Data Sheet

LTC9105

IEEE 802.3bt PD with Telemetry and Power Priority

19-101904; Rev A; 2/25

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FEATURES

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IEEE 802.3bt Powered Device (PD) Controller

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400kHz I2C Interface

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Continuous Voltage, Current, and Power Telemetry

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Dedicated 14-Bit Delta-Sigma Current and Voltage ADCs

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Automatic Maintain Power Signature (MPS)

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Supports Up to 90W PDs with Extended Power

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5-Event Classification Sensing with PSE Allocated Power Read-

back

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Seamless Switchover between Dual PD or PD/AUX Inputs

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Superior Surge Robustness (100V Absolute Maximum)

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Wide Junction Temperature Range (-40⁰C to 125⁰C)

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External Hot Swap N-Channel MOSFET for Lowest Power Dissi-

pation and Highest System Efficiency

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50mΩ Current Sense Resistor

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Auxiliary Input Sense with Standby Modes

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20-Pin 5mm x 5mm QFN Package

APPLICATIONS

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IEEE 802.3bt PDs with Power Telemetry

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Wireless Access Points/Pico Cells

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Internet Protocol (IP) Security Cameras

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Power over Ethernet (PoE) Lighting

DESCRIPTION

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 inter-

face 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 RDS(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 ef-

ficiency. 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 con-

troller 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.

TYPICAL APPLICATION

Figure 1. LTC9105 IEEE 802.3bt Powered Device with Telemetry and I2C