RS-485 driver for a long distance

Hello,

Our customer if looking for a RS-485 transceiver to transmit 1Mbs for a 1 km of cable. Which products can  I recommend?

There are some special products from TI and Maxim, but what about same solutions from ADI?

Regards,

Evgeny

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  • Hi Evgeny,

    Do you know what cable they are using? It will help if we know the attenuation in the cable. If you are looking for transmitting over long distances at higher data rates, I recommend the MAX2250xE family (ADI has now acquired Maxim Integrated). The MAX2250xE family is optimized for high-speed (up to 100Mbps) communication over long cables. It has integrated pre-emphasis circuitry that extends the distance etc.

    Regards,

    Naveen 

  • Hi Naveen,

    Thanks for the reply,

    The customer is aware about Maxim parts however we are not allowed to purchase these parts right now. And we have no forecast when it is available for us.

    their question was related to ADI parts for long distances.

    I will specify cable parameters.

    Regards,

    Evgeny

  • Hi Naveen,

    they use a local type of a cable with a name МКЭКШВнг-LS 1х2х1,0.

    A general description could be found there https://www.avtoprovod.com/en/production/catalog/type97

    There is an information: Electrical cable insulation resistance for a length of 1 km at a temperature of 20°С shall be not less than 10 MΩ

    Regards

    Evgeny

  • Hi Evgeny,

    Unfortunately, that cable cannot be used for a long distance transmission.  According to the specs, the cable is suitable for communication only up to 400Hz, and the attenuation at > 1kHz is too high to transmit any RS-485 signals over that distance. Here's the attenuation spec for that cable: 

    You'd probably need a cable with less attenuation. I also recommend placing a repeater somewhere close to the middle of the cable. At 1 Mbps, with a conventional RS485 driver, you can transmit signals over a distance of at most 1500 ft. That's less than half a kilometer. You need to look for a driver with pre-emphasis, but a repeater is strongly recommended.

    Regards,

    Naveen