LTC9105

RECOMMENDED FOR NEW DESIGNS

IEEE 802.3bt PD with Telemetry and Power Priority

Data Sheet (Rev. A) Product Selection Table

Part Models: 2
1ku List Price: Starting From $2.72

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Overview

IEEE 802.3bt Powered Device (PD) Controller
400kHz I²C Interface
Continuous Voltage, Current, and Power Telemetry
Dedicated 14-Bit Delta-Sigma Current and Voltage ADCs
Automatic Maintain Power Signature (MPS)
Supports Up to 90W PDs with Extended Power
5-Event Classification Sensing with PSE Allocated Power Readback

Seamless Switchover between Dual PD or PD/AUX Inputs
Superior Surge Robustness (100V Absolute Maximum)
Wide Junction Temperature Range (-40⁰C to 125⁰C)
External Hot Swap N-Channel MOSFET for Lowest Power Dissipation and Highest System Efficiency
50mΩ Current Sense Resistor
Auxiliary Input Sense with Standby Modes
20-Pin 5mm x 5mm QFN Package

The LTC9105 is an IEEE 802.3af/at/bt ("PoE 2") Power over Ethernet (PoE) powered device (PD) controller with input current, voltage, and power telemetry. The LTC9105 includes an I²C interface to read telemetry, power sourcing equipment (PSE) allocated power, and auxiliary input status, and to write power input priority. The LTC9105 also features a configurable downstream power-up disable with under-power indication when the PSE allocated power is less than the PD requested power.

The LTC9105 utilizes an external, low R_DS(ON), N-Channel, Hot Swap MOSFET, and a 50mΩ current sense resistor, and supports the LT4321 ideal bridge to extend the end-to-end power delivery efficiency. Also included are a power good output, external signature resistor, resistor programmable classification and pin-configurable PD requested Class. The presence of an auxiliary power supply is sensed at the AUX pin and reported through the I²C interface. Automatic maintain power signature (MPS) circuitry keeps the PD interface powered when downstream current draw falls below an internal MPS threshold.

Two dedicated Delta-Sigma ADCs continuously measure PD controller input voltage and current with a typical conversion time of 100ms and with 14-bit resolution. Simultaneous conversion of current and voltage measurements enables high-accuracy power calculations.

Part Models: 2
1ku List Price: Starting From $2.72

Documentation

Data Sheet 1

LTC9105: IEEE 802.3bt PD with Telemetry and Power Priority Data Sheet (Rev.A) 03/03/2025

User Guide 1

EVAL-LTC9105-AZ User Guide: LTC9105, MAX5974C, LT4321, and ADuM1252 IEEE 802.3bt Powered Device with I2C Telemetry (Rev.0) 03/03/2025

ADI has always placed the highest emphasis on delivering products that meet the maximum levels of quality and reliability. We achieve this by incorporating quality and reliability checks in every scope of product and process design, and in the manufacturing process as well. "Zero defects" for shipped products is always our goal. View our quality and reliability program and certifications for more information.

Part Model	Pin/Package Drawing	Documentation	CAD Symbols, Footprints, and 3D Models
LTC9105ATP+	20L, THIN QFN, 5X5X0.75	Material Declaration Reliablity Data Package Resources	Ultra Librarian SamacSys
LTC9105ATP+T	20L, THIN QFN, 5X5X0.75	Material Declaration Reliablity Data Package Resources	Ultra Librarian SamacSys

This is the most up-to-date revision of the Data Sheet.

Software Resources

Evaluation Software 1

C API Documentation

The C API Documentation for this PD may be requested from the Software Request Form (SRF). This C API Documentation describes the I²C interface and programming details for the respective PD controller.

C API Documentation

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Evaluation Kits

EVAL-LTC9105-AZ: LTC9105, MAX5974C, LT4321, and ADuM1252 IEEE 802.3bt Powered Device with I2C Telemetry

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Features and Benefits

IEEE 802.3bt-compliant Class 6 PD
Port telemetry with an isolated I²C interface
5V/9.2A isolated synchronous forward converter

Product Details

The EVAL-LTC9105-AZ is an IEEE 802.3bt-compliant Type 3, Class 6 Power over Ethernet (PoE) powered device (PD) with port telemetry via I²C. The evaluation board features the LTC9105 PD interface controller, MAX5974C switching regulator controller, the LT4321 PoE ideal diode bridge controller, and the ADuM1252 I²C isolator.

The LTC9105 provides IEEE 802.3af-, IEEE 802.3at-, and IEEE 802.3bt-compliant interfacing with port voltage and current telemetry via I²C. It utilizes an external, low channel resistance, R_DS(ON) (34mΩ typical), N-channel, hot-swap metal-oxide semiconductor, field-effect transistor (MOSFET), and 50mΩ sense resistor. Automatic maintain power signature (MPS) keeps the port connected when the current drops to a low level.

The MAX5974C controls a DC/DC converter utilizing a highly efficient active-clamp forward converter topology with synchronous rectification and provides an isolated 5V/9.2A output. The LT4321 controls eight low R_DS(ON) (57mΩ typical), N-channel MOSFETs to further improve end-to-end power delivery efficiency and ease thermal design. The ADuM1252 isolates I²C data between the LTC9105 and a host controller on a nonisolated ground domain.

The EVAL-LTC9105-AZ is configured as a Class 6 PD and accepts up to 51W of delivered power from a power sourcing equipment (PSE) via its RJ45 connector (J1). The EVAL-LTC9105-AZ can be powered by a local 55V DC power supply using the auxiliary supply input terminals. With the DC590B I²C interface board connected to the EVAL-LTC9105-AZ, the EVAL-LTC9105-AZ graphical user interface (GUI) displays port telemetry and configuration options.