Lightning Surge Protection for Power over Ethernet (PoE) Applications Using TCS™ High-Speed Protectors (HSPs) APPLICATION NOTE INTRODUCTION PT61020EL TCS-DL004-250-WH As an extension of the “Lightning Protection for Gigabit Ethernet (GbE) Applications Note [1]”, we will now review a very robust lightning protection circuit for Power over Ethernet (PoE) applications. The protection circuit is capable of withstanding severe lightning surges such as 4 kV 10/700 μs voltage surges per ITU-T K.44. The TCS™ High-Speed Protector (HSP) solution is expanded to include AC power-cross protection. CIRCUIT TO BE EVALUATED The TCS™ HSP circuit that will be evaluated is shown here in figure 1. A comparison between a conventional TVS diode based solution and the superior TCS™ HSP solution can be found in the “Lightning Protection for Gigabit Ethernet (GbE) Application Note [1]”. CDSOD323-T05C TCS-DL004 -250-WH CDSOD323-T05C MCT1 CDSOD323-T05C TCS-DL004 -250-WH SMLJ58A Gigabit Ethernet Transceiver MCT2 CDSOD323-T05C TCS-DL004 -250-WH MOV-07D820K MCT3 CDSOD323-T05C TCS-DL004 -250-WH MF-RM055/240 RJ45 Quad Transformer PT61020EL MCT4 MCT1 DC Supply SMLJ58A MOV-10D820K MCT2 Varies with PSE/PD Chipset Isolated DC/DC Converter MOV-10D820K MCT3 5/13 • e/K1322 Figure 1. MCT4 TCS™ HSP and Bidirectional TVS Diode Protection Circuit Lightning Surge Protection for Power over Ethernet (PoE) Applications Using TCS™ High-Speed Protectors (HSPs) CHARACTERIZATION OF DEVICES Before we evaluate the performance of this PoE protection solution, it would be beneficial to characterize each component of the solution and understand how it performs under surge conditions. PT61020EL ETHERNET TRANSFORMERS CDSOD323-T05C Figure 2 below illustrates such an effect of two Bourns® PoE transformers (SM51589L and PT61020L). Each Ethernet transformer was surged with a 100 A, 8/20 μs combination wave (per Telcordia® GR-1089-CORE Issue 6), the worst case maximum secondary surge current was measured with the secondary winding shorted. Notice the reduced secondary peak current, and also the shorter surge current duration. Primary Current (A) SMLJ58A MOV-07D820K 120 100 80 60 40 20 0 -20 0 1 2 3 Primary Current 4 5 6 Time (µs) 7 SM51589L 8 9 10 30 25 20 15 10 5 0 -5 Secondary Currents (A) TCS-DL004-250-WH Ethernet transformers may be designed and used as Lighting Isolation Transformers (LITs), which mitigate limited duration overvoltage and overcurrent. PT61020EL MF-RM055/240 Figure 2. 5/13 • e/K1322 Primary and Secondary Currents of Ethernet Transformers with Secondary Winding Shorted 2 Lightning Surge Protection for Power over Ethernet (PoE) Applications Using TCS™ High-Speed Protectors (HSPs) ETHERNET TRANSFORMERS (Continued) PT61020EL TCS-DL004-250-WH Figure 3 below further illustrates the surge mitigating capabilities of the Bourns® Model PT61020EL transformer. This PoE transformer was surged with a 100 A, 8/20 μs combination wave (per Telcordia GR-1089-CORE Issue 6), a 1.5 kV, 10/700 μs voltage surge (per ITU-T K.44) and a 4 kV, 10/700 μs voltage surge (per ITU-T K.44). The worst-case, maximum secondary surge currents were measured with the secondary winding shorted. Notice the reduced secondary peak currents and also the shorter surge current durations. In the TCS™ HSP solution proposed in figure 1, the PT61020EL transformer isolates longitudinal surges and mitigates transverse surges, reducing the requirements on the secondary-side solution that are needed to protect the Ethernet transceiver. CDSOD323-T05C MOV-07D820K Secondary Currents (A) SMLJ58A 45 40 35 30 25 20 15 10 5 0 -5 -1 0 1 2 1.2/50 12 ohms 1/2 kV 3 Time (µs) 4 10/700 4 kV 5 6 7 10/700 1.5 kV MF-RM055/240 Figure 3. 