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Lightning Surge Considerations for PoE Power Sourcing Equipment Devices

Application ReportSLUA818–February 2017

Lightning Surge Considerations for PoE Power SourcingEquipment Devices

Eric Wright, Penny Xu, Donald V. Comiskey

ABSTRACTThis report considers the implementation of lightning surge protection for Power over Ethernet (PoE)powered sourcing equipment (PSE) applications. The necessity for implementing such protection willnormally depend on the environment in which the PSE is intended to operate and the inherent isolationproperties of the PSE. There are numerous compliance standards to consider when establishing the surgeprotection level of the PSE. These standards normally introduce a number of test conditions for varioustypes of products ranging from main's power supplies to legacy telephone equipment. This reportexamines the various standards in an effort to relate the test conditions that would most likely beapplicable to PoE PSE applications and provides suggestions for meeting the associated surgerequirements.

This report is based on information that was available in May 2009. The most recent version of thereferenced standards should be consulted when applying the information provided in the report.

Contents1 Relating IEEE 802.3, IEC 60950, and ITU-T K.44 Standards ......................................................... 22 IEC 61000-4-5:2005 Standard ............................................................................................. 43 Determining the Peak Surge Current ..................................................................................... 54 PSE Surge Protection Application ......................................................................................... 95 Choosing the SPDs for High Voltage Surge PSE Applications ...................................................... 106 Reference Design .......................................................................................................... 137 Test Report.................................................................................................................. 188 Conclusion .................................................................................................................. 209 References .................................................................................................................. 20

List of Figures

1 ITU-T K.44 Impulse Generator as Defined in Figure N.1 of IEC 60950-1 Standard................................ 22 10/700-µs Surge Generator as Defined in Figure A.3-1 of ITU-T K.44 Standard ................................... 33 Expanded Eight-Wire PoE PSE Test Setup Based on Figure 14 of IEC 61000-4-5:2005 Standard. ............ 44 Example of Surge Current Paths Through Earthed-PSE Application................................................. 95 Using MOV Repetitive Surge Capability Curves ....................................................................... 126 Using the MOV Maximum Clamping Voltage Curves ................................................................. 127 PR2189E1 Reference Design Layout ................................................................................... 148 Schematic One ............................................................................................................. 159 Schematic Two ............................................................................................................. 1610 Schematic Three ........................................................................................................... 1711 Test Equipment............................................................................................................. 1912 Test Setup................................................................................................................... 19

List of Tables

1 Short-Circuit Current of 10/700-µs Impulse Generator Based on 40-Ω Effective Output Impedance ............ 32 PoE PSE Test Scenarios ................................................................................................... 5

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C120 µF

C20.2 µF

R150

R215

R325

SurgeOutput

UcChargingVoltage

SurgeEnable

Relating IEEE 802.3, IEC 60950, and ITU-T K.44 Standards www.ti.com

2 SLUA818–February 2017Submit Documentation Feedback



3 Configuration One: Surge Applied From Lines to Ground (or Earth) With Other Lines Open..................... 64 Configuration Two: Surge Applied From Lines to Ground (or Earth) With Other Lines Grounded ............... 75 Maximum Configuration One and Configuration Two Center-Tap Currents: 10/700 and 1.2/50 Waveforms ... 86 Maximum Configuration Two Center-Tap Currents: 10/700 and 1.2/50 Waveforms ............................... 87 Requirements for Four-Port Design Example ......................................................................... 10

TrademarksBourns is a trademark of Bourns, Inc..Littlefuse is a trademark of Littelfuse, Inc..UltraMOV is a registered trademark of Littlefuse, Inc..All other trademarks are the property of their respective owners.

1 Relating IEEE 802.3, IEC 60950, and ITU-T K.44 StandardsThe IEEE 802.3 standard, which defines the PoE system, specifies that the PSE will provide electricalisolation that withstands at least one of the following electrical strength tests:(a) 1500 Vrms at 50 Hz to 60 Hz for 60 sec is applied as specified in subclause 5.2.2 of IEC 60950-

1:2001.(b) 2250 Vdc for 60 sec is applied as specified in subclause 5.2.2 of IEC 60950-1:2001.(c) An impulse test consisting of a 1500-V, 10/700-µs waveform is applied ten times with a 60-sec interval

between pulses. The shape of the impulses must be 10/700 µs (10-µs virtual front time, 700-µs virtualtime to half value), as defined in IEC 60950-1:2001 Annex N.

