PoE subsystems are required to be electrically isolated, so traditional PSE designs usually require up to six expensive optocouplers and an isolated 3.3V supply to isolate the I²C digital interface. However, Linear Technology’s 8-port LTC4290/LTC4271 and 12-port LTC4270/LTC4271 PSE controller chipsets take a cost-effective approach to the isolation requirement by physically separating the digital and high voltage Ethernet interfaces into two ICs, and then bridging the ICs with an inexpensive 100Base-T Ethernet transformer. It is this transformer-isolated communication protocol that replaces the expensive optocouplers and the isolated 3.3V supply used in traditional designs which results in significant bill of materials (or BOM) cost savings.