5/13 • e/K1322 Secondary Surge Currents of PT61020EL Transformer with Secondary Winding Shorted 3 Lightning Surge Protection for Power over Ethernet (PoE) Applications Using TCS™ High-Speed Protectors (HSPs) TCS™ High-Speed Protectors PT61020EL The new family of TCS™ HSP devices is comprised of low resistance, fast response current limiters that provide excellent protection for low-voltage communication circuits. See Reference [1] for additional information. Normalized Current (A) TCS-DL004-250-WH CDSOD323-T05C SMLJ58A 1.2 1.0 0.8 0.6 0.4 0.2 0 -0.2 -0.4 -0.6 -0.8 -1.0 -1.2 -40 -30 -20 -10 0 10 20 30 40 Voltage (V) Figure 4. MOV-07D820K MF-RM055/240 TCS™ HSP V-I Characteristic Figure 4 above illustrates the TCS™ HSP V-I curve. Notice that the TCS™ HSP has a foldback characteristic; the current folds back after the device is triggered and then slowly increases as the voltage across the device rises. This is analogous to how the clamp voltage of a TVS diode increases as the current through the device increases. Similarly, the TCS™ HSP is limited by its peak impulse voltage withstand Vimp, which would be the duality of a TVS diode peak pulse current IPP. In the solution proposed in figure 1, the Ethernet transceiver is well protected by the current limiting characteristic of the TCS™ HSP, regardless of the severity of lightning surge. The TCS™ HSP will limit the current into or out of the transceiver while the TVS diode shunts the remainder of the transformer’s secondary current. 5/13 • e/K1322 4 Lightning Surge Protection for Power over Ethernet (PoE) Applications Using TCS™ High-Speed Protectors (HSPs) Clamping Diodes PT61020EL The Bourns® Model CDSOD323-T05C and CDSOT23-S2004, along with a generic Model BAV99 diode were characterized in the “Lightning Protection for Gigabit Ethernet (GbE) Application Note”. Reproduced below in figure 5, the clamping voltage Vclamp is plotted against the transformer’s secondary surge current IP through each diode, when a 100 A, 8/20 μs combination wave is applied on the primary winding of the transformer. It is clear that the TVS diode CDSOD323-T05C has the lowest dynamic resistance. TCS-DL004-250-WH 25 20 Voltage (V) CDSOD323-T05C SMLJ58A 15 10 5 0 0 5 CDSOD323-T05C MOV-07D820K Figure 5. 15 10 Current (A) 20 CDSOT23-S2004 25 BAV99 Clamping Voltage vs. Surge Current for the Three Diodes Tested In the TCS™ HSP solution proposed in figure 1, TVS diodes are used to ensure that the voltage on the lines during surge do not exceed the peak impulse voltage withstand Vimp of the TCS™ HSP. MF-RM055/240 5/13 • e/K1322 5 Lightning Surge Protection for Power over Ethernet (PoE) Applications Using TCS™ High-Speed Protectors (HSPs) Metal Oxide Varistors (MOVs) – PoE Power Lines PT61020EL Bourns® Model MOV-07D820K Metal Oxide Varistor (MOV) was chosen to clamp the voltage on the PoE power lines, so as not to interrupt the operation of PSE/PD during surge events. A shunting type protector is suitable only when power-cycling is expected and acceptable. Shown in figure 6, the MOV-07D820K MOV has a typical Vclamp around 150 V during a 4 kV, 10/700 μs voltage surge. TCS-DL004-250-WH T CDSOD323-T05C Ch1 Max 148 V Ch2 Max 94.8 A SMLJ58A 1 MOV-07D820K 2 Ch1 MF-RM055/240 5/13 • e/K1322 Figure 6. 