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Ethernet-Slide18

Littelfuse recommends that the bias be connected to the SEP through 1MOhm bias feed resistors. This will satisfy most isolation requirements. The bias supplies may be ground referenced or floating and should be as high a voltage as possible as long as the differential total voltage does not exceed the SEP device Vdrm rating. For 8V SEP devices, a 5V supply is best. For 72V SEP devices, it is recommended that the PoE supply be used as the bias supply. One caveat is that during surge conditions, the peak voltage across the SEP device may be impressed across the bias resistors. Therefore, it is recommended to use resistors rated to at least 100V for the bias resistors. Generally this means an 0805 resistor but the designer should check their resistor specifications to be sure.

PTM Published on: 2011-10-31