Analog Devices Inc. LT4275AIMS#PBF

Overview

LT4275AIMS#PBF from Analog Devices (formerly Linear Technology) is an IEEE 802.3af/at and LTPoE++ compliant powered device (PD) controller in a 10-lead MSOP package, supporting up to 90W delivered power at the RJ45 connector, featuring integrated signature resistor, programmable auxiliary supply override, and N-channel MOSFET gate drive for high-efficiency hot-swap control in outdoor security cameras and commercial displays.

For engineers reviewing the LT4275AIMS#PBF datasheet, LT4275AIMS#PBF pinout, LT4275AIMS#PBF application, or LT4275AIMS#PBF equivalent, this page delivers verified specifications, thermal protection behavior, LTPoE++ classification resistor mapping, and real-world PoE interface design constraints - all confirmed against the official LT4275A datasheet and package drawings.

Technical Context

The LT4275AIMS#PBF implements dual-mode classification logic: standard IEEE 802.3af (13W) and 802.3at (25.5W) via RCLASS pin, plus extended LTPoE++ (38.7W–90W) using both RCLASS and RCLASS++ pins. It uses an internal charge pump to drive an external N-channel MOSFET, eliminating P-channel FETs while maintaining 100V absolute maximum VPORT rating and –40°C to 85°C operating junction temperature range.

Its T2P open-drain output signals PSE type (floating for Type 1, pulsed at 690–990 Hz for LTPoE++, low for Type 2), while PWRGD remains low until HSGATE reaches ~7V above HSSRC - enabling precise inrush control via external CGATE capacitor and coordinated isolated supply startup.

Key Specifications

Pinout & Package

LT4275AIMS#PBF is housed in a 10-lead plastic MSOP package (3mm × 3mm footprint, 0.5mm pitch), with exposed pad not present (unlike DFN variants). All pins are surface-mount compatible and require standard reflow profiles per JEDEC J-STD-020.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar powered device controller applications.

Compared with LTC4265 and LT4275BIMS#PBF, the LT4275AIMS#PBF uniquely enables 90W LTPoE++ operation in the same MSOP footprint while retaining full IEEE 802.3af/at compatibility - making it the only option for next-gen high-power edge devices requiring backward interoperability.

Availability

LT4275AIMS#PBF is available at Aetrix Electronics and suitable for high-power wireless data systems, outdoor security camera equipment, and commercial digital signage displays requiring stable component supply, long-term lifecycle assurance, and traceable sourcing from authorized channels.

Supply support for LT4275AIMS#PBF includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

Analog Devices acquired Linear Technology in 2017 and maintains full technical and manufacturing continuity for the LT product line, including rigorous AEC-Q200-aligned reliability testing and automotive-grade process controls.

The LT4275 family was designed specifically for Power over Ethernet powered device interfaces demanding interoperability across IEEE 802.3af/at and proprietary LTPoE++ standards - targeting high-reliability infrastructure endpoints where thermal resilience and auxiliary power flexibility are critical.

FAQ

What is the maximum power level supported by the LT4275AIMS#PBF?

The LT4275AIMS#PBF supports up to 90W delivered power at the PD RJ45 connector when used with an LTPoE++-capable PSE and configured with appropriate RCLASS and RCLASS++ resistors per Table 1. This is the highest power level in the LT4275 family and exceeds IEEE 802.3at's 25.5W limit while maintaining full backward compatibility with 802.3af and 802.3at PSEs. The LT4275AIMS#PBF achieves this through dual-resistor classification signaling and robust 100V absolute maximum VPORT rating.

Does the LT4275AIMS#PBF require an external MOSFET, and why?

Yes, the LT4275AIMS#PBF requires an external N-channel MOSFET connected between VPORT (drain), HSSRC (source), and HSGATE (gate). It does not integrate a power switch. This architecture enables selection of ultra-low RDS(ON) FETs (e.g., FDMC86102) to maximize power delivery efficiency and minimize heat dissipation - a key advantage over integrated-switch controllers. The LT4275AIMS#PBF's internal charge pump provides the gate drive voltage needed to fully enhance the external N-FET, eliminating the need for a larger, less efficient P-channel device.

How does the AUX pin function on the LT4275AIMS#PBF?

The AUX pin on the LT4275AIMS#PBF enables auxiliary power supply override: when driven above 6.3V (VAUXT), it disconnects the signature resistor, disables classification, pulls down HSGATE to isolate the PoE path, and floats PWRGD to allow auxiliary-powered circuits to start independently. It features built-in hysteresis - sinking 4–8µA when below threshold - and supports auxiliary inputs from 9V to 60V DC or 24V AC. This functionality is confirmed in the LT4275A datasheet Section "Auxiliary Supply Override" and Figure 4.

What is the purpose of the RCLASS++ pin on the LT4275AIMS#PBF?

The RCLASS++ pin is exclusive to the LT4275A grade and enables LTPoE++ classification by forming a second programmable current path alongside RCLASS. When used with specific resistor pairs (e.g., 34.8Ω + 46.4Ω), it signals 38.7W, 52.7W, 70W, or 90W power requests to LTPoE++-capable PSEs. On LT4275B/C variants, RCLASS++ is not connected. This pin is essential for accessing the full 90W capability of the LT4275AIMS#PBF and is documented in Table 1 and the "LTPoE++ Classification" section of the datasheet.

Is the LT4275AIMS#PBF pin-compatible with other LT4275 variants?

Yes, the LT4275AIMS#PBF is pin-for-pin compatible with all other LT4275xIMS and LT4275xDD variants, including LT4275BIMS#PBF and LT4275CIMS#PBF. The 10-lead MSOP package, pin numbering, and electrical pin functions are identical across grades. Differences lie solely in internal firmware and classification logic - e.g., LT4275BIMS#PBF ignores RCLASS++ and limits to 25.5W, while LT4275AIMS#PBF fully utilizes both RCLASS and RCLASS++ for LTPoE++. This allows hardware reuse across power tiers with only resistor and firmware changes.