LTC9105

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.