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LTC9111

Rev. 0

For more information www.analog.com

OPERATION

PRODUCT OVERVIEW

The LTC9111 is the world’s first IEEE 802.3cg compliant

PD controller. It presents a valid wakeup signature to the

PSE in order to request power. It also supports the Serial

Communication Classification Protocol (SCCP) to com-

municates the configured voltage and current levels to the

PSE during classification. The LTC9111 monitors the port

voltage to control inrush and enable/disable the applica-

tion appropriately and safely. The LTC9111 is designed

to implement a Type E PD, compliant with a 10Base-T1L

PHY. The LTC9111 does not support the optional feature

of cable resistance measurement.

LTC9111 implements the necessary circuitry to imple-

ment an IEEE 802.3cg compliant PD design. The appli-

cation circuit of the LTC9111 uses external MOSFETs to

minimize power loss, optimize system cost, and improve

fault tolerance.

The IEEE 802.3cg mandated polarity insensitivity require-

ment is addressed using low-side rectifying MOSFETs.

External diodes are required for high-side polarity cor-

rection and back-feed prevention. The LTC9111 monitors

the unrectified voltage for classification and state naviga-

tion. Input polarity is sensed and rectified automatically.

The LTC9111 drives a pair of external MOSFETs when

transmitting a logic low during classification, regardless

of the input polarity. An external high-side MOSFET is

used to isolate the load circuitry and capacitance from the

PD Power Interface (PI); this allows system designers to

overcome restrictions imposed by the standard.

TECHNOLOGY OVERVIEW

Power over Data Lines, or PoDL, is a standard protocol

for sending DC power over two-wire copper Ethernet data

cables. PoDL is similar in concept to traditional Power

over Ethernet (PoE) but differs significantly in definition

and implementation. The differences stem mainly from

the unique power coupling techniques used in a two-

wire powering circuit, as opposed to PoE’s four and eight

wire, pair-oriented powering techniques. PoDL enables

the simultaneous transmission of power and data over

a single conductor pair, e.g., balanced twisted pair or

coaxial cable. Figure 1 illustrates one possible PoDL

circuit architecture.

VBAT

PHY

MDI/PI

LINK SEGMENT

PSE

4297 F01

Figure 1. Basic PoDL Circuit Architecture

IEEE 802.3bu (PoDL) was ratified in 2016. Multiple com-

plementary data standards are already ratified or are in

development, ranging from 10Mbps to 10Gbps and higher.

IEEE 802.3bu defines protocols for detecting, classifying,

powering, disconnecting, and standby power operation.

In 2019, the IEEE extended the PoDL standard (802.3cg)

to accommodate long reach protocol 10Base-T1L, with

cable lengths of up to 1km.

The Ethernet Alliance adopted a family of standard Power

over Ethernet acronyms to differentiate the types and gen-

erations of PoE. As such, Single-Pair Power over Ethernet

is referred to as SPoE and is a common name for 802.3cg

technology. PoDL refers to Clause 104 in 802.3 standard.

The IEEE standard also defines PoDL terminology. A device

that provides power to the network is known as power

sourcing equipment, or PSE. A device that draws power

from the network is known as a powered device, or PD.

PoDL BASICS

Common xBase-T1 Ethernet data connections consist of

a single pair of wires, AC coupled at each end to avoid

ground loops. Unlike PoE systems that transmit power

common mode to the data, PoDL systems duplex power

and data over a single pair of cables. IEEE 802.3cg defines

the classification-based power delivery protocol for the

PSE and PD. The classification protocol is defined to

ensure PSE and PD class compatibility and to avoid apply-

ing power into a short circuits, open circuits, or incom-

patible Ethernet equipment.

Upon connection to a PD, a PSE performs detection/clas-

sification before applying full operating voltage to the PD.

During classification, the PSE communicates with the PD

to request information such as the PD Class, the PD Type,

and cable resistance measurement support. Based on

cable resistance and available power, a PSE and PD nego-

tiate allocation of power to the PD. If the PSE determines

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