What Is an RJ45 Port on a PCB?

Ever since the introduction of Ethernet, the RJ-45 port (or RJ-45 jack) has become the standard for connecting wired LANs in commercial settings. When used on PCBs and in panel-mount versions, these connectors come in two common formats: magjack and non-magjack, and there are some specialized connector options that provide superior ingress protection ratings. While a common usage is in home networking equipment, today, it's common to see an Ethernet connector alongside a fiber connector in embedded devices, rack-mount computers, and single-board computers.

Types of RJ-45 Ports

Not all RJ-45 ports are created equal. Depending on your project's needs, you might encounter various types, each with features that suit a particular environment or application. Below, we'll take a look at some of the most common types.

1. Single RJ-45 Port

The RJ-45 female connector (a.k.a., RJ-45 jack) is designed to receive an RJ-45 male plug on an Ethernet cable. These connectors are used when a device only needs a single Ethernet port or a small number of Ethernet ports. These devices can be unshielded and will have a plastic casing, which means they cannot provide a connection to a shielded Ethernet cable. Shielded connectors are also available, which can connect to a shielded cable or to the chassis inside a device.

2. RJ-45 Multi-Port Jacks

Many networking devices will have groups of ports bundled together in a single component. These multi-port jacks are most often magjacks that mount to a PCB as through-hole components and contain indicator LEDs for each port. Multi-port jacks can generally support Gbps data rates (1000Base-T).

RJ-45 Port Termination

Those who are familiar with Ethernet design or with Ethernet standards will know that Ethernet Rx and Tx lanes must be terminated somewhere on the PCB before a connection is made to the RJ-45 port. The termination is performed with a set of magnetic chokes and coupled inductors, as well as a resistor network on the output side of the termination circuit. This is called""Bob Smith terminatio"" and it provides galvanic isolation, common-mode noise suppression, and impedance matching to the RJ-45 port and cable.

The magnetics termination circuit could be built from discrete components, particularly through the use of an ethernet transformer and ethernet common-mode choke. However, many RJ-45 ports today include the magnetics termination circuit built into the connector, known as a magjack connector. To locate these connectors, make sure to search for RJ-45 magjack on Octopart.

Note that gigabit Ethernet interfaces will use 4 pairs of signals and will fill up all of the pins on the RJ-45 port. This will result in the above diagram having 4 magnetics termination circuits instead of 2.

Because the termination circuit enforces galvanic isolation, the grounding scheme is typically designed with a chassis ground and a system ground. Getting this incorrect can create an EMC failure, either due to ESD testing failure or radiated emissions. To learn more about magnetics termination and the required grounding strategy in each case, read this article on Altium Resources.

RJ-45 Ports on the PCB

When wiring an RJ-45 port on the end of an Ethernet cable, there are two standard schemes to follow: T568A and T568B. Each is used for different purposes, but the main difference lies in how the wires are paired. RJ-45 ports on the PCB will have a pinout that is totally independent of the use of a T568A or T568B scheme. For example, if you look in an RJ-45 magjack datasheet, you will see a diagram that shows the cable pin numbering linkage to the PCB pin numbering across the magnetics termination circuit.

In addition, on shielded RJ-45 ports, there could be another 4 pins to power the two LEDs on the sides of the connector body. These LEDs should receive power from the system GND side of the termination circuit. An example for the JX0026D21NL from Pulse is shown below.

Where You'll Find RJ-45 Ports

From homes to industrial environments, RJ-45 ports are essential in maintaining stable communication between devices.Let'ss explore some of their most common uses.

1. Embedded Computing

Many embedded devices forego the use of wireless networking in favor of wired networking over copper or fiber. High-compute embedded devices that are part of a larger network may feature RJ-45 for copper connections and an SFP transceiver receptacle for fiber connections.

2. Data Centers

Data centers rely heavily on wired and optical connections to maintain high-speed data transmission across servers and storage systems. RJ-45 ports and Ethernet cabling are used for shorter distance, lower bandwidth links, while higher-speed, longer-distance links will use optical fiber or active copper interconnects (e.g., over twinax cabling) for interconnects between server clusters requiring much greater processing and computing.

3. Industrial Applications

In manufacturing, energy, automation, and other industrial settings, shielded RJ-45 ports are used for data transmission between production and computing assets. These connectors may be rugged versions of panel-mount connectors with high IP ratings to ensure they can withstand ingress and mechanical damage.

4. Home Networking

RJ-45 ports are just as important in home networking. Computers, routers, and modems all typically use unshielded RJ-45 ports as a low-cost solution for connecting devices. Because these systems typically are built from plastic and do not have an earth connection or chassis GND, they do not need to use a shielded RJ-45 port.

Compare & Find RJ-45 Ports for Your PCB

Connectors, cabling, panel-mount receptacles, and more... Octopart makes your search a snap with a platform that lets you explore a vast inventory of RJ-45 ports, cables and wires, and other components from authorized distributors. Easily compare options, check real-time availability, and find the perfect electronic components for your project today!

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FAQs About RJ-45 Ports

Below, we've addressed some additional questions concerning RJ-45 ports. Explore additional FAQs, then compare RJ-45 ports at Octopart.com to determine which will best suit your needs. 

Can an RJ-45 port be used for PoE (Power over Ethernet)?

The standard RJ-45 ports used on Ethernet cables can be used for PoE, but a PoE-compatible RJ45 port must be used on the PCB. Power over Ethernet enables data and electrical power to transmit over a single Ethernet cable, which eliminates the need for separate power sources for network devices like IP cameras, VoIP phones, and wireless access points. Many modern RJ-45 ports, especially those used in Cat6 or higher cabling, are PoE-compatible, but only if the receptacle on the PCB is designed to work with PoE.

What is the difference between a shielded and unshielded RJ-45 port?

A shielded RJ-45 port is assembled with a metal housing that protects against electromagnetic interference (EMI). The use of metal housing connectors is standard in systems that have a metal chassis, as the metal shielding can be connected to the chassis GND. This allows a shielded Ethernet cable to be used, although one should note that the shielding needs to be connected to the chassis and/or system GND at each end of the link to provide any shielding against EMI without also causing a new conducted or radiated emissions problem.

Can I use an RJ-45 port for non-Ethernet applications?

Although RJ-45 ports are primarily used for Ethernet networking, they can also be used in non-Ethernet applications such as serial communication, telecommunications, or custom cable configurations. However, depending on the application, these use cases may require different wiring arrangements or adapters. For example, rack-mount networking switches and routers can include a serial port (RS232) over an unterminated (non-magjack) RJ45 port. Be careful with this usage because the output on these cables is typically unfiltered, and any common mode noise on the cable could result in an EMC testing failure.