iCoupler isolation in RS-485 applications

The RS-485 bus standard is one of the most widely used physical layer bus designs. The RS-485 standard is specified to drive up to 32 driver/receiver pairs. Although no maximum cable length is specified, lengths of 4,000m are possible. The versatility of the RS-485 makes this design popular for a wide range of applications, especially intersystem connections over long distances.

Because the RS-485 system is typically used to connect multiple systems, and is often run over very long cable distances, isolation between the bus and each system connected is critical. Digital isolation provides crucial isolation and protection from overvoltage transients between the RS-485 cable network and the systems connected to it. Digital isolation also eliminates ground loops in the RS-485 network. Digitally isolating the RS-485 bus from each system connected to the bus reduces signal distortion and errors, and provides system and component protection from system and bus voltage and ground mismatches.

The intention of this application note is to give the user a brief overview of the RS-485 system physical layer, as well as an understanding of why isolation is so important to the system. This application note details how to implement isolation in an RS-485 system using Analog Devices iCoupler products.

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