you know for certain that the maximum difference in ground potential between remote bus nodes will not be larger than the transceiver's input common-mode voltage range.

    If you do not know the maxim possible ground-potential-difference (GPD) it is better to use galvaically-isolated transceivers. These devices have their control logic circuitry internally isolated from the bus driver and receiver section. In the case of an isolated bus there are no common-mode potentials between the bus transceivers, which allows you to either chose any standard RS-485 transceivers in combination with stand-alone digital isolators, or transceivers with integrated isolation.

    Now let's continue in your first thread "Repeaters in cascade (ISO15)".

    Please let me know whether I can close this thread.

    Thank you, Thomas