Thermal protection of an 80V silicon-on-insulator LDMOS transistor for power-over-Ethernet applications

This paper describes thermal protection for the pass transistor of a power-over-Ethernet powered device controller developed on a bonded-wafer silicon-on-insulator process. The 1Ω, 80V LDMOS transistor dissipates up to 8W during a typical fault condition. Current limiting, tightly coupled over-temperature sensing, and drain-to-source voltage sensing combine to limit measured peak junction temperatures to less than 250°C.