The third electrical strength test in the previous list is seen to describe an impulse test in accordance withIEC 60950-1 Annex N. This annex of the IEC 60950-1 standard provides the following definition for theimpulse generator. The circuit and component values referred to in the definition are summarized inFigure 1.

N.1 ITU-T Impulse Test GeneratorsThe circuit in Figure N.1, using the component values in references 1 and 2 of Table N.1, is usedto generate impulses, the C1 capacitor being charged initially to a voltage Uc.Circuit reference 1 of Table N.1 generates 10/700 µs impulses (10 µs virtual front time, 700 µsvirtual time to half value) as specified in ITU-T Recommendation K.44 to simulate lightninginterference in the telecommunication network.

Figure 1. ITU-T K.44 Impulse Generator as Defined in Figure N.1 of IEC 60950-1 Standard

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C120 µF(Uc)

C20.2 µF

R150

R215

SurgeOutputs

SurgeEnable

Rg1

g2

gn-1

gn

Return

R

R

R

R = 25 [(number of lines)

www.ti.com Relating IEEE 802.3, IEC 60950, and ITU-T K.44 Standards




The 10-µs virtual front time and 700-µs virtual time to half value impulse shape refers to the open-circuitvoltage waveform of the impulse generator. The 15-Ω resistor (R2) and 25-Ω resistor (R3) shown inFigure 1 combine to provide an effective output impedance of 40 Ω. The peak short-circuit currentprovided by the impulse generator for various voltage levels based on this effective output impedance isoutlined in Table 1. The resulting short-circuit current waveform will have a 5-µs virtual front time and a320-µs virtual time to half value, so the generator is commonly referred to as a 10/700-µs to 5/320-µscombination wave generator (in accordance with IEC 60060-1).

Table 1. Short-Circuit Current of 10/700-µs Impulse Generator Based on 40-Ω Effective OutputImpedance

10/700-µs to 5/320-µs COMBINATION WAVE GENERATORPEAK OPEN-CIRCUIT VOLTAGE PEAK SHORT-CIRCUIT CURRENT

500 V 12.5 A1000 V 25 A1500 V 37.5 A2000 V 50 A4000 V 100 A

As stated above, the IEC 60950-1 standard defines an impulse generator to simulate lightning interferencein accordance with the ITU-T K.44 standard. Referring to Figure A.3-1 of the ITU-T K44 standard, the10/700-µs impulse (surge) generator is further defined to use multiple resistors in place of the single 25 Ωresistor (R3 in Figure 1) in order to divide the surge current into multiple conductors simultaneously, whilemaintaining an overall output impedance of 40 Ω. This is shown in Figure 2 and would imply the use ofeight resistors for PoE applications, where an eight-wire (four twisted-pairs) symmetrically balancedcabling system is used (that is, CAT-5 and CAT-6 cable).

Figure 2. 10/700-µs Surge Generator as Defined in Figure A.3-1 of ITU-T K.44 Standard

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RR R R R R R R

10/700 usCombination Wave

Generator

EUT(PoE PSE)

DecouplingNetwork

ProtectionEquipment

AuxiliaryEquipment(PoE PSE)

8-wireCAT-5 Cable

Earth Ground

1

2

3

6

4

5

7

8

(8) 200 ohm resistors

(8) coupling elements

Return

Coupling Network

Req = 25

Rint = 15

Output

IEC 61000-4-5:2005 Standard www.ti.com




2 IEC 61000-4-5:2005 StandardThe IEC 61000-4-5:2005 standard specifies two types of surge generators as follows:

Two types of combination wave generators are specified. Each has its own particular applications,depending on the type of port to be tested. The 10/700 µs combination wave generator is used totest ports intended for connection to symmetrical communication lines. The 1.2/50 µs combinationwave generator is used in all other cases, and in particular, for testing ports intended for powerlines and short-distance signal connections.

The 10/700-µs surge generator referred to in the IEC 61000-4-5:2005 standard is further described to bein accordance with that defined in the ITU-T K44 standard. Figure 14 of the IEC 61000-4-5:2005 standardincludes an example of the setup used for testing unshielded symmetrical lines which would be applicableto the type of cabling system used in a PoE system. Figure 3 expands on this test setup to show theconnections required for the eight-wire input associated with the PSE.

Figure 3. Expanded Eight-Wire PoE PSE Test Setup Based on Figure 14 of IEC 61000-4-5:2005 Standard.