100 V Ch2 20.0 A M 200 µs A Ch2 11.6 A Clamping Voltage of MOV-07D820K 6 Lightning Surge Protection for Power over Ethernet (PoE) Applications Using TCS™ High-Speed Protectors (HSPs) TVS Diodes – PoE Power Line PT61020EL TCS-DL004-250-WH Where a lower clamping voltage on the input to the PoE DC/DC converter is desired, MOVs may be stacked in parallel to lower the effective dynamic resistance, hence clamping voltage. Alternatively, TVS diodes offer lower dynamic resistance than MOVs. TVS diodes can also be stacked in parallel to lower the effective dynamic resistance. TVS diode(s) may be used in parallel with MOV(s) as another method of improving clamping performance, such as when the TVS diode’s peak pulse current (IPP) is insufficient to meet the expected surge currents. It is recommended that coordinated impedance be placed between the TVS diode(s) and the MOV(s). CDSOD323-T05C T T Ch1 Max 44.0 A Ch1 Max 95.0 V Surge Current Through TVS Diode SMLJ58A Ch2 Max 95.0 A TVS Clamping Voltage at DC/DC Input 1 Surge Current Through MOV & TVS Diode Ch2 Max 44.4 A Surge Current Through TVS Diode 1 2 2 Ch1 50.0 A Ch2 50.0 A M 200 µs A Ch2 25.0 A Ch1 50.0 V Ch2 20.0 A M 400 µs A Ch2 6.00 A MOV-07D820K Figure 7. MF-RM055/240 5/13 • e/K1322 Clamping Voltage of SMLJ58A & MOV-07D820K on PoE Power Lines In the TCS™ HSP solution proposed in figure 1, the Bourns® Model SMLJ58A TVS diode is used in parallel with the Bourns® Model MOV-07D820K MOV to ensure that the clamping voltage on the PoE power lines is within 100 V as illustrated in figure 7, during a 4 kV, 10/700 μs voltage surge. 7 Lightning Surge Protection for Power over Ethernet (PoE) Applications Using TCS™ High-Speed Protectors (HSPs) Multifuse® PPTC Resettable Fuses PT61020EL TCS-DL004-250-WH Where an AC power fault is expected, resettable fuses are preferred for a low cost Criteria A-compliant solution (per ITU-T K.44). The Bourns® Model MF-RM055/240 PPTC resettable fuse was chosen to allow for Class 3 implementation (per IEEE 802.3afTM), taking into consideration a maximum ambient temperature of 85 ˚C typically required of industrial applications. This would naturally conform to the maximum 400 mA current limit specified as well. Where a Powered Device (PD) implementation of lower power classification is required, Bourns® Multifuse® PPTC Resettable Fuses offer a lower current trip limit (Itrip), making them an ideal solution without impacting the AC power fault protection. Figure 8 illustrates the various models available and corresponding trip currents at 23 ˚C. CDSOD323-T05C SMLJ58A Time to Trip (Seconds) 100 A B C D F G H E A = MF-RM005/240 B = MF-RM008/240 C = MF-RM012/240 D = MF-RM016/240 E = MF-RM025/240 F = MF-RM033/240 G = MF-RM040/240 H = MF-RM055/240 10 1 MOV-07D820K 0.1 0.1 1 10 Fault Current (Amps) Figure 8. Multifuse® PPTC Resettable Fuses for PoE Applications MF-RM055/240 5/13 • e/K1322 8 Lightning Surge Protection for Power over Ethernet (PoE) Applications Using TCS™ High-Speed Protectors (HSPs) Summary of Component Evaluation PT61020EL TCS-DL004-250-WH CDSOD323-T05C While the TCS™ HSP protects the Ethernet transceiver by ensuring that surge currents to the Ethernet transceiver will be limited, the proper selection of the PoE transformer and clamping diodes ensures the overall performance and integrity of the complete TCS™ HSP solution. A MOV, a TVS diode, or a combination of both devices clamps the PoE power line voltage