Implementing Gigabit Power over Ethernet to achieve EMC compliance – Part 2
Summary
To investigate the EMC properties of the Gigabit Power over Ethernet interface, Würth Elektronik started by developing and implementing its own reference design RD022 [3]. Conducted interference emission at 12 V and 2 A output current with long filtered load lines The reason for this behaviour results from the design of the isolated converter. The return current path to the source is via the Ethernet cable and its termination using the AAN (Asymmetric Artificial Network – 150 Ohm common-mode impedance). The situation outlined leads to the power supply on the PoE board being extended with a filter to guarantee compliance with the conducted interference emission limits. Extension of the board with copper sheet as the shielding plate and filter components The capacitor for short-circuiting the primary and secondary GND layers should in principle be significantly larger (typ.
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