Digital isolation/RS485 technology
1 June 2005
Circuit & System Protection
Typically, RS485 technology is 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 critical isolation and protection from overvoltage transients between the cables and the systems connected to them, while eliminating ground loops in the RS485 network. Digitally isolating the RS485 bus from each system connected to the bus reduces signal distortion and errors, providing system and component protection from system and bus voltage, as well as ground mismatches.
Analog Devices' ADM2483/ADM2486 RS485 transceivers are digitally isolated to reduce reflections with improperly terminated transmission lines. The ADM2483 device's input impedance is 96 kΩ, allowing up to 256 transceivers on the bus. Its driver has an active high enabling feature. The driver differential outputs and receiver differential inputs are connected internally to form a differential I/O port. When the driver is disabled or when VDD1 or VDD2 = 0, minimal loading is imposed on the bus, and an active high receiver disables, causing the receive output to enter a high impedance state, resulting in loss of power.
The devices in 16-lead SOIC have low power operation of 2,5 mA and are suitable for 5 V or 3 V operation. They have high common-mode transient immunity (>25 kV/μs).
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