The LTC®4259A is a quad –48V Hot Swap™ controller designed for use in IEEE 802.3af compliant Power Sourcing Equipment (PSE). It consists of four independent ports, each with output current limit, short-circuit protection, complete Powered Device (PD) detection and classification capability, and programmable PD disconnect using AC or DC sensing. Used with power MOSFETs and passives as in Figure 1, the LTC4259A can implement a complete IEEE 802.3af-compliant PSE. The LTC4259A can operate autonomously or be controlled by an I²C serial interface. Up to 16 LTC4259As may coexist on the same data bus, allowing up to 64 powered Ethernet ports to be controlled with only two digital lines. Fault conditions are optionally signaled with the INT pin to eliminate software polling. External power MOSFETs, current sense resistors and diodes allow easy scaling of current and power dissipation levels and provide protection against voltage and current spikes and ESD events. The LTC4259A is available in a 36-pin SSOP package. Linear Technology also provides solutions for 802.3af PD applications with the LTC4257, LTC4257-1 and LTC4267.