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www.ti.com Determining the Peak Surge Current




As seen in Figure 3, eight 200-Ω resistors are used along with eight coupling elements, typically gasarrestors, to couple the surge from the generator output to each line of the eight-wire cablesimultaneously. The 200-Ω value of the resistors is compliant with the 250-Ω maximum defined in the IEC61000-4-5:2005 standard. The parallel combination of the eight 200 Ω resistors provides an equivalentresistance of 25 Ω which would be in series with the internal 15 Ω resistance associated with the surgegenerator. This total resistance satisfies the 40-Ω effective output impedance and peak short-circuitrequirements discussed in Section 2.

The IEC 61000-4-5:2005 standard also specifies a 1.2/50-µs generator for use in performing lightningsurge tests on power lines and short-distance signal applications. Some PSE applications may fall underthe short-distance category where the tests are performed using the 1.2/50-µs generator instead of the10/700-µs to 5/320-µs combination wave generator. The 1.2/50-µs generator is commonly referred to as a1.2/50-µs to 8/20-µs combination wave generator, because it is a short-circuit current waveform has an 8-µs virtual front time and a 20-µs virtual time to half value.

Another physical consideration of PoE is discussed on page seven of theElectrical Transient Immunity forPower-Over-Ethernet[2] application report:

On a twisted-pairs cable, the two wires of each pair are twisted together, but there is no twisting betweenpairs at all (in fact, each pair is well separated from its neighbors). Consequently, a differential-modetransient between P and N is likely with that type of cable, and this tandem of pairs can be considered asan unbalanced line as far as the test voltages are concerned.

The implication is that the unbalanced circuit and lines category is also applicable for PoE as is the 1.2/50-µs combination wave generator. Under these assumptions, Table 2 outlines several test scenarios usingboth an eight-wire and four-wire coupling-decoupling network (CDN).

Table 2. PoE PSE Test Scenarios

TEST CONDITION EIGHT-LINE CDN FOUR-LINE CDNCommon mode (line-earth) 8-wires to earth 4-wires to earth

Single wire differential 1-wire shorted to earth with surge appliedto 7-wires

1-wire shorted to earth with surge appliedto 3-wires

Single pair differential 1-PoE pair shorted to earth with surgeapplied to other 3-pairs

1-PoE pair shorted to earth with surgeapplied to other pair

3 Determining the Peak Surge CurrentThe peak current per line needs to be considered when selecting the surge current rating of componentswithin the PSE, including any surge protection devices (SPDs). The path of the surge must be understoodto determine whether the component will see the current associated with one line or an additive currentassociated with multiple lines. Additionally, there could be other worst case scenarios such as when onlyone line or one twisted pair is subjected to the surge with the other lines open. It should be noted, that thesurge test is not normally performed with some of the lines open; rather the differential surges will beapplied as described in Table 2. Other examples include extending the surge voltage to levels above 4kVand testing only four lines instead of eight.

Table 3 and Table 4 show the per-wire currents for both the 10/700-µs and 1.2/50-µs waveforms. Thegreen columns are for four-wire and the orange for eight-wire conditions. Generally speaking,configuration one yields higher per-wire currents than configuration two and the four-wire test generateshigher currents than the eight-wire test. In most cases too, the 10/700-µs waveform yields higher peakcurrent with the exception of the eight-wire test in configuration two due to the maximum per-line seriesresistance of 250 Ω.

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Determining the Peak Surge Current www.ti.com




(1) For all eight lines, REQ is 31.3 Ω, which yields larger IPSC due to the maximum per-line series resistance of 250 Ω.

Table 3. Configuration One: Surge Applied From Lines to Ground (or Earth) With Other Lines Open

10/700 µsVPOC (V)

RGEN (Ω) REQ (Ω) 5/320 µsIPSC (A)

#Wires R4WIRE (Ω) #Wires R8WIRE (Ω) All fourlines

IPW-PSC (A)

Two of fourlines

IPW-PSC (A)

Two of fourlines

IPW-PSC (A)

All eightlines

IPW-PSC (A)

One ofeight linesIPW-PSC (A)

Two ofeight linesIPW-PSC (A)

500 15 25 12.50 4 100 8 200 3.13 4.35 3.85 1.56 2.33 2.171000 25.00 6.25 8.70 7.69 3.13 4.65 4.351500 37.50 9.38 13.04 11.54 4.69 6.98 6.522000 50.00 12.50 17.39 15.38 6.25 9.30 8.704000 100.00 25.00 34.78 30.77 12.50 18.60 17.396000 150.00 37.50 52.17 46.15 18.75 27.91 26.09

