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ISO1410DWEVM: Does the part support DC Common Mode Volatge upto 1.5KV

Santanu Dutt
Prodigy 10 points
Part Number: ISO1410DWEVM
Other Parts Discussed in Thread: ISO1410

I am using this part in an environment where the DC common mode floating voltage incident on the chip inputs can go up to 1500V. There can be about 200 units connected on the RS485 bus. My queries are:

  1. Will the chip function in this environment?
  2. I notice that the isolation is capacitive in nature. Will using an optoisolator with a non-isolated transceiver be a better option considering the DC voltage?
  3. The Ground of each unit connected on the bus is floating. In that case, how will the reference voltage be made available to each unit?
  • 0
    TI__Intellectual 2160 points

    Hi Santanu,

    1. Will the chip function in this environment? 

             If you are talking about ground potential difference, then it can handle. The bus signals wrt GND1 can be higher or lower by 1500VDC which is the VIOWM of the device. If you are talking about the DC common mode on pins A or B wrt GND2, then it shouldn't exceed -7V/12V.

    2. I notice that the isolation is capacitive in nature. Will using an opt isolator with a non-isolated transceiver be a better option considering the DC voltage?

      TI isolators use capacitive isolation. The input signals are modulated to a higher carrier frequency and then transmitted. So even a DC voltage can be reliably transmitted. Optoisolators degrade over time, but TI Isolators are rated for much better TDDB with very less degradation over time. I would suggest using our Isolated interfaces for a compact and easy solution.
    3. The Ground of each unit connected on the bus is floating. In that case, how will the reference voltage be made available to each unit?

      RS485 uses differential signaling and doesn't need the GND of each unit connected to each other on the bus. But if you connect via a small resistance, then it will restrict current in the GND loop and have a better immunity to common mode noise.

    Thanks

    Vikas J

  • 0 in reply to Vikas Jeevannavar
    Prodigy 10 points

    Vikas,

    Thanks for the reply - really helped. Just wanted to clarify that the 1500V I was talking about is with reference to the floating ground connected to each unit. The ground voltage difference between the first and the last unit connected on the bus can go upto 1500V. What happens if the voltage difference exceeds 1500V (a rare possibility but can happen)

  • 0 in reply to Santanu Dutt
    TI__Intellectual 2160 points

    Hi Santanu,


    The floating ground connected to each unit will support common mode voltage of -7V/12V wrt to GND2 and device gets damaged beyond ±18V. Hence, you cannot use ISO1410 in your application.

    May I know the application in which bus common mode goes up to 1500V?

    Thanks

    Vikas J

  • 0 in reply to Vikas Jeevannavar
    Prodigy 10 points

    Vikas,

    The application is an aluminium smelter where there are about 300 pots (an electrolytic unit) in series. Each pot has a controller and the voltage generated from the pot is about 5 volts. Therefore, the potential difference between the first and last pot is about 1500V even though the voltage difference between adjacent pots is about 5V

  • 0 in reply to Santanu Dutt
    TI__Intellectual 2160 points

    Hi Santanu,

    Thank you for the information. In my knowledge, none of the RS-485 bus or devices support this unusual requirement. ISO1410 is one of the robust devices for isolated RS-485 communication.

    May be a block diagram with voltages mentioned at nodes will help us resolve your concern better.

    Thanks
    Vikas J