AND8333/D High Power PoE Applications 1.0 Scope This application note explains how the NCP1081 PoE-PD device can be used to deliver high power levels to applications over the Ethernet cable. Sufficient information is included to create complete end-to-end solutions with high power PoE-PSE equipment available on the market. An overview of different options and configurations is provided. 2.0 High Power Equipment 2.1 High Power PSE Equipment: Midspans and Power Injectors The IEEE802.3af standard supports up to 13W of power distributed over the Ethernet cable. The IEEE802.3at (Draft 3.0) standard supports power levels up to 25.5W. Both standards describe power distribution over two pairs from the four pairs of the Ethernet cable as shown in Figure 1. PSE PD Data UTP 48V Data Power Sourcing Equipment (PSE) Powered Device (PD) Data Power Sourcing: IEEE 802.3af Voutaf = 44 … 57 V Pminaf = 15.4 W IEEE 802.3at Voutat = 50 … 57 V Pminat = 30 W DC supply generation Data Line (100m): Rmaxcat5 = 20 Ohms Vdrop = 7 V Icable=350mA Rmaxcat6 = 12.5 Ohms Vdrop = 9 V Icable=600mA Powered Device: Voutaf = 37 … 57 V Pmaxaf = 12.95 W Voutat = 41 … 57 V Pmaxat = 25.5 W Figure 1: IEEE 802.3 Standard Power Distribution Over Two Pairs ©2008 SCILLC. All rights reserved. April 2008 – Rev. 2 Publication Order Number: AND8333/D AND8333 The higher power level for the IEEE802.3at standard is accomplished by raising the minimum IEEE803.3af standard voltage on the cable from 44V to 50V. CAT5e/6 cable is proposed for high power applications due to lower resistance. The power level in IEEE802.3at is increased from 13W to 25.5W by also changing the maximum cable current from 350mA to 720mA. Note that the 25.5W power budget is not fully available for the PD load due to losses which occur in the PD circuit between the Ethernet input jack and the voltage regulator output. Power losses occur in the DC-DC converter block, in the input diode bridge and also in the PoE-PD device. An overall efficiency of 85 percent is realistic. This results in an application power budget of 11W for IEEE802.3af and 20.4W for IEEE802.3at. Table 1: Power Budget Levels Cable (length 100m) Pairs used Cable resistance (Ohm) Max. current per pair (mA) Voltage by PSE (V) Power by PSE (W) Max. cable power loss (W) Input power PD (W) Efficiency of PD+ converter Output power PD (W) Overall efficiency IEEE 802.3af Cat 3 2 20 350 44 15.4 2.4 12.9 85% 11.0 71% IEEE 802.3at Cat 5e 2 12.5 600 50 30 4.5 25.5 85% 20.4 70% Option A Cat 5e 2 12.5 720 56 40.3 6.48 33.8 85% 28.7 71% Option B Cat 5e 2 12.5 1100 56 61.6 15.1 46.4 85% 39.5 64% Option C Cat 5e 4 12.5 550 56 61.6 7.5 54.0 85% 45.9 75% Option D Cat 5e 4 12.5 720 56 80.6 12.9 67.6 85% 57.5 71% Some PoE applications require more power than the 25.5W possible with the IEEE802.3at (Draft 3.0) standard which limits the current to 600mA. The mean reason for this limit is to reduce the generation of heat when a large number of Ethernet cables are bundled. Fortunately, it is possible to achieve higher power levels with proprietary configurations. Option A achieves higher power levels by increasing the minimum voltage level to 56V and the current up to 720mA. Option B combines raising the voltage to 56V and the current to 1100mA over two pairs. Option C delivers more output power than Option B but distributed over four pairs with a lower current 520mA per pair. Option D delivers about twice the power of Option A by distributing power over four pairs instead of two. Figure 2: PoE Injector Midspans are multiport power injectors placed in series with switches. An injector is a single port midspan. Figure 2 gives an overview on how a single port midspan (injector) injects power into the Ethernet cable. The power is retrieved from the cable via a splitter box. The NCP1081 can replace the high power splitter box delivering the required high power levels. Rev. 2 | Page 2 of 8 | www.onsemi.com AND8333 Table 2 lists high power PSE switches, midspans and injector equipment currently available on the market. Two- and four-pair configurations are available. • Phihong