PSE Power Interface (PSE PI) Documentation

The Power Sourcing Equipment Power Interface (PSE PI) plays a pivotal role in the architecture of Power over Ethernet (PoE) systems. It is essentially a blueprint that outlines how one or multiple power sources are connected to the eight-pin modular jack, commonly known as the Ethernet RJ45 port. This connection scheme is crucial for enabling the delivery of power alongside data over Ethernet cables.

Documentation and Standards

The IEEE 802.3 standard provides detailed documentation on the PSE PI. Specifically:

  • Section “33.2.3 PI pin assignments” covers the pin assignments for PoE systems that utilize two pairs for power delivery.

  • Section “145.2.4 PSE PI” addresses the configuration for PoE systems that deliver power over all four pairs of an Ethernet cable.

PSE PI and Single Pair Ethernet

Single Pair Ethernet (SPE) represents a different approach to Ethernet connectivity, utilizing just one pair of conductors for both data and power transmission. Unlike the configurations detailed in the PSE PI for standard Ethernet, which can involve multiple power sourcing arrangements across four or two pairs of wires, SPE operates on a simpler model due to its single-pair design. As a result, the complexities of choosing between alternative pin assignments for power delivery, as described in the PSE PI for multi-pair Ethernet, are not applicable to SPE.

Understanding PSE PI

The Power Sourcing Equipment Power Interface (PSE PI) is a framework defining how Power Sourcing Equipment (PSE) delivers power to Powered Devices (PDs) over Ethernet cables. It details two main configurations for power delivery, known as Alternative A and Alternative B, which are distinguished not only by their method of power transmission but also by the implications for polarity and data transmission direction.

Alternative A and B Overview

  • Alternative A: Utilizes RJ45 conductors 1, 2, 3 and 6. In either case of networks 10/100BaseT or 1G/2G/5G/10GBaseT, the pairs used are carrying data. The power delivery’s polarity in this alternative can vary based on the MDI (Medium Dependent Interface) or MDI-X (Medium Dependent Interface Crossover) configuration.

  • Alternative B: Utilizes RJ45 conductors 4, 5, 7 and 8. In case of 10/100BaseT network the pairs used are spare pairs without data and are less influenced by data transmission direction. This is not the case for 1G/2G/5G/10GBaseT network. Alternative B includes two configurations with different polarities, known as variant X and variant S, to accommodate different network requirements and device specifications.

Table 145-3 PSE Pinout Alternatives

The following table outlines the pin configurations for both Alternative A and Alternative B.

Conductor
Alternative A

(MDI-X)
Alternative A
Alternative B
Alternative B

1

Negative V

Positive V

2

Negative V

Positive V

3

Positive V

Negative V

4

Negative V

Positive V

5

Negative V

Positive V

6

Positive V

Negative V

7

Positive V

Negative V

8

Positive V

Negative V

Note

  • “Positive V” and “Negative V” indicate the voltage polarity for each pin.

  • “-” indicates that the pin is not used for power delivery in that specific configuration.

PSE PI compatibilities

The following table outlines the compatibility between the pinout alternative and the 1000/2.5G/5G/10GBaseT in the PSE 2 pairs connection.

Variant

Alternative (A/B)

Power Feeding Type (Direct/Phantom)

Compatibility with 1000/2.5G/5G/10GBaseT

1

A

Phantom

Yes

2

B

Phantom

Yes

3

B

Direct

No

Note

  • “Direct” indicate a variant where the power is injected directly to pairs

    without using magnetics in case of spare pairs.

  • “Phantom” indicate power path over coils/magnetics as it is done for

    Alternative A variant.

In case of PSE 4 pairs, a PSE supporting only 10/100BaseT (which mean Direct Power on pinout Alternative B) is not compatible with a 4 pairs 1000/2.5G/5G/10GBaseT.

PSE Power Interface (PSE PI) Connection Diagram

The diagram below illustrates the connection architecture between the RJ45 port, the Ethernet PHY (Physical Layer), and the PSE PI (Power Sourcing Equipment Power Interface), demonstrating how power and data are delivered simultaneously through an Ethernet cable. The RJ45 port serves as the physical interface for these connections, with each of its eight pins connected to both the Ethernet PHY for data transmission and the PSE PI for power delivery.

+--------------------------+
|                          |
|          RJ45 Port       |
|                          |
+--+--+--+--+--+--+--+--+--+                +-------------+
  1| 2| 3| 4| 5| 6| 7| 8|                   |             |
   |  |  |  |  |  |  |  o-------------------+             |
   |  |  |  |  |  |  o--|-------------------+             +<--- PSE 1
   |  |  |  |  |  o--|--|-------------------+             |
   |  |  |  |  o--|--|--|-------------------+             |
   |  |  |  o--|--|--|--|-------------------+  PSE PI     |
   |  |  o--|--|--|--|--|-------------------+             |
   |  o--|--|--|--|--|--|-------------------+             +<--- PSE 2 (optional)
   o--|--|--|--|--|--|--|-------------------+             |
   |  |  |  |  |  |  |  |                   |             |
+--+--+--+--+--+--+--+--+--+                +-------------+
|                          |
|       Ethernet PHY       |
|                          |
+--------------------------+

Simple PSE PI Configuration for Alternative A

The diagram below illustrates a straightforward PSE PI (Power Sourcing Equipment Power Interface) configuration designed to support the Alternative A setup for Power over Ethernet (PoE). This implementation is tailored to provide power delivery through the data-carrying pairs of an Ethernet cable, suitable for either MDI or MDI-X configurations, albeit supporting one variation at a time.

