introduction
With the growing popularity and sophistication of power over Ethernet, it is not surprising that PSE and PD developers are eager to follow the next wave of IEEE and begin to offer more power over Ethernet cables. However, as with many industry standards, the finalization of the IEEE PoE standard often lags far behind the market, and the latest schedule from the IEEE PoE Task Force shows that the 71W 802.3bt standard will not be ready until the beginning of 2018. From a technical point of view In terms of waiting too long, waiting so long means it's easy to miss out on business opportunities or market opportunities, so what should PSE and PD developers do in this situation? Nothing to say, of course, right now Start designing and manufacturing equipment! Developers who want to be the first to enter the 802.3bt market today are available today from ADI's LT4295 IEEE 802.3bt PD controller, which meets version 2.0 of the draft standard requirements.
The greater the power, the greater the potential
Not surprisingly, the focus of the IEEE PoE task force and developers has been on the eventual power of PDs in 2003. In 2003, the IEEE PoE Task Force specified in the original IEEE 802.3af PoE standard that RJ-45 Since then, the market continues to demand more power, so in 2009 the IEEE PoE Task Force revised its standards and released IEEE 802.3at (also known as PoE +), raising the maximum PD power level to 25.5W. To this day, it is expected that the revised draft version of IEEE 802.3bt 2.0 (also known as PoE ++ or 4PPoE), currently under development, will provide up to 71W of power for the PD.
With even greater power, developers can easily add more functionality and upgrade existing products, taking security cameras as an example, which has evolved with the PoE standard. With only 13W of power available , The initial PoE powered security camera was a simple static system.However, as 802.3at was allocated 25.5W of power, more power was available to power a wide range of embedded motors, enabling security cameras to provide up, down, left and right Mobile and zoom functions now with the ability to take advantage of the 802.3bt 71W power, security cameras with up, down, left and right movement and zoom functions can also integrate fans and heating components to support operation at extreme temperatures. In some cases, more High PoE power levels may help open new markets, for example, traditional LED lighting manufacturers may only produce ceilings with wall-mounted switches for lighting, but now they can produce PoE-enabled products that will Helps to create opportunities for smart homes or smart buildings Whether or not greater power contributes to the final product Evolution or completely changed, it is clear that every revision PoE standards have brought greater market potential.
Changes to the PSE-PD link
As you may have guessed already: 4PPoE stands for 4-Pair PoE, since the 802.3bt specification takes advantage of all 4 twisted-pair lines in an Ethernet cable for up to 100m of power transfer; in older PoE standards , 4-wire is not compatible with power delivery Figure 1 shows a typical block diagram of an IEEE 802.3bt PSE-PD link.Cable cabling requirements remain unanswered, but cable cabling committees and manufacturers are guessing that 802.3bt will require at least a Category 5E cable designed to support increased power levels and operating at 10GBASE-T (10Gbit / s Ethernet data rate) In any event, as we are now reaching the limits of the current handling of Ethernet cables, Neglected cable routing system performance characteristics.
802.3bt PSE CONTROLLER: 802.3bt PSE Controller DATA PAIR: Data Transfer Line Pair SPARE PAIR: Spare Pair Pair 802.3bt PD CONTROLLER: 802.3bt PD Controller DC / DC CONVERTER: DC / DC Converter
802.3bt introduces two new types of PD topologies: single-feature PDs, which are 802.3bt PDs that share the same detection features, hierarchical features, and maintained power features (MPS) between two pairs of pairs, While dual-feature PDs are 802.3bt PDs with independent features between the two pairs.Undoubtedly, the new 802.3bt designs will tend to favor simpler and more cost-effective single-feature topologies that only require Single PD Interface Dual Feature The PD requires two parallel PD interfaces (one for each pair), and the power from both PSEs is added after each PD interface For example, the dual feature topology essentially uses two 25.5W PD to form a single 51W PD, a complex solution that can cost as much as double the single-featured 51W PD.
The 802.3bt detection process has been extended to not only identify PDs that are connected as 802.3-compliant PDs, but also to determine whether a single-feature PD or a dual-feature PD is connected. Because of this, detection now uses 'connection checking' Connection Check has been expanded to determine the single or dual feature PD configuration.