1.2/50 µsVPOC (V)

RGEN (Ω) REQ (Ω) (1) 8/20 µsIPSC (A) (1)


IPW-PSC (A)

One of fourlines

IPW-PSC (A)

Two of fourlines

IPW-PSC (A)

All eightlines

IPW-PSC (A)(1)



500 2 40 11.90 4 160 8 250 2.98 3.09 3.05 1.88 1.98 1.971000 23.81 5.95 6.17 6.10 3.76 3.97 3.941500 35.71 8.93 9.26 9.15 5.64 5.95 5.912000 47.62 11.90 12.35 12.20 7.52 7.94 7.874000 95.24 23.81 24.69 24.39 15.04 15.87 15.75

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www.ti.com Determining the Peak Surge Current




(1) For all eight lines, REQ is 31.3 Ω, which yields larger IPSC due to the maximum per-line series resistance of 250 Ω.

Table 4. Configuration Two: Surge Applied From Lines to Ground (or Earth) With Other Lines Grounded

10/700 µsVPOC (V)

RGEN (Ω) REQ (Ω) 5/320 µsIPSC (A)


IPW-PSC (A)

One of fourlines

IPW-PSC (A)

Two of fourlines

IPW-PSC (A)

All eightlines

IPW-PSC (A)



500 15 25 12.50 4 100 8 200 3.13 3.13 3.13 1.56 1.56 1.561000 25.00 6.25 6.25 6.25 3.13 3.13 3.131500 37.50 9.38 9.38 9.38 4.69 4.69 4.692000 50.00 12.50 12.50 12.50 6.25 6.25 6.254000 100.00 25.00 25.00 25.00 12.50 12.50 12.506000 150.00 37.50 37.50 37.50 18.75 18.75 18.75

1.2/50 µsVPOC (V)

RGEN (Ω) REQ (Ω) (1) 8/20 µsIPSC (A) (1)


IPW-PSC (A)

One of fourlines

IPW-PSC (A)

Two of fourlines

IPW-PSC (A)

All eightlines

IPW-PSC (A)(1)



500 2 40 11.90 4 160 8 250 2.98 2.98 2.98 1.88 1.88 1.881000 23.81 5.95 5.95 5.95 3.76 3.76 3.761500 35.71 8.93 8.93 8.93 5.64 5.64 5.642000 47.62 11.90 11.90 11.90 7.52 7.52 7.524000 95.24 23.81 23.81 23.81 15.04 15.04 15.04

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Determining the Peak Surge Current www.ti.com




For the PoE port front end, the SPDs are placed either across or from each center tap to ground (PSEframe or chassis, which is earth grounded). It should be noted that the capacitance associated with metaloxide varistors (MOVs) generally prevent them from being used on data lines because of their effect onsignal integrity. The centertap SPD will shunt twice the per-wire current and Table 5 and Table 6 combinethe per-wire currents into PoE center tap currents. Table 5 is a maximization of Table 3 and Table 4 foreach waveshape and Table 6 is a maximization of Table 4 only.

Table 5. Maximum Configuration One and Configuration Two Center-Tap Currents: 10/700 and1.2/50 Waveforms

VPOC (V) Four-line CMIPCT-PSC (A)

One-line DMIPCT-PSC (A)

Two-line DMIPCT-PSC (A)

Eight-line CMIPCT-PSC (A)



500 6.25 4.35 7.69 3.76 2.33 4.351000 12.50 8.70 15.38 7.52 4.65 8.701500 18.75 13.04 23.08 11.28 6.98 13.042000 25.00 17.39 30.77 15.04 9.30 17.394000 50.00 34.78 61.54 30.08 18.60 34.786000 75.00 52.17 92.31 37.50 27.91 52.17

Table 6. Maximum Configuration Two Center-Tap Currents: 10/700 and 1.2/50 Waveforms

VPOC (V) Four-line CMIPCT-PSC (A)



Eight-line CMIPCT-PSC (A)



500 6.25 3.13 6.25 3.76 1.88 3.761000 12.50 6.25 12.50 7.52 3.76 7.521500 18.75 9.38 18.75 11.28 5.64 11.282000 25.00 12.50 25.00 15.04 7.52 15.044000 50.00 25.00 50.00 30.08 15.04 30.086000 75.00 37.50 75.00 37.50 18.75 37.50

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PoE PSE (EUT)

R RRRRRRR

Combination WaveSurge Generator

Earth Ground

Return

Output

ALT A (MDI-X)