        +-------------+
        |    PSE PI   |
8  -----+                             +-------------+
7  -----+                    Rail 1   |
6  -----+------+----------------------+
5  -----+      |                      |
4  -----+      |             Rail 2   |  PSE 1
3  -----+------/         +------------+
2  -----+--+-------------/            |
1  -----+--/                          +-------------+
        |
        +-------------+

In this configuration:

  • Pins 1 and 2, as well as pins 3 and 6, are utilized for power delivery in addition to data transmission. This aligns with the standard wiring for 10/100BaseT Ethernet networks where these pairs are used for data.

  • Rail 1 and Rail 2 represent the positive and negative voltage rails, with Rail 1 connected to pins 1 and 2, and Rail 2 connected to pins 3 and 6. More advanced PSE PI configurations may include integrated or external switches to change the polarity of the voltage rails, allowing for compatibility with both MDI and MDI-X configurations.

More complex PSE PI configurations may include additional components, to support Alternative B, or to provide additional features such as power management, or additional power delivery capabilities such as 2-pair or 4-pair power delivery.

        +-------------+
        |    PSE PI   |
        |        +---+
8  -----+--------+   |                 +-------------+
7  -----+--------+   |       Rail 1   |
6  -----+--------+   +-----------------+
5  -----+--------+   |                |
4  -----+--------+   |       Rail 2   |  PSE 1
3  -----+--------+   +----------------+
2  -----+--------+   |                |
1  -----+--------+   |                 +-------------+
        |        +---+
        +-------------+

Device Tree Configuration: Describing PSE PI Configurations

The necessity for a separate PSE PI node in the device tree is influenced by the intricacy of the Power over Ethernet (PoE) system’s setup. Here are descriptions of both simple and complex PSE PI configurations to illustrate this decision-making process:

Simple PSE PI Configuration: In a straightforward scenario, the PSE PI setup involves a direct, one-to-one connection between a single PSE controller and an Ethernet port. This setup typically supports basic PoE functionality without the need for dynamic configuration or management of multiple power delivery modes. For such simple configurations, detailing the PSE PI within the existing PSE controller’s node may suffice, as the system does not encompass additional complexity that warrants a separate node. The primary focus here is on the clear and direct association of power delivery to a specific Ethernet port.

Complex PSE PI Configuration: Contrastingly, a complex PSE PI setup may encompass multiple PSE controllers or auxiliary circuits that collectively manage power delivery to one Ethernet port. Such configurations might support a range of PoE standards and require the capability to dynamically configure power delivery based on the operational mode (e.g., PoE2 versus PoE4) or specific requirements of connected devices. In these instances, a dedicated PSE PI node becomes essential for accurately documenting the system architecture. This node would serve to detail the interactions between different PSE controllers, the support for various PoE modes, and any additional logic required to coordinate power delivery across the network infrastructure.

Guidance:

For simple PSE setups, including PSE PI information in the PSE controller node might suffice due to the straightforward nature of these systems. However, complex configurations, involving multiple components or advanced PoE features, benefit from a dedicated PSE PI node. This method adheres to IEEE 802.3 specifications, improving documentation clarity and ensuring accurate representation of the PoE system’s complexity.

PSE PI Node: Essential Information

The PSE PI (Power Sourcing Equipment Power Interface) node in a device tree can include several key pieces of information critical for defining the power delivery capabilities and configurations of a PoE (Power over Ethernet) system. Below is a list of such information, along with explanations for their necessity and reasons why they might not be found within a PSE controller node:

  1. Powered Pairs Configuration

    • Description: Identifies the pairs used for power delivery in the Ethernet cable.

    • Necessity: Essential to ensure the correct pairs are powered according to the board’s design.

    • PSE Controller Node: Typically lacks details on physical pair usage, focusing on power regulation.

  2. Polarity of Powered Pairs

    • Description: Specifies the polarity (positive or negative) for each powered pair.

    • Necessity: Critical for safe and effective power transmission to PDs.

    • PSE Controller Node: Polarity management may exceed the standard functionalities of PSE controllers.

  3. PSE Cells Association

    • Description: Details the association of PSE cells with Ethernet ports or pairs in multi-cell configurations.

    • Necessity: Allows for optimized power resource allocation in complex systems.

    • PSE Controller Node: Controllers may not manage cell associations directly, focusing instead on power flow regulation.

  4. Support for PoE Standards

    • Description: Lists the PoE standards and configurations supported by the system.

    • Necessity: Ensures system compatibility with various PDs and adherence to industry standards.

    • PSE Controller Node: Specific capabilities may depend on the overall PSE PI design rather than the controller alone. Multiple PSE cells per PI do not necessarily imply support for multiple PoE standards.

  5. Protection Mechanisms

    • Description: Outlines additional protection mechanisms, such as overcurrent protection and thermal management.

    • Necessity: Provides extra safety and stability, complementing PSE controller protections.

    • PSE Controller Node: Some protections may be implemented via board-specific hardware or algorithms external to the controller.