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The RS-485 interface works using differential signaling which is effective in rejecting common-mode noise making it a popular choice for long-distance communication. RS-485 transceivers currently come with many different features a designer can choose from. This application note will help designers understand how features like fault protection, input common mode ranges, and deglitch enables can help designers to create a more robust RS-485 system. In this application note, each feature is discussed and lab tested using THVD24x0 devices (supports the listed features) with results. THVD2410 and THVD2450 are ±70-V fault-protected, half-duplex, RS-422/RS-485 transceivers operating on a single 3-V to 5.5-V supply. By leveraging these useful features, the RS-485 system design become much easier and the system is more robust.
In some applications, the RS-485 bus might be exposed to high voltage, due to various reasons like direct shorts to power supplies, mis-wiring faults, connector failures, damaged cables, and tool mis-applications. The ±70-V fault-protection of THVD24x0 means that bus interface pins are protected against up to ±70-V DC overvoltage conditions mentioned above. For example, the A and B pins are accidentally shorted to 48-V power supply in an industrial automation equipment. THVD24x0 devices will not be damaged in this fault condition. As the communication fails, the fault condition can be detected and cleared. After the 48-V DC short is resolved, the devices resume working normally without requiring a power cycle.