The 802.3bt specification introduces four new classes of high-power PDs, bringing the total number of single-feature classes to nine, as shown in Table 1. Class 5-8 is new to the PoE standard and translates to 40.0 W to 71.0 W. The PSE still has the option of grading the PD using either the physical layer (ie, 5-Event Fraction for 71W) or the data link layer (ie, Link Layer Discovery Protocol, LLDP), and PD still has to be able to support two grading schemes to match the standards In addition, 802.3bt can also implement an optional extension to the physical layer hierarchy (called 'Autoclass') in which an 802.3bt PSE measures a PD For example, this convenient power management feature allows the PSE to allocate the remaining power to an additional light bulb (if it knows that a particular light bulb draws less than its grading power).
Table 1: IEEE 802.3bt PD classification and power levels
For those users who require PDs in Deep-sleep mode, they will be happy to find that the 802.3bt specification proposes a lower-power version of Maintain Power Features (MPS), known as 'Low MPS.' Depending on the older PoE Standard, the PD must sink a small DC current with a duty cycle of 32% to instruct the PSE to keep the PD in the on state, however, this relatively high duty cycle will quickly become one in some applications For example, when you consider a new 'energy efficient' building standard, 802.3bt PDs currently only need to maintain a small DC current with ~ 2% duty cycle, thus drastically reducing standby current.
The types and characteristics of 802.3bt PDs are summarized in Table 2. You may already be familiar with Type 1 and Type 2 PDs, which are proposed by the 802.3af and 802.3at specifications, respectively, and are typically mapped to one or more unique hierarchies (Power level). However, the new Type 3 and Type 4 PDs for 802.3bt are not that easy. As can be seen from the 'PD Rating' column, Type 3 PD covers and extends Type 1 and Type 2 PD Similarly, Class 5 is used by Type 3 single-feature and Type 4 bi-directional PD In addition, as can be seen from Figure 2, a Class 5 single-feature PD is only assigned 40W and a Class 5 Dual-featured PDs are then assigned 2 x 35.5W; in dual-featured PDs this can be worse because each pair works independently and each pair may be at a different grade, for example: the first one A double feature Class 1.2 (10.3W) PD is formed for Class 1 (3.84W) on top and Class 2 (6.49W) on the second pair. As all such classifications overlap and non-standard The surge in power levels is important to developers and users No longer equates the PD type to the PD classification, nor does it consider the PD classification synonymous with the PD power level.Alternatively, the PD's feature topography and classification are explicitly identified and the PD's 'type' truthfully examined The meaning will be the most beneficial for everyone.
Table 2: Summary of IEEE 802.3bt PD Types and Features
It goes without saying that 802.3bt is backward compatible with 802.3at and 802.3af. A lower power 802.3at or 802.3af PD can be connected to a higher power 802.3bt PSE without any problem. Also, when the situation is reversed Over time, a higher-power 802.3bt PD connects to a lower-power 802.3at or 802.3af PSE, and PDs need to be able to operate in their respective lower-power states, which is called degraded. If PD Ignoring the degradation and operating at its highest power state, a high-power PD will cause the PSE to repeatedly turn on, reach its current limit, and then shut down. This effectively causes the PSE to generate low-frequency parasitic oscillations. Thus, 'downgrade' is 802.3at and 802.3af specifications, it is regrettable that this has been overlooked in many implementations.
Use all available power whenever possible
The most important aspects of high-power PD designs are usually cost and efficiency, which are largely chosen for the ICs that implement the PD interface. In addition, developers engaged in space-constrained design are also painfully aware of how to limit The size of the PD will only be a bigger challenge as higher power levels require the use of larger discrete components and larger heat sinks, and Analog Devices offers three models designed to maximize 802.3bt PD performance , Perhaps more importantly, a specially designed IC that simplifies the task of the task Figure 2 shows a simplified block diagram of the high efficiency single-feature 802.3bt PD interface with one auxiliary input with more than 94% of the end-to-end (RJ-45 input to PD load) efficiency and -40 ° C to 125 ° C temperature range.