during surges to prevent damage to the PoE isolated DC/DC converter. Where AC power fault protection is required, Multifuse® PPTC Resettable Fuses are chosen for the applicable power classification and placed on each powered line. Where less harsh surges are expected, the TCS™ HSP solution may be varied by choosing less robust PoE transformers and clamping diodes/TVS diodes/MOVs of higher dynamic resistances. Surge and AC Power Fault Tests SMLJ58A MOV-07D820K A summary of the tests performed on the TCS™ HSP solution proposed in figure 1 is shown below in table 1. The protection afforded by the TCS™ HSP solution is quite dramatic; it reduced the energy into the PHY to a couple of microjoules (~90 % improvement over conventional solutions), regardless of surge or AC power fault applied within rated limits. The effectiveness of the TCS™ HSP solution proposed in figure 1 enables designers to consider the variation in robustness of Ethernet transceivers. Table 1. MF-RM055/240 5/13 • e/K1322 Clamping Voltage of SMLJ58A & MOV-07D820K on PoE Power Lines Test Description Typical Differential Input Voltage at PHY Typical Current into PHY Approximate Energy into PHY 1.5 kV, 10/700 μs voltage surge per ITU-T K.44 A.6.1-1 (a and b) <6V < 300 mA 3 μJ 4 kV, 10/700 μs voltage surge per ITU-T K.44 A.6.1-1 (a and b) <6V < 300 mA 4 μJ 240 Vac, 60 Hz, 15 min. R = 10, 20, 40, 80, 160 Ω per ITU-T K.44 A.6.1-1 (a and b) <6V <300 mA (Worst-Case Maximum) — 9 Lightning Surge Protection for Power over Ethernet (PoE) Applications Using TCS™ High-Speed Protectors (HSPs) Lightning Surge – 1.5 kV, 10/700 μs Voltage Surge PT61020EL TCS-DL004-250-WH Figure 9 below illustrates the robustness of the TCS™ HSP solution proposed in figure 1. Despite the 37.5 A primary winding surge current in the Ethernet transformer applied by the 1.5 kV, 10/700 μs voltage surge, causing up to 20 A of secondary winding surge current (as shown in figure 3), the TCS™ HSP immediately limits this to ~250 mA entering the Ethernet transceiver. In other words, the TCS™ HSP solution would work to prevent surge currents from damaging the Ethernet transceiver under the tested conditions. T CDSOD323-T05C PHY + PHY - 2 Ch1 Max 5.64 V SMLJ58A Diff. PHY M Ch2 Min -2.04 A PHY Input Current Total Surge Current Ch3 Max 42.5 A MOV-07D820K Ch4 Max 490 mA 4 MF-RM055/240 Ch2 5.00 V M 400 ns A Ch4 Ch1 5.00 V Ch3 25.0 AΩ Ch4 200 mAΩ Math 5.00 V 400 ns T 20.00 % Figure 9. 5/13 • e/K1322 124 mA TCS™ Solution - 1.5 kV, 10/700 μs Voltage Surge 10 Lightning Surge Protection for Power over Ethernet (PoE) Applications Using TCS™ High-Speed Protectors (HSPs) Lightning Surge – 4 kV, 10/700 μs Voltage Surge PT61020EL Figure 10 below illustrates the robustness of the TCS™ HSP solution proposed in figure 1. Despite the higher 100 A primary winding surge current in the Ethernet transformer applied by the 4 kV, 10/700 μs voltage surge, the TCS™ HSP again immediately limits this to ~250 mA entering the Ethernet transceiver. The TCS™ HSP solution holds the stress on the PHY relatively constant even if higher surge levels are applied. TCS-DL004-250-WH T PHY + CDSOD323-T05C PHY - 2 Ch1 Max 6.80 V Diff. PHY SMLJ58A M Ch2 Min -3.10 V Total Surge Current PHY Input Current MOV-07D820K Ch4 Max 520 mA 4 Ch2 5.00 V M 400 ns A Ch4 Ch1 5.00 V Ch3 25.0 AΩ Ch4 200 mAΩ Math 5.00 V 400 ns T 20.00 % MF-RM055/240 5/13 • e/K1322 Ch3 Max 109 A Figure 10. 