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Posted on 25 February 2019

Pushing the PoE Envelope

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New requirements will demand triple the power of the current standard

Advances in Powered Device (PD) energy management ICs are enabling implementation of Power-over-Ethernet (PoE) devices requiring up to 90W.

By James Ashe, VP of Marketing, Akros Silicon Inc.

Power-over-Ethernet (PoE), like many design innovations, was developed to solve a problem: Voice-over-Internet-Protocol (VoIP) phones needed a reliable power source, and powering the phones over the Ethernet cable would eliminate the need for wall adaptors. In response, Cisco Systems pioneered PoE technology in 2000, and in June, 2003, the IEEE 802.3af standard was published. This first PoE standard allowed for PoE operation of Powered Devices (PD) up to 13 Watts and opened up a new market for PoE devices including Ethernet phones, wireless access points and security cameras. In 2009, the new IEEE 802.3at standard, sometimes referred to as PoE+, expanded the power delivery to 25.5 Watts. Both of these standards utilize one differential pair of wires in a standard Ethernet cable and RJ-45 connector.

In January 2012, Cisco published a whitepaper promoting a further advance to PoE that supports up to 60 Watts. This new configuration utilizes two differential pairs in a Cat 5 or Cat 6 cable and RJ-45 to deliver power to the PD. At this increased power level, PoE is now practical for a whole range of devices including thin clients, monitors, IPTV, building management systems, industrial networking and a host of other higher power applications. And just as the “af” standard evolved to “at,” there are already many applications that require up to 90W, making a range of new candidates for deploying higher-power PoE.

Implementation of 60W/90W PoE

Implementation of advanced PoE systems will require the availability of Power Sourcing Equipment (PSE) that is capable of delivering 60W or even 90W of power, as well as an effective technology solution for PD product manufacturers to incorporate into their new designs.

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, ultra-low 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 – minimizing radiative and conductive emission noise from the power supplies.

Total Energy Management

The system designers’ challenge is to achieve all necessary design requirements by providing an implementation that has the highest system efficiency, is adaptable, occupies the smallest possible PCB real estate, and is cost effective.

Akros Silicon recently introduced the AS1860 (Figure 1), the latest member of the company’s family of system-on-a-chip (SoC) energy management ICs that offer PD designers an integrated solution to 60W/90W PoE implementation. The device utilizes Akros’ GreenEdge™ technology that provides 2KV of digital isolation without the use of optocouplers and their associated compensation networks.

Akros’ AS1860 SoC IC enables 60W/90W PoE implementation.

In order to achieve the requirements listed above for PoE implementation in Power Devices 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.

Alternative approaches to higher power (60W and above) PoE deployments 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. In contrast, Akros’ approach can accommodate 60W and above PoE applications using just two components: one AS1860 SoC and one external FET. Moreover, by integrating GreenEdge digital isolation, the AS1860 enables the implementation of many advanced diagnostic and high-voltage telemetry features that allow operators to remotely manage power, which in turn enhances reliability and energy efficiency.

PSE – PD Interoperability

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, 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 of Broadcom’s PoE PSE controller (BCM59111) and Akros’ SoC IC www.akrossilicon.com (AS860)

Conclusion

As Ethernet bandwidths continue to increase, the nature of the devices that will require PoE will also increase. With bandwidths supporting IPTV, Point-of-Sale Terminals and other such devices, the need to manage system power will become even more important. Power Sourcing Equipment power requirements 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. The total energy management approach presented in this article provides a proven and costeffective means of responding to the evolving – and increasing – demands of PoE systems.

 

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