o o o o Phihong has midspans and injectors in their product line. Phihong has two-pair configurations up to 30W and 36W and four-pair versions up 60W and 80W. The four-pair configurations have proprietary detection and the two-pair configurations have Class 4 classification. Class 4 classification does not include a Layer 2 handshake since the midspan had no data communication channel. One NCP1081 device in combination with the Phihong two-pair 36W device can deliver 25W output power to the application with Class 4 classification (single-finger IEEE802.3at classification). Two NCP1081 devices in combination with the Phihong two-pair Option C and D approach can be implemented with four-pairs to deliver more than 40W to the application. • Korenix o Korenix has Ethernet switches with 30W per port. The equipment uses Class 4 and some include Layer 2 handshaking. The NCP1081 can only deliver 20W to the application in combination with this equipment. o o Panduit midspan delivers 30W per port. Classification is via Class 4 without Layer 2 handshaking. The NCP1081 can only deliver 20W to the application in combination with this equipment. o • Panduit Table 2: Overview of High Power PSE Equipment Company Type Name Power Watt Phihong Korenix Panduit Injector Injector Injector POE20U POE30U POE60U 19.6 30 60 PSE Power Power Output/Port 19.6 30 60 PD Power PD Output Ports Pairs Voltage Volt 14 20 40 1 1 1 2 2 4 56 56 56 Current mA/per Pair 350 550 550 Injector POE80U 80 80 57 1 4 56 720 Midspan POE480U-4UP 240 60 40 4 4 ? ? Midspan POE480U-8UP 480 60 40 8 4 ? ? Midspan Midspan Switch Switch Midspan POE576U-8HP POE576U-16HP Jetnet 4706 Jetnet 3706 DPOE8 288 576 120 120 240 36 36 30 30 30 25 25 20 20 20 8 16 4 4 8 2 2 2 2 2 ? ? 55 55 ? 550 550 650 650 ? Handshake Class 4 Class 4 Proprietary 12.5K detection Proprietary 12.5K detection Proprietary 12.5K detection Proprietary 12.5K detection Class 4 Class 4 Class 4 Layer 2 Class 4 Layer 2 Class 4 2.2 Handshaking Protocols The NCP1081 can handle all defined types of handshaking and is compatible with all the PSE equipment described above. The classification process defined in the high power IEEE802.3at standard extends beyond the one defined in the low power 802.3af standard because it can be done in several ways. First the classification current in the PoE-PD must be set to the Class 4. Then the PoE-PD can be classified by the IEEE802.3at PSE based on Two Event Physical Layer classification (so called Layer 1), Data Link Layer classification (so called Layer 2) or a combination of both. However, high power PSE which are non compliant with the previous process can also be used with the NCP1081 if they use a proprietary current classification. These handshaking protocols are explained in more detail in the following paragraphs. 2.2.1. High Power Classification: Two Event Physical Layer Classification (Layer 1) This first method is characterized by a classification event being performed twice, meaning the PSE forces the PD to enter in the classification range two times. This is implemented in the hardware of the PSE and PD devices. Interest in this Layer 1 approach is mainly driven by the need for basic midspan equipment where it is desirable to avoid having to access the data channel stream. None of the equipment above is using this classification principle but the standard is evolving in this way for midspans and injectors. Rev. 2 | Page 3 of 8 | www.onsemi.com AND8333 2.2.2. High Power Classification: Layer 2 Classification A PSE performing Layer 2 classification classifies the PD in two phases. In the first phase the PSE performs a physical classification with one event (same procedure used in the IEEE802.3af standard). The classified PD is then powered up by the PSE under low power conditions, meaning that the power can not exceed the IEEE802.3af limits. The second phase occurs a very short period after powerup; the PD will communicate its required power level to the PSE via an Ethernet data packet. The IEEE802.3at draft specification suggests using the link layer discovery protocol (LLDP) according to the IEEE802.1AB-2005 specification that is being reworked and follows the messages described in the IEEE802.3at specification. The designer will have to implement a LLDP agent, a software routine implementing a state machine that is providing access to the internal data base of the network device. Not all of the databases, such as management information base (MIB) that are commonly accessible via LLDP need to be implemented, but for sure the IEEE802.3at power management data sets needs to be implemented. 