LT4276AIUFD
LT4276AIUFD - LTPoE++/PoE+/PoE PD Forward/Flyback Controller | Analog Devices
The Analog Devices LT4276AIUFD is an LTPoE++/PoE+/PoE Powered Device (PD) forward/flyback controller in a 28-pin QFN (4x5) package. The LT4276A variant supports LTPoE++ classification for receiving 38.7W, 52.7W, 70W, or 90W at the PD RJ45 connector, in addition to standard 802.3at (PoE+) and 802.3af (PoE) modes. The IC integrates an isolated switching regulator controller capable of synchronous operation in both forward and flyback topologies with auxiliary power support.
A Power-over-Ethernet (PoE) Powered Device controller is a specialized power management IC that negotiates power delivery from an Ethernet switch or midspan injector and converts the 48V PoE rail into the regulated voltages required by the PD load. PoE controllers belong to the broader class of Power Management ICs (PMICs), specifically within the PMIC > Power Over Ethernet (PoE) Controllers family. They sit between the RJ45 magnetics and the downstream DC-DC converter, implementing detection, classification, inrush limiting, hot-swap FET control, and isolation handoff to a switching regulator.
Key features of the LT4276A include: integrated 100V Hot Swap FET, support for legacy high-power Mode A and Mode B operation, programmable inrush current, soft-start, and an auxiliary supply input that allows automatic takeover from a local 24V/48V supply. The auxiliary input also enables operation without the PD interface (wall-adapter mode). The forward topology is preferred for higher output power (>40W) because it transfers energy efficiently through a single primary-side switch, while the flyback topology suits lower-power PDs requiring multiple output rails.
Typical applications include high-power 802.3at/LTPoE++ powered devices such as 802.11ax Wi-Fi 6/7 access points, PTZ surveillance cameras, industrial PoE lighting, 5G small-cell radios, and digital signage. The auxiliary input makes it well suited to enterprise access points that must remain operational during PoE outages via a wall adapter. According to the manufacturer datasheet, the LT4276 family is pin-for-pin compatible, allowing designers to migrate between A/B/C variants and PoE+/LTPoE++ modes without PCB rework.
A critical design consideration is thermal management at 90W LTPoE++ power levels: the 28-QFN (4x5) package requires adequate copper pours on the PCB to dissipate the Hot Swap FET losses. Designers should also size the TVS protection on the Ethernet lines per IEEE 802.3 to withstand 6 kV surge events. The auxiliary supply input must be back-biased with a Schottky diode to prevent reverse conduction into the wall adapter during PoE operation.
This page synthesizes distributor pricing, pin-for-pin drop-in alternatives from the LT4276 family, and practical design notes not found in the manufacturer datasheet.
USD $2.28
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