Low Power Ethernet PHY Analysis

Today's society continues to develop, prompting today's buildings to become intelligent. The use of Ethernet (Institute of Electrical and Electronics Engineers 802.3) in building automation is growing, enabling smart buildings using enhanced sensors and control networks to manage environmental systems. (such as lighting and HVAC), access control, security systems, security systems, and even preventive maintenance monitoring. Newer buildings typically use building automation networks with dedicated Category 5 Enhanced (Cat5e) cabling, Ethernet switches and routers. Even existing building spaces are being retrofitted to accommodate networked sensors and controls.

Retrofitting is challenging for two reasons:

• Power needs to be provided to areas not initially configured with power.

• Installation space is limited as most retrofitted buildings were not originally designed to accommodate sensors and controls in walls, ceilings and floors.

Although many commercial and industrial buildings were originally designed to accommodate easy reconfiguration of interior spaces, sensor and controller technology that supports easy power distribution and provides small form factors makes retrofitting these buildings with Ethernet-based automation more feasible.

Meet the industry’s smallest, lowest power Ethernet PHY

Learn more about the DP83825I low-power 10-/100-Mbps Ethernet PHY transceiver.

Deploying Ethernet in building automation

The use of Ethernet in building automation is growing for several reasons.

First, as a mature network technology, it provides a complete hardware and software ecosystem, allowing engineers to quickly develop plug-and-play solutions. It lies at the foundation of the open systems interconnection model, thus enabling the use of standards-based data communications for aggregation, transmission, exchange, processing and storage.

Second, Ethernet can integrate products from different vendors, eliminating the need for proprietary interfaces.

Third, Ethernet offers faster data speeds than most existing point-to-point or bus-oriented communication protocols. This is due to three reasons:

• Many sensors operate at low data rates and therefore can be serviced by a single controller entity. The entity aggregates its slower data streams into a single high-speed data stream that is dumped onto the network, reducing the number of physical connections required to bring the data to a centralized management and operations center.

• Faster data speeds mean faster responses to events detected on the sensor side. This is critical for safety related systems (fire, smoke, CO2, gas detection, etc.), security and access control.

• Higher data rates expand the deployment of certain types of sensors - most notably cameras for surveillance. IP Network Cameras (IPNCs) replace analog-based CCTV camera technology. The technology uses analog image sensors and an analog transmission system that relies on specialized coaxial cables. IPNC generates a fully digital video stream and has a built-in network protocol engine, allowing connection to 100BASE-TX networks using Cat5e cable.

Integrated power and network

Another factor enabling wider deployment of IPNC is the expansion of the IEEE 802.3 standard to include Power over Ethernet (PoE). IEEE 802.3at-2009 and IEEE 802.3bt introduced standards that support power transmission over Cat5e. As described in the standard, Alternative A uses active data pairs to transmit power, while Alternative B uses backup twisted pairs, thus separating data and power.

Most IPNC currently uses 100BASE-TX. It uses two pairs of Cat5e twisted pairs, leaving a spare twisted pair for power. The standard defines two entities located at each end of the cable. The power supply equipment (PSE) is responsible for delivering power to the powered device (PD) at the other end of the cable. The standard defines four different types of usage scenarios, which correspond to four levels of maximum power transfer capability. Table 1 summarizes these types.

As can be seen from the table, each type supports the limited power budget available in the PD. Therefore, it is crucial to use energy-saving equipment in PSE and PD.

System example

Figure 1 shows an example building automation network using PoE. This example shows a combination of a sensor controller and IPNC connected to a network switch. And network switches are also power injectors. In standardized language, it is PSE. The sensor controller and IPNC on the other end of the link are PDs. Incorporate the physical layer (PHY) in each PD to handle Ethernet communications.

Given that PoE is designed to enable sensors (such as IPNC) to be deployed in locations where power may not be available or difficult to configure, the PHY consumes as little of the power budget as possible. As can be seen from Table 1, the power budget of the Type 1 PoE link at the PD side is 12.95 W. There are some losses in the power conversion and conditioning module, making less than 12.95 W available to the application circuit. The PHY should consume only a few hundred milliwatts or less, leaving most of the power for the sensor node or IPNC.

The DP83825I10-/100-Ethernet PHY provides a compact, low-power connectivity solution for building automation components such as sensor controllers, lighting controllers and IPNC. It consumes only 135 mW at 100 Mbps and is available in a 24-pin, 3 mm × 3 mm, quad flat leadless package, making it the industry's smallest 10/100 PHY. The DP83825I features media-dependent interfaces and integrated termination resistors in the media access control (MAC) interface, as well as a low pin count that reduces the media-independent interface on the MAC, allowing system designers to implement small solutions and allocate more board space and applications circuit power supply. The above is the profound impact of low-power Ethernet PHY on building automation. I hope it can give you some inspiration.