2.2.3. High Power Classification: Proprietary A third method is proprietary. Since most midspan equipment does not currently support Layer 1 handshaking, most of the PSE equipment today uses a proprietary classification, typically using a one event physical classification handshake. • Proprietary detection resistors are possible to enable four-pair configurations. The Phihong equipment uses a 12.5K Ohm resistor instead of 25K Ohm detection resistor. • Another option is to use a one event Layer 1 classification using Class 4 to enable higher power levels without doing a Layer 2 classification. Most of the equipment above is using this principle. This principle is actually a single-finger Layer 1 handshake with reserved Class 4. 2.2.4. Handshaking Indication The nCLASS_AT pin on the NCP1081 indicates to the microcontroller if a two event physical classification event occurred. Once it has been detected, the nCLASS_AT open drain pin goes low. In all other conditions, such as a one event physical classification handshake, the nCLASS_AT pin stays high. Powered Device Application Csup VSUP VDDL VDDL Layer 2 Engine Rbip Rled 20 uA nCLASS_AT IN1 Microprocessor or Microcontroller IN2 Opto1 Class_AT ARTN Features GND NCP1081 Isolation (Isolated DC/DC converter) Figure 3: nCLASS_AT Pin • Connecting the NCP1081 to a Phihong midspan keeps the nClass_AT pin high. • Connecting to an IEEE802.3at compliant midspan will bring the nClass_AT pin low. Rev. 2 | Page 4 of 8 | www.onsemi.com AND8333 3.0 High Power Configurations 3.1 20W or 30W Single Output Cpd VPORTP RJ-45 Rclass CLASS VDDH D1 T1 Voutput Cvddh Rinrush INRUSH VDDL Cline DB1 Z_line Data Pairs NCP1081 R1 Rd1 nCLASS_AT UVLO R2 M1 GATE TEST2 CS OSC SS VPORTN2 COMP VPORTN1 R5 Rslope FB TEST1 DB2 LD1 Cload ILIM1 Spare Pairs Cvddl Rilim1 ARTN OC1 Rcs R3 C2 RTN Optocoupler C1 Rosc Css Z1 R4 Figure 4: 30W, Two-Pair, Single Output Configuration • The POE30U midspan can deliver 30W of power to the cable by injecting 550mA at 56V. A single NCP1081 delivers 20W to a 24V output. The PoE-PD efficiency from input RJ45 jack to output is estimated to be 85 percent. Using a Cat5e 100m cable results in an overall efficiency from PSE output to PD converter output of 75 percent. • The POE480U-4P can deliver 36W of power to the cable by injecting 720mA at 56V. A single NCP1081 delivers 25W to a 24V output. The PoE-PD efficiency from input RJ45 jack to output is estimated on 85 percent. Using a Cat5e 100m cable results in an overall efficiency from PSE output to PD converter output of 71 percent. • The power can be increased to higher power levels by increasing the voltage or current limit. • Connecting the NCP1081 to a Phihong midspan keeps the nClass_AT pin high. Rev. 2 | Page 5 of 8 | www.onsemi.com AND8333 3.2 60W or 80W Triple Output Figure 5: 80W, Four-Pair, Triple Output Configuration • The POE60U midspan can deliver 60W of power to the cable by injecting 550mA at 56V. Dual NCP1081’s deliver 25W to a 24V output, 20W to a 12V output and 5W to a 3.3V output. The PoE-PD efficiency from input RJ45 jack to output is estimated to be 85 percent. Using a Cat5e 100m cable results in an overall efficiency from PSE output to PD converter output of 75 percent. • The POE80U midspan can deliver 80W of power to the cable by injecting 720mA at 56V. Dual NCP1081’s deliver 34W to a 24V output, 30W to a 12V output and 4W to a 3.3V output. The PoE-PD efficiency from input RJ45 jack to output is estimated to be 85 percent. Using a Cat5e 100m cable results in an overall efficiency from PSE output to PD converter