AUX INPUT: Auxiliary input DC TO 600Hz: DC to 600HzDATA PAIRS: Data line pair SPARE PAIRS: Spare line pair
IDEAL DIODE BRIDGE CONTROLLER: IDEAL DIODE BRIDGE CONTROLLER MAXIMIZES POWER EFFICIENCY: MAXIMIZING POWER EFFICIENCY RADEUCES HEAT, ELIMINATES THERMAL DESIGN PROBLEMS: Reducing Heat and Eliminating Thermal Design Issues DC TO 600Hz: DC to 600Hz 9V TO 72V OPERATING VOLTAGE RANGE: 9V to 72V OPERATING VOLTAGE RANGE IQ = 1.5mA (TYPICAL): IQ = 1.5mA (Typical) FORWARD OR FLYBACK DISCRETES: Forward or Flyback Discrete Circuit
PD FORWARD / FLYBACK CONTROLLER: PD Forward / Flyback Controller • IEEE 802.3bt COMPLIANT: IEEE 802.3bt Compatible • HIGH EFFICIENCY FORWARD OR NO-OPTO FLYBACK OPERATION: High Efficiency Forward or Optocoupler Flyback Operation • SUPERIOR SURGE PROTECTION (100V): Excellent Surge Protection (100V) • Wide Junction Temperature TEMPERATURE RANGE (-40 ° C TO 125 ° C): Wide Junction Temperature Range (-40 ° C to 125 ° C)
PoE DIODE BRIDGE CONTROLLER: PoE Diode Bridge Controller MAZIMIZED POWER EFFICEINCY: Maximizes Power Supply Efficiency REDUCINATES THERMAL DESIGN PROBLEMS: Reduces Heat and Eliminates Thermal Design Problems LESS THAN 800uA QUIESCENT OPERATING CURRENT: Less than 800uA Static Operation CURRENT FULLY COMPATIBLE WITH IEEE 802.3 DETECTION AND CLASSIFICATION: Fully Compatible with IEEE 802.3 Detection and Classification
The LT4321 shown on the RJ-45 connector in Figure 2 is an ideal diode-bridge controller that replaces two diode-bridge rectifiers (Figure 1). The LT4321 uses a low-power N-channel MOSFET bridge to simultaneously increase PD Available power and reduced heat dissipation The 802.3bt specification requires the PD to accept a DC supply voltage of any polarity at its Ethernet input so that the LT4321 can smooth the power supply from the data line pair and the free pair to their Integrated into a single power supply with the correct polarity Polarity Reduced overall circuit size and cost due to the fact that power efficiency is virtually eliminated by cooling requirements Reduced power by 10x or more allows the PD to stay within the classified power budget , Or to enable PD to add functionality.
Behind the ideal diode bridge controller in Figure 2 is the PD Hub's 'Brain Hub' LT4295, an 802.3bt-compliant PD interface controller that integrates a high-efficiency forward or no-opto-coupled flyback Controller The LT4295 supports all nine PD stages and all four PD types with an integrated 25kΩ characteristic resistor, up to 5 event staging and a single feature topology. In addition to providing more PD power, the LT4295 The factor in the traditional PD controller is that it uses an external power MOSFET to drastically reduce overall PD heat dissipation and maximize power efficiency, which again becomes even more important as the power level of 802.3bt is higher. This novel approach allows users to select the MOSFET size for the specific thermal and efficiency requirements of the application, allowing the use of MOSFETs with on-resistances as low as 30mΩ.
If 802.3bt's 71.0W gives you the desire for more power, look for the ADI LTPoE ++ PSE and PD controller families that provide power levels as high as 90 W. The LTPoE ++ specification uses a system similar to the 802.3bt specification LTPoE ++ PSE controllers reliably communicate with LTPoE ++ PD controllers while maintaining interoperability with 802.3at and 802.3af devices. With just one cable, LTPoE ++ PD can be implemented in LTPoE ++ PSE 'Plug and Play' and all handshakes are handled automatically by hardware without the need for software!
Finally, the LT4320, shown at the top of Figure 2, is a 9V to 72V Ideal Diode Bridge Control for those 802.3bt PDs that must support an auxiliary power supply (PDs can be powered by a single power adapter in addition to PoE) Device that replaces all four diodes in a full-wave bridge rectifier with a low-loss N-channel MOSFET to significantly reduce power dissipation and increase usable voltage.Because cumbersome and expensive heat sinks are eliminated due to improved power efficiency, Thus reducing the size of the power supply and wall transformers.In addition, additional margins are provided by virtually eliminating two full diode drops (~ 1.2V at 12V, 10% at 12V) inherent in thermally running diode bridges (thereby increasing The application of the reserve space), low-voltage applications can benefit from.
in conclusion
While the IEEE 802.3bt is still a long way from being finalized, as the major aspects of the standard begin to tumble, developers can now confidently develop products for this market. The 802.3bt specification for PD types, topologies, and grading Supports higher power levels (up to 71.0W), while the new MPS features support lower standby power while the PD is asleep.As a pioneer in PoE technology and as an active member of the IEEE task force, Analog Devices, with the release of 802.3bt And LTPoE ++ PD and PSE controllers continue to be at the forefront of PoE technology.Is to take advantage of these to simplify the design, maximize power efficiency, minimize size and reduce overall BOM cost of the IC, and first to become the 802.3bt market supply This is up to the smarter, knowledgeable developer like yours.