Adapter PCB for filtering electromagnetic interference on an RS-485 interface

ANP083

As a result of the constantly growing number of applications based on networked communication via data lines, it is becoming increasingly important to ensure trouble-free operation as well as the safety of electrical systems and devices. By filtering directly at the interface, interference emissions, electrostatic discharges (ESD) and fast transients (burst) are prevented from entering the system and thus negatively influencing the operating performance. To verify the EMC properties of electrical systems, special tests are carried out in accredited EMC test laboratories. If these tests are not passed, the application has to be revised. In order to simplify this process, an adapter stick was designed which contains a complete filter circuit for the selected application and can be plugged into the appropriate interface. The simple plug-in allows a quick check of the filter effect on the system to be tested. Once the tests are passed with the filter stick inserted, the circuit can be implemented in the system.

This application note describes the design of such a filter stick for the RS-485 transmission standard. Since no connector is defined for RS-485 applications, 9-pin D-SUB connectors and the pin assignment defined by PROFIBUS, have been selected. This ensures the widest possible range of applications.

Download the Layout and the BOM for the complete RS-485 Profibus EMI & ESD solution