Power by Linear™/Analog Devices’ LT4275 and LT4276 are IEEE 802.3 and LTPoE++ powered device (PD) controllers. The LT4275A employs a proprietary LTPoE++ classification scheme, delivering 38.7 W, 52.7 W, 70 W, or 90 W of power at the PD RJ45 connector. The LT4275A is fully compatible with IEEE 802.3. The LT4275B is an IEEE 802.3at compliant, type 2 (PoE+) PD delivering up to 25.5 W. The LT4275C is an IEEE 802.3af compliant, type 1 (PoE) PD delivering up to 13 W.

The LT4275 internal charge pump provides an N-channel MOSFET solution, eliminating a larger and costlier P-channel MOSFET. A low R_DS(ON) MOSFET also maximizes power delivery and efficiency, reduces power and heat dissipation, and eases thermal design. Startup inrush current is adjustable with an external capacitor. The LT4275 also includes a power good output, on-board signature resistor, undervoltage lockout, and thermal protection. The LT4275A/LT4275B drives a single optocoupler to indicate the power level of the attached PSE. Pin-selectable support for non-standard low voltage operation is provided. Auxiliary power override is supported with the AUX pin.

The LT4276 includes an isolated switching regulator controller capable of synchronous operation in both forward and flyback topologies with auxiliary power support. The LT4276A employs the LTPoE++ classification scheme, receiving 38.7 W, 52.7 W, 70 W, or 90 W of power at the PD RJ45 connector, and is backward compatible with IEEE 802.3. The LT4276B is a fully 802.3at compliant, 25.5 W type 2 (PoE+) PD. The LT4276C is a fully 802.3af compliant, 13 W type 1 (PoE) PD. The LT4276 supports both forward and flyback power supply topologies, configurable for a wide range of PoE applications. The flyback topology supports no-opto feedback. Auxiliary input voltage can be accurately sensed with just a resistor divider connected to the AUX pin. The LT4276 utilizes an external, low R_DS(ON) N-channel MOSFET for the Hot Swap™ function, maximizing power delivery and efficiency, reducing heat dissipation, and easing the thermal design. The LT4275 and LT4276 are ideal for information displays, security, and wireless data systems.