As networks become larger, the demand for power increases significantly. Ethernet is already a key part of the technology ecosystem, and the new Power over Ethernet (PoE) universal standard (IEEE 802.bt) will help enable a number of new applications by providing power up to 90 watts. PoE powered device (PD) solutions from ON Semiconductor not only support the new standard limit of power but extend it further to 100 W. This helps address the high power demand challenge for applications including connected lighting and telecommunications, with design flexibility, cost-effectiveness and energy efficiency.

What is PoE IEEE 802.3bt?

PoE is a networking feature defined by the IEEE 802.3af and 802.3at standards. PoE technology enables the transfer of power and data over Ethernet cables. The amount of power transferred is managed through the connection between the power sourcing equipment (PSE) and the PD. During this process, the PSE recognizes the type and class of PD devices based on the PoE standard and then ensures it receives the appropriate and safe amount of power.

The new universal PoE standard (IEEE 802.3bt), also referred to as “PoE 2”, was ratified in September 2018. It is backward compatible with the existing standard, but differs in two key ways:

1.Increases the possible output power the PSE can provide by using all four pairs of wiring in the PoE cable

2.Improves energy efficiency by recognizing two new types (3 and 4) and four new classes (5-8) of devices

Standard	Power - PSE output	Power - PD input	Power - Useable for application (85% efficiency)
802.3af (PoE)	15.4 W	13 W	11 W
802.3at (PoE+)	30 W	25.5 W	21.6 W
802.3bt (PoE 2)	90 W	71.3 to 90 W	21.6 W to 76.5 W

PoE-PD Solutions

The combination of rising energy costs, demands for smaller solutions, the need to comply with multiple standards and restricted budgets, has presented a number of challenges for application designers.

Using a unique high-voltage manufacturing process, ON Semiconductor has developed more advanced power conversion semiconductors that operate with high levels of efficiency and low levels of heat generation in a compact space.

There are many misconceptions when it comes to PoE. Check out our video below to understand a few common myths associated with PoE that could be holding you back from utilizing it in your designs!

 Continue watching this series by viewing part two here!

GreenBridge 2™ Quad MOSFET

A PD in a PoE application requires a bridge circuit to regulate the polarity of the input power when the PSE supplying power to the PD is equipped with an uninterruptible power supply (UPS). A simple diode bridge design has been the most popular approach to this, providing a reliable and low cost solution. However, as PDs require more power, the conduction loss of the diode bridge caused by the forward voltage drop becomes one of the main issues to be solved efficiently. ON Semiconductor’s GreenBridge solution has been developed to address this issue by reducing power losses in the bridge circuit.

Completing a design based on the FDMQ8203 GreenBridge solution simply requires the addition of external circuitry to drive and protect the MOSFETs. After testing, the GreenBridge solution reduced power loss, improved efficiency and reduced operating temperature in a solution that occupies around half the PCB area of the equivalent diode bridge, as shown in Figure 1.

Figure 1. GreenBridge™ 1 Solution vs. a Traditional Diode Bridge Solution

The IEEE 802. 3bt compliant FDMQ8205 containstwo N-channel and two P-channel 100 V-rated MOSFETs as well as all necessary gate drivers. The device requires no external circuitry to drive or protect it, while providing the lowest RDS(on). Compared to traditional diode bridge solutions, a GreenBridge solution based on FDMQ8205 provides up to 10 times better power dissipation. The overall system size is less than 1/4 of the traditional diode bridge solutions.

Figure 2. GreenBridge™ 2 solutions vs diode bridge solution

Learn more about how a Quad MOSFET approach enables more energy-efficient PoE solutions here.

1. IEEE 802.3bt Compliant PoE-PD Interface Controllers: NCP1095, NCP1096

The NCP1095 and NCP1096 PoE-PD interface controllers incorporate all required functionalities for PoE systems including detection, classification and current lighting. These devices features an external pass transistor and Autoclass support for optimized power allocation based on PD type and classification. Providing a higher level of integration, the NCP1096 features an internal hot-swap FET transistor with the lowest RDS(on) available in a Type 3 or 4 PoE controller. The NCP1095GEVB and NCP1096GEVB evaluation boards allow designers to quickly evaluate both controllers’ operation before implementing a physical design. They include the GreenBridge2 active bridge, RJ45 connectors and LAN transformer.

Figure 3. NCP1095/NCP1096 Integrated Controllers

2. 100 V N-Channel PowerTrench® MOSFET

The FDMC8622 MOSFET is developed using an advanced Power Trench® process that incorporates Shielded Gate technology. This process has been optimized for RDS(on), switching performance and ruggedness. The FDMC8622 supports high power and current handling capability and is provided in a widely used, 100% UIL Tested surface mount package.

3. DC-DC Converter

The NCP1566 is a highly integrated dual-mode active-clamp PWM controller targeting next-generation high-density, high-performance and small to medium power level isolated dc-dc converters for use in telecom and datacom industries. It can be configured in either voltage mode control with input voltage feed-forward or peak current mode control. Peak current mode control may be implemented with input voltage feedforward as well. Adjustable adaptive overlap time optimizes system efficiency based on input voltage and load conditions. This controller integrates all the necessary control and protection functions to implement an isolated active clamp forward or asymmetric half-bridge converter.

4. ESD Protection Diode

The ESD8004 is designed to protect high-speed data lines from ESD. Ultra-low capacitance and low ESD clamping voltage make this device an ideal solution for protecting voltage sensitive high-speed data lines

Why PoE?

Although wireless connections provide many significant advantages, the power and data requirements of all devices used in the technology ecosystem vary widely. There are multiple benefits to implementing PoE features and capabilities, such as:

•  Time and Cost Savings − as no power cables are needed, costs and installation time are reduced. The installation is also simplified as mains wiring regulations do not apply and a qualified electrician is not required.
•  Flexibility − proximity to a power source is no longer a consideration. Equipment can be placed wherever LAN cables can be run.
•  Reliability − The centralized power source replaces low-cost wall adapters and allows the system to be backed up by a single uninterruptible power supply.
•  Security - Offering a more robust safety and security protocol than wireless, it heightens protection against hackers.
•  Ease and Convenience - PoE can transmit power and data at the same time, reducing wiring harness, efficient and convenient.

Recap

The new PoE standard, IEEE 802.3bt, supports designers to provide PD with up to 90 W of power, opening the door to higher power applications, including connected lighting, security cameras, digital signage, telecommunications, point-of-sale (POS) terminals and satellite data networks. ON Semiconductor provides a full range of IEEE 802.3bt-compliant PoE-PD solutions, and expands the power to 100 W with a large number of reference designs and application notes to solve challenges such as energy efficiency, size, and thermal performance. Making this technology more accessible for all development engineers will help enable a greater number of connected devices with guaranteed interoperability and higher energy efficiency.