Demonstration Circuit 609B features the LTC4259A, a quad -48V network power controller designed for use in IEEE802.3af compliant systems. Integrated in a 36-pin SSOP package are four independent channels controlling external N-channel FETs, each with foldback current limiting, inrush current control, fast short-circuit limiting, AC and DC disconnect sense and complete Powered Device (PD) detection and classification capability. DC609B inserts power onto the signal pairs of an existing system to power four IP phones or other PDs. This eliminates the need for an external power source to power the PDs. Should the user find the need to shut off a channel, a momentary shutdown switch for each port disconnects power for the respective port and a Reset switch resets the LTC4259A. The LTC3803 is used in a boost converter topology to generate a +3.3V supply from the -48V supply for the digital portion of the LTC4259A. The I²C interface is used to configure the LTC4259A and read back status to a host controller. Separate data in and data out I²C lines simplify the connection of opto-isolation circuitry. The DC609B is a part of the LTC QuickEval family of Linear Technology demonstration circuits providing a convenient way to interface demonstration circuits with SPI or I²C buses with a PC. Up to sixteen LTC4259As, with their own distinct I²C address, can be connected in parallel to the bus, allowing for up to 64 controlled channels. The LTC4259A includes an open drain /INT output to drive an Interrupt line for fault detection without the need for software polling. Also powered off of the 3.3V supply is a sine wave oscillator using the LT1498 dual op-amp to generate the 105Hz AC signal required for AC disconnect.