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Data Sheet

LTC9101-2B/LTC9102

APPLICATIONS INFORMATION

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Rev. 0 | 18 of 39

OVERVIEW

Power over Ethernet, or PoE, is a standard protocol for sending DC

power over copper Ethernet data wiring. The IEEE group that ad-

ministers the 802.3 Ethernet data standards added PoE powering

capability in 2003. This original PoE standard, known as 802.3af,

allowed for 48V DC power at up to 13W. 802.3af was widely

popular, but 13W was not adequate for some applications. In 2009,

the IEEE released a new standard, known as 802.3at or PoE+,

increasing the voltage and current requirements to provide 25.5W

of delivered power. IEEE 802.3af and 802.3at are commonly known

as PoE 1. In 2018, the IEEE released the latest PoE standard,

known as 802.3bt or PoE 2. 802.3bt maximizes PD delivered power

at 71.3W.

The IEEE standard also defines PoE terminology. A device that

provides power to the network is known as a PSE, or power sourc-

ing equipment, while a device that draws power from the network

is known as a PD, or powered device. PSEs come in two types:

endpoints (typically network switches or routers), which provide

data and power; and midspans, which provide power but pass

through data. Midspans are typically used to add PoE capability to

existing non-PoE networks. PDs are typically IP phones, wireless

access points, security cameras, and similar devices.

PoE++ Evolution

Even during the development of the IEEE 802.3at (PoE 1) 25.5W

standard, it became clear there was a significant and increasing

need for more than 25.5W of delivered power. In 2013, the 802.3bt

task force was formed to develop a standard capable of increasing

delivered PD power.

The primary objective of the task force was to use all four pairs

of the Ethernet cable as opposed to the two pair power utilized by

802.3at. Using all four pairs allows for at least twice the delivered

power over existing Ethernet cables. Further, the amount of current

per two pairs (known as a pairset) is increased while maintaining

the Ethernet data signal integrity. 802.3bt increases PD delivered

power from 25.5W to 71.3W, enabling IEEE-compliant high power

PD applications.

The LTC9101-2B/LTC9102 is a 2-pair device, delivering power to

each port over one pairset. Each pairset is driven by a dedicated

power channel. In this data sheet, the term channel refers to the

PSE circuitry assigned to a corresponding pairset. For the purposes

of this document, the terms channel and pairset may be considered

interchangeable.

In addition, IEEE 802.3bt enables substantially lower Maintain Pow-

er Signature (MPS) currents, resulting in significantly lower standby

power consumption. This allows new and emerging government

or industry standby regulations to be met using standard PoE

components.

LTC9101-2B/LTC9102 Product Overview

The LTC9101-2B/LTC9102 is a sixth generation PSE controller that

implements up to 48 (25.5W) 2-pair PSE ports in either an endpoint

or midspan application. Virtually all necessary circuitry is included

to implement an IEEE 802.3bt-compliant PSE design, requiring

an external power MOSFET and sense resistor per port; these

minimize power loss compared to alternative designs with onboard

MOSFETs, and increase system reliability.

The LTC9101-2B/LTC9102 chipset implements an optional propriet-

ary isolation scheme for inter-chip communication. This architecture

substantially reduces BOM cost by replacing expensive opto-isola-

tors and isolated power supplies with a single low-cost transformer.

A single LTC9101-2B is capable of controlling a bus of up to 4

LTC9102s over this transformer-isolated interface. Direct connec-

tion of the LTC9101-2B and the associated LTC9102s is also

possible.

The LTC9101-2B/LTC9102 offers a configurable interrupt signal

triggered by per-port events, per-channel power on control and

fault telemetry, per-channel current monitoring, VEE monitoring, and

100ms rolling current and voltage averaging.

The LTC9101-2B/LTC9102 also offers advanced sixth-generation

PSE features including internal eFlash for storage of firmware up-

dates and custom user configuration packages, 802.3at/bt-compli-

ant mode select, I2C quad virtualization for full backwards-compati-

bility with quad-based IC drivers, ultra-low 100mΩ sense resistors,

+80V/–20V tolerant port-facing pins, and improvements to cable

surge ride through.

Each LTC9102 power channel includes dedicated detection and

classification hardware. This allows all ports and channels to detect,

classify and power on simultaneously, drastically reducing power

on latency across a switch. Other less-advanced PSEs are subject

to visible delays as PDs, e.g. LED lights, power on a port-by-port

basis.

VEE and port current measurements are performed simultaneously,

enabling coherent and precise per-port power monitoring.

802.3BT 2-PAIR OPERATION

The LTC9101-2B includes up to 12 groups of four identical chan-

nels. Each group of four channels is referred to as a quad. In the

LTC9101-2B architecture, each quad contains register configuration

and status for exactly four channels and provides control for four

2-pair 802.3bt ports.

In 2-pair mode, the IEEE 802.3bt standard supports delivered

power up to 25.5W, supporting PDs requesting Class 4 power or

lower. High-power single-signature PDs (Class 5 and above) and

dual-signature PDs are demoted to Class 4 (25.5W) power and

receive power over a single pairset.

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