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Power over Ethernet (PoE)

Power over Ethernet (PoE) technology uses data network cables to transmit electrical power to devices. This allows a single cable to provide both data connection and power to devices like Wireless Access Points (WAPs), human-machine interfaces (HMI), and a wide range of other IP-enabled devices. The principal advantage of PoE is that it makes power cables unnecessary and saves customers the cost of cabling for both data networks and electrical power.

Benefits of PoE

PoE Standards

The supply of power via a Cat-5 cable is defined in the IEEE 802.3af Power over Ethernet standard. The PoE standards used to be limited to a few watts, but newer PoE technologies enable even higher power. For example, PoE+ allows power up to 25 W per port and PoE++ (a four-pair Power over Ethernet system) ranges from 70 W to 100 W by using all of the wires of the existing cable. In parallel to this PoE standard, Analog Devices has defined the proprietary standard LTPoE++™, which defines the specifications up to 90 W powered device (PD) power (see below Table).

Featured Products of PoE Standards

PoE Standard PoE Type PD Power (W) Usable Power (W)
PoE (IEEE 802.3af) Type 1 13 11.25
PoE+ (IEEE 802.3at) Type 2 25 22
ADI’s LTPoE++ LTPoE++ 38.7 32.9
LTPoE++ 52.7 44.8
LTPoE++ 70 60.8
LTPoE++ 90 76.8

Power-over-Ethernet (PoE) Interface Controllers

Analog Devices’ power over Ethernet (PoE) products encompass a wide variety of power sourcing equipment (PSE) and powered device (PD) controllers that support multiple power levels: IEEE PoE (13W, 802.3af), IEEE PoE+ (25.5W, 802.3at), IEEE PoE++ (71.3W, 802.3bt), and ADI LTPoE++ (90W) standard. PSE and PD controllers provide complete PoE solutions and use external components such as power MOSFETs and sense resistors to lower resistance in the power path—minimizing heat dissipation and maximizing power efficiency. In addition, robust cable discharge protection scheme, a high abs max rating on all analog pins, wide operating temperature, and overtemperature protection all make for extremely rugged PoE solutions that meet IEC61000 cable discharge requirements that far exceed ESD and cable ESD testing levels.

PoE Power Sourcing Equipment (PSE)

Analog Devices power sourcing equipment (PSE) controllers support multiple power levels of power over Ethernet: IEEE PoE (13W, 802.3af), IEEE PoE+ (25.5W, 802.3at), IEEE PoE++ (71.3W, 802.3bt), and ADI LTPoE++ (90W) standard. PSE controllers are responsible for detecting and classifying powered devices (PDs), as well as sourcing the right amount of power to PDs over Ethernet cables. Latest generation PSE controllers are IEEE compliant, use 0.15 Ω sense resistors to lower power dissipation, and use a high reliability 4-point PD detection scheme to eliminate false PD detections. External MOSFETs, a scalable cable discharge protection scheme, an 80 V abs max rating on all analog pins, and overtemperature protection all ensure robust operation.

Featured Products of PoE Power Sourcing Equipment

Part Number # of Ports PoE Standard Product Description PoE Type Max Power (typ)/w
LTC4291-1 4 IEEE 802.3af, IEEE 802.3at, IEEE 802.3bt 4-Port IEEE 802.3bt PoE PSE Controller 1, 2, 3, 4 71
LTC4292 4 IEEE 802.3af, IEEE 802.3at, IEEE 802.3bt 4-Port PoE++ PSE Analog Controller 1, 2, 3, 4 71
LTC4266C 4 IEEE 802.3af Quad PoE/PoE+/LTPoE++ PSE Controller 1 13
LTC4266 4 IEEE 802.3af, IEEE 802.3at Quad IEEE 802.3at Power Over Ethernet Controller 2 25.5

PoE Powered Device (PD)

Analog Devices powered device (PD) controllers support multiple power levels of power over Ethernet: IEEE PoE (13W), IEEE PoE+ (25.5 W), IEEE PoE++ (71 W), and ADI LTPoE++ (up to 90 W) standard. PD controllers are ultimately responsible for providing the correct signature and classification to power sourcing equipment (PSE), so that PSEs source the right amount of power to PDs over the Ethernet cables. Some of the PD controllers integrate efficient dc-to-dc converters to simplify designs, while other PD controllers give designers the ability to choose their own dc-to-dc converters, which helps designers achieve unique cost-efficiency requirements.

Featured Products of PoE Powered Device

Part Number # of Ports PoE Standard Product Description PoE Type
LT4293 1 IEEE 802.3af, IEEE 802.3at, IEEE 802.3bt, LTPoE++ LTPoE++/IEEE 802.3bt PD Interface Controller 1, 2, 3, 4, LTPoE++
LT4294 1 IEEE 802.3af, IEEE 802.3at, IEEE 802.3bt IEEE 802.3bt PD Interface Controller 1, 2, 3, 4
LT4295 1 IEEE 802.3af, IEEE 802.3at, IEEE 802.3bt IEEE 802.3bt PD Interface with Forward/Flyback Controller 1, 2, 3, 4

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    Resources

    Video


    PoE++ Video Product Brief

    Video


    Next Generation Power Over Ethernet

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