output of 71 percent. • Connecting the NCP1081 to a Phihong midspan keeps the pin nClass_AT high. Rev. 2 | Page 6 of 8 | www.onsemi.com AND8333 3.3 60W or 80W Dual Output Figure 6: 80W, Four-Pair, Dual Output Configuration • The POE60U midspan can deliver 60W of power to the cable by injecting 550mA at 56V. Dual NCP1081’s deliver 25W to a 24V output and 25W to a 12V output. The PoE-PD efficiency from input RJ45 jack to output is estimated to be 85 percent. Using a Cat5e 100m cable results in an overall efficiency from PSE output to PD converter output of 75 percent. Other voltages can be derived from the 12V output with a separate DC-DC converter. • The POE80U midspan can deliver 80W of power to the cable by injecting 720mA at 56V. Dual NCP1081’s deliver 34W to a 24V output and 34W to a 12V output. The PoE-PD efficiency from input RJ45 jack to output is estimated to be 85 percent. Using a Cat5e 100m cable results in an overall efficiency from PSE output to PD converter output of 71 percent. Other voltages can be derived from the 12V output with a separate DC-DC converter. • Connecting the NCP1081 to a Phihong midspan keeps the pin nClass_AT high. Rev. 2 | Page 7 of 8 | www.onsemi.com AND8333 4.0 Company or Product Inquiries For more information about ON Semiconductor’s Power over Ethernet products visit our Web site at http://www.onsemi.com 5.0 Revision History Date January 2008 April 2008 Version 1.0 2.0 Modifications Initial release General update ON Semiconductor and are registered trademarks of Semiconductor Components Industries, LLC (SCILLC). SCILLC reserves the right to make changes without further notice to any products herein. SCILLC makes no warranty, representation or guarantee regarding the suitability of its products for any particular purpose, nor does SCILLC assume any liability arising out of the application or use of any product or circuit, and specifically disclaims any and all liability, including without limitation special, consequential or incidental damages. “Typical” parameters which may be provided in SCILLC data sheets and/or specifications can and do vary in different applications and actual performance may vary over time. All operating parameters, including “Typicals” must be validated for each customer application by customer's technical experts. SCILLC does not convey any license under its patent rights nor the rights of others. SCILLC products are not designed, intended, or authorized for use as components in systems intended for surgical implant into the body, or other applications intended to support or sustain life, or for any other application in which the failure of the SCILLC product could create a situation where personal injury or death may occur. Should Buyer purchase or use SCILLC products for any such unintended or unauthorized application, Buyer shall indemnify and hold SCILLC and its officers, employees, subsidiaries, affiliates, and distributors harmless against all claims, costs, damages, and expenses, and reasonable attorney fees arising out of, directly or indirectly, any claim of personal injury or death associated with such unintended or unauthorized use, even if such claim alleges that SCILLC was negligent regarding the design or manufacture of the part. SCILLC is an Equal Opportunity/Affirmative Action Employer. This literature is subject to all applicable copyright laws and is not for resale in any manner. PUBLICATION ORDERING INFORMATION LITERATURE FULFILLMENT: Literature Distribution Center for ON Semiconductor P.O. Box 5163, Denver, Colorado 80217 USA Phone: 303-675-2175 or 800-344-3860 Toll Free USA/Canada Fax: 303-675-2176 or 800-344-3867 Toll Free USA/Canada Email: [email protected] N. American Technical Support: 800-282-9855 Toll Free USA/Canada Europe, Middle East and Africa Technical Support: Phone: 421 33 790 2910 Japan Customer Focus Center Phone: 81-3-5773-3850 Rev. 2 | Page 8 of 8 | www.onsemi.com ON Semiconductor Website: www.onsemi.com Order Literature: http://www.onsemi.com/orderlit For additional information, please contact your local Sales Representative