124 mA TCS™ HSP Solution - 4 kV, 10/700 μs Voltage Surge 11 Lightning Surge Protection for Power over Ethernet (PoE) Applications Using TCS™ High-Speed Protectors (HSPs) AC Power Fault – 230 Vac 60 Hz, 15 Min. PT61020EL TCS-DL004-250-WH CDSOD323-T05C SMLJ58A MOV-07D820K MF-RM055/240 5/13 • e/K1322 Table 2 summarizes the performance of the added Bourns® Multifuse® PPTC MF-RM055/240 under various AC power fault conditions. Larger fault currents trip the Multifuse® PPTC resettable fuses faster, tending to reduce the stress on the primary windings of the Ethernet transformer. The Ethernet transformer PT61020EL in the TCS™ HSP solution proposed in figure 1 has been chosen to withstand the worst-case scenario occurring between 0.55 A and 1.25 A (Ihold and Itrip of MF-RM055/240, respectively) where the typical time to trip is expected to exceed 30 seconds or possibly the entire 15 minute test. Table 2. Summary of AC Power Fault Test Results Test Description 240 Vac, 60 Hz, 15 Min. per ITU-T K.44 A.6.1-1 (a and b) Typical Fault Current Typical Time to Trip Approximate Transformer Power Dissipation R = 10 Ω 24 Aac ~ 80 ms 41.47 J R = 20 Ω 12 Aac ~ 160 ms 20.73 J R = 40 Ω 6 Aac ~ 800 ms 25.92 J R = 80 Ω 3 Aac ~3s 24.3 J R = 160 Ω 1.5 Aac ~ 30 s 60.75 J R = 300 Ω 0.8 Aac ~ 120 s 69.12 J R = 600 Ω 0.4 Aac — 129.6 J R = 1000 Ω 0.24 Aac — 46.65 J For example, when R = 600 Ω, the corresponding fault current of 0.4 Aac is below the maximum operating current of a Class 3 implementation (per IEEE 802.3af). By design, the MF-RM055/240 used in the TCS™ HSP solution proposed in figure 1 will not trip. Hence, the primary windings of the transformer must be rated to handle this level of current, making the PT61020EL transformer a good choice. 12 Lightning Surge Protection for Power over Ethernet (PoE) Applications Using TCS™ High-Speed Protectors (HSPs) AC Power Fault – 230 Vac 60 Hz, 15 Min. (Continued) PT61020EL Due to the low frequency nature of an AC power fault, an insignificant secondary fault current is induced. As long as the primary windings of the Ethernet transformer can withstand the fault currents prior to the Multifuse® PPTC resettable fuse tripping, the TCS™ HSP solution proposed in figure 1 will offer robust protection against an AC power fault as shown in figures 11 and 12 below. T TCS-DL004-250-WH T Primary Winding Fault Current Ch1 Max 252 mA 2 Ch2 Max 28.4 A CDSOD323-T05C 1 Ch1 Max 1.00 A Primary Winding Fault Current 2 Ch2 Max 4.83 A 1 Secondary Fault Current into PHY SMLJ58A Secondary Fault Current into PHY Ch1 200 mA Ch2 Figure 11. TCS™ HSP Solution – 240 Vac AC Power Fault, R = 10 Ω MOV-07D820K 20.0 A T M 10.0 ms A Ch2 7.60 A Ch1 500 mA Ch2 20.0 A M 1.00 µs A Ch2 330 mA Primary Winding Fault Current 1 MF-RM055/240 2 Secondary Fault Current into PHY Ch1 2.00 A 5/13 • e/K1322 Figure 12. Ch2 100 mA M 4.00 ms A Ch2 TCS™ HSP Solution – 240 Vac AC Power Fault, R = 160 Ω 560 mA 13 Lightning Surge Protection for Power over Ethernet (PoE) Applications Using TCS™ High-Speed Protectors (HSPs) 820.3-2008 Template and Amplitude Tests PT61020EL Complete IEEE 802.3 signal template and amplitude tests were conducted on the TCS™ HSP solution proposed in figure 1. Table 3 summarizes some of the test results. It can be seen that the addition of a TCS™ HSP had minimal impact on the quality of the test signal. Table 3. Summary of 802.3 Test Results TCS-DL004-250-WH CDSOD323-T05C SMLJ58A MOV-07D820K MF-RM055/240 5/13 • e/K1322 Test Specification Range Baseline Measured Value Bourns® TCS™ HSP Solution w/o Multifuse® PPTC Measured Value Bourns® TCS™ HSP Solution with Multifuse® PPTC Measured Value Template Test Point A Fit the Template Pass Pass Pass Template Test Point B Fit the Template Pass Pass Pass Template Test Point C Fit the Template Pass Pass Pass Template Test Point D Fit the Template Pass Pass Pass Template Test Point F Fit the Template Pass Pass Pass Template Test Point H Fit the Template Pass Pass Pass Peak Voltage Point A 670 mV to 820 mV 696.9 mV 690.0 mV (-6.9 mV / -0.09 dB) 678.3 mV (-18.6 mV / -0.24 dB) Peak Voltage Point B 670 mV to 820 mV 696.9 mV 690.4 mV (-5.6 mV / -0.07 dB) 677.9 mV (-18.1 mV / -0.23 dB) % Diff A and B <1% 0.14 % 0.07 % Point B Peak Voltage % Diff C <2% 0.81 % 0.61 % Point B Peak Voltage % Diff D <2% 0.11 % 0.09 % Point B 14 Lightning Surge Protection for Power over Ethernet (PoE) Applications Using TCS™ High-Speed Protectors (HSPs) 820.3-2008 Template and Amplitude Tests (Continued) PT61020EL The TCS™ HSP solution offers superior protection while not compromising signal integrity in any significant way. Even the addition of Multifuse® PPTC resettable fuses on the line-side of the Ethernet transformer does not impact signal integrity in any significant way. Figures 13 through 15 illustrate this. R1 200 mV 5.0 ns TCS-DL004-250-WH 6.0 ns/div -9.66 ns 20.0 GS/s IT 10.0 ps/pt C4 500 mV CDSOD323-T05C SMLJ58A Figure 13. Baseline Template Measurement (No Protection Devices) IEEE Std 802.3ab, Sec 40.6.1.2.3: 1000Base-T Differential Output Template Point A R1 200 mV 5.0 ns 5.0 ns/div -9.06 ns 20.0 GS/s IT 10.0 ps/pt C4 499 mV MOV-07D820K MF-RM055/240 Figure 14. Template Measurement (TCS-DL004-250-WH) IEEE Std 802.3ab, Sec 40.6.1.2.3: 1000Base-T Differential Output Template Point A R1 200 mV 5.0 ns 5.0 ns/div -8.81 ns 20.0 GS/s IT 10.0 ps/pt C4 500 mV Figure 15. 5/13 • e/K1322 Template Measurement (TCS-DL004-250-WH and MF-RM055/240) IEEE Std 802.3ab, Sec 40.6.1.2.3: 1000Base-T Differential Output Template Point A 15 Lightning Surge Protection for Power over Ethernet (PoE) Applications Using TCS™ High-Speed Protectors (HSPs) Summary Figure 1 shows a very robust lightning protection circuit for PoE applications, capable of severe lightning surges within rated limits, such as 4 kV 10/700 μs voltage surges (per ITU-T K.44). Each component of the solution was reviewed and the surge and AC power fault capability of the solution was shown. In addition, the minimal impact on signal integrity was demonstrated. PT61020EL The TCS™ High-Speed Protector provides excellent protection and is well-suited for lowvoltage, high-speed communication circuits. TCS-DL004-250-WH CDSOD323-T05C SMLJ58A REFERENCE [1] A. Morrish and L. Stencel, (2012 Oct 16). Robust Protection and Excellent Signal Quality for Gigabit Ethernet Applications Using Transient Current Suppressor (TCS™) Technology White Paper [Online]. Available at: MOV-07D820K http://www.bourns.com/data/global/pdfs/Bourns_TCS_GBE_White_Paper.pdf MF-RM055/240 ADDITIONAL RESOURCES For more information visit Bourns online at: www.bourns.com COPYRIGHT© 2013 • BOURNS, INC. • 5/13 • e/K1322 “TCS” is a trademark of Bourns, Inc. in the U.S. and other countries. “Bourns” and “Multifuse” are registered trademarks of Bourns, Inc. in the U.S. and other countries. Americas: Tel +1-951 781-5500 5/13 • e/K1322 Fax +1-951 781-5700 EMEA: Tel +41-(0)41 768 55 55 Fax +41-(0)41 768 55 10 Asia-Pacific: Tel +886-2 256 241 17 Fax +886-2 256 241 16 16