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Posted on 10 January 2020

60W-90W PoE Systems-Integration Opens Door to Energy Savings

 

 

 

Advanced PoE products requiring up to three times the power of previous-generation devices can be implemented with intelligent power management ICs

By Faisal Ahmed, Vice President, Marketing, Akros Silicon

Evolving PoE Standards

In 2011 Cisco introduced a new 60W implementation it calls UPOE while the IEEE is working on a new standard called PoE++ that specifies 60W - with potential increases to 90W - of power that can be delivered over the standard Ethernet Cat6 cable / RJ-45 connector scheme. This evolution in PoE represents significant increases from Cisco's original 7W "Inline Power" standard introduced in 2000, or even the latest 2009 PoE+ (IEEE 802.3at-2009) that allows for up to 25.5W of power delivery.

PoE++ will make it possible to power an exceptionally wide range of products, such as thin clients, IPTVs, IP turrets, remotely controlled video cameras, point of sale (POS) terminals, as well other devices that currently require a separate power source. But perhaps the most important benefit of 60-90W PoE is the ability to intelligently manage energy consumption over the enterprise through careful system integration. By utilizing energy-management ICs in each Powered Device (PD), the Power Sourcing Equipment (PSE) can modulate the power delivered on a node-by-node basis, therefore enabling a far more efficient use of the PSE power supply. And as more and higher power devices are added to the PoE network, intelligent energy management will become more important.

Managing Higher-Power PoE

The typical implementation of 15W PoE (IEEE 802.3af) and 30W PoE+ (IEE 802.3at) delivers power from the power sourcing equipment to the powered devices using two of the four twisted pairs in a standard Cat 5e or Cat 6 cable. Two variations of this scheme are possible. In the most common implementation scheme, power is superimposed on the signal pairs (Figure 1a); in the other, the spare pairs are used to deliver power (Figure 1b). In either case, the PSE provides nominal 48V of DC common-mode power of either polarity to the PD. Each PD extracts the power using a diode bridge to deliver the power to the power conversion circuitry.

Standard configurations for PoE and PoE+

The higher-power (60W-90W) PoE utilizes all four pairs in the cable to provide power. The PSE has two separate power supplies, each capable of delivering 30W-45W of power to any PD node. The two parallel power sources are then applied through two diode bridges as input sources to the PD power management (Figure 1c).

Dual power source delivery for 60-90W PoE requires use of all four pairs of wires in Ethernet cable

This power delivery system greatly expands the range of devices that can be added to the network. The PSE will now have devices that require only a few Watts of power (e.g., IP phones, access control nodes) and medium-power devices (e.g., IP security cameras, wireless access points), as well as higher-power devices like IPs TVs, POS terminals and thin client computers. With this broad range of power requirements, it now becomes all the more important for designers to manage the PSE power output delivered to each node. Questions they need to consider include:

  • What is the maximum power required at each node in the network?
  • What are the power losses in the cable to each node?
  • Is the PD operating on a continuous basis or can it be on standby at times?

If the PSE is required to supply the maximum power to each port on a continuous basis, the size of the PSE power supply would have to be considerably larger than needed under most operating conditions. The capability of delivering power to each PD at the level required, and only when required, has the dual benefit of reducing the size of the PSE power supply and allow the supply to operate at levels closer to peak efficiency.

60W/90W PoE Systems

The implementation of advanced 60-90W PoE systems will require the availability of power sourcing equipment that is capable of delivering 60W or even 90W of power, as well as an effective technology solution for power device product manufacturers to incorporate into their new designs.

In order to achieve the requirements listed above for PoE implementation of PDs at these higher power levels, a total energy management approach is needed that not only provides high-efficiency power conversion ICs, but also focuses on total system efficiency. The objective is to dynamically control the power by monitoring the environment resulting in truly efficient system designs - not just of power sub-conversion. Additionally, a total energy management approach minimizes emissions, systematically, at the source.

60W/90W PoE implementation at the PD needs to take into consideration a number of important factors:

  • Multi-rail power conversion configurable to voltages required for device sub-systems including LED backlighting.
  • Real-time energy monitoring - such as input power measurements, power system health monitoring on a continuous basis.
  • High-efficiency conversion - including light load management, ultralow standby power and sleep-mode power.
  • Fast system dynamic response and sequencing control - including the ability to rapidly change operating mode of the device from continuous to discontinuous modes and to rapidly go in and out of standby and sleep modes; flexible sequencing control to optimize multiple-rail output power start-up.
  • Digital power control - such as voltage margining to manage power consumption under differing performance requirements, managing standby and sleep requirements.
  • High-efficiency EMI control and mitigation that minimizes radiative and conductive emission noise from the power supplies.

As this list suggests, intelligent energy management takes advantage of the ability of the PSE and PDs to communicate with each other to operate the network at optimum efficiency. This requires the integration of a large number of functions including power conversion, isolation, communications and control. Integrated system-on-a-chip (SoC) solutions are becoming available handle all or most of these requirements; and without an SoC solution higher-power (60W and above) PoE PDs would require multiple components, such as two or three power management ICs, several optocouplers and custom transformers. In addition to adding component cost, consuming board space and increasing design complexity, these approaches are vulnerable to shoot-through issues and losses due to rectifier diode and reverse recovery.

An example of total power management approach that accommodates 60W-and-above PoE applications has been developed by Akros Silicon. This SoC solution uses just two components: one AS1860 SoC and one external FET. Moreover, by integrating the company's GreenEdge digital isolation technology, the AS1860 enables the implementation of many advanced diagnostic and highvoltage telemetry features that allow operators to remotely manage power, which in turn enhances reliability and energy efficiency.

Interoperability of PSEs and PDs

The IEEE has instituted a working group to establish a new PoE standard for the rapidly approaching higher-wattage implementation. In the meantime, it will be important for designers to be assured of interoperability between PSE and PD implementation. Recognizing this, Akros has entered into an interoperability collaboration with Broadcom, a leading producer of PoE PSE power controllers. Broadcom's model BCM59111 and Akros Silicon's AS1860 (Figure 2) interoperability was demonstrated at electronica 2012 in November, 2012.

Interoperability is a key factor in achieving intelligent energy management. Communications between the PSE power management controller and each PD provides information, including instantaneous load requirements, cable losses, system status and other operational data. The AS1860 SoC includes I/O functions, integral A-to-D converter and on-board digital isolation that combine to provide seamless data communications with the PSE.

Interoperability of Broadcom's PoE PSE controller (BCM59111) and Akros' SoC IC (AS860)

Summary

As Ethernet bandwidths continue to increase, the nature of the devices that will require PoE will also increase. With bandwidths supporting IPTVs, POS terminals and other such devices, the need to manage system power will become even more important. The power requirement for power sourcing equipment will be managed by having the ability to adjust the power delivered to the powered devices under widely varying operating conditions. The PDs will be required to provide this information in real time and respond to PSE control inputs. A total energy management approach can provide a flexible, cost-effective means of responding to the evolving - and increasing - demands of PoE systems.

 

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