Isolation Boundary

IS

IH

IG

IF

IE

ID

IC

IB

IA

IRTN 1 IRTN 1+2+3+4

IRTN 1+2+3+4

IRTN 3

PoE PSE Testper

IEC 61000-4-5:2005

EthernetPhysicalDevice

TX

RX

1

2

3

6

4

5

7

8

Clamp

PSE / AC-DC Converter

Clamp

EMI Filter

TX

RX

Clamp

Clamp

Bob

Sm

ithT

erm

inat

ions

IRTN 2

IRTN 4

Logic GND

Logic GND to FRAME GND Connection

CBS

TVS 58V

MDI

FRAME

PSE Controller

www.ti.com PSE Surge Protection Application




4 PSE Surge Protection ApplicationMost (if not all) PSE applications will include a dedicated connection to earth ground as shown in Figure 4.Along with acting as a safety ground, this earth-ground connection might serve as a reference ground forinternal PSE circuitry, such as Bob Smith cable terminations and the primary-side of an isolated AC-DCconverter. These internal earth-ground connections can create paths for common-mode surge currents toflow from the generator, through the PSE, and back to the return of the generator as shown in Figure 4.

Referring to Figure 4, the surge current from the generator, IS, divides into the eight-wire input of the PSE,as indicated by current paths IA through IH. Once entering the PSE, the surge current will seek any pathsto earth ground in order to return to the generator. Two possible return paths are IRTN 1, through the BobSmith termination circuit block, and IRTN 4, through the isolated AC-DC converter circuit block. The mainconduits for these return paths are seen to be the highlighted CBS capacitor in the Bob Smith terminationblock and the typically used CCMB common-mode noise capacitor in the AC-DC converter block, each ofwhich crosses the isolation boundary. These two return paths and IRTN 2+3 are shown to combine as IRTN

1+2+3+4, which then returns back to the generator.

Figure 4. Example of Surge Current Paths Through Earthed-PSE Application

The currents as drawn in Figure 4 indicate a positive surge from the surge generator while, in actuality,the PSE will be subjected to five positive and five negative surges according to the IEC 61000-4-5 testprocedure. It should be noted that the surge current paths within each circuit block can vary depending onthe surge polarity. For example, during a positive surge some surge current will flow through the port TVSto the positive rail of the 48-V power supply, and during a negative surge some surge current will flowthrough the body diode of the port MOSFET.

The PSE controller block includes an EMI filter, which is normally required to meet conducted emissionsrequirements. This filter typically employs ferrite beads or a common-mode choke, which can help tolessen the amount of surge current flowing back to the converter. The PSE controller block is also shownto include a 58-V TVS that is typically placed across the port to protect against hot-plug transients andESD events. This TVS device will also contribute to the protection of the PSE controller during a lightningsurge.

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Choosing the SPDs for High Voltage Surge PSE Applications www.ti.com




Although this report focuses primarily on lightning surge protection for the front-end and power sections ofthe PSE, it should be noted that SPDs may require to be placed on the secondary-side data lines asindicated by the clamp blocks highlighted in Figure 4. Several manufacturers, such as Bourns™ andLittlefuse™, offer devices to protect the data lines. In order to maintain signal integrity, the type of deviceselected will normally depend on the capacitance associated with the device and the data rate of the PoEsystem. Consult the manufacturer’s datasheets for proper selection of these devices.

The requirements for SPDs in the PSE application will normally depend on the required surge test leveland the inherent isolation properties of the PSE. As previously described in Section 2, the IEEE 802.3standard specifies that the PSE must provide electrical isolation that withstands an electrical strength testof 1500 VRMS, 2250 VDC, or the 1500 VPK 10/700-µs impulse test defined in the IEC 60950-1 standard. Ifthe surge test level is below the inherent withstand strength of the PSE then additional SPDs may not beneeded. On the other hand, if the PSE will be subjected to surge test levels that exceed the withstandstrength of the PSE, then additional SPDs will most likely be required at the front-end of the PSE to eitherclamp the surge voltage below the withstand rating of the PSE or crowbar the surge to earth ground.

5 Choosing the SPDs for High Voltage Surge PSE ApplicationsThis section expands on the PSE example introduced in Section 4 by relating the actual requirement andselection of SPDs to the various test levels associated with the IEC 61000-4-5:2005 symmetrical linestest.

The SPD block is shown to be MOVs that are used to clamp the surge voltage to earth ground, whichcreates an added current path, IRTN 2, to return the surge current back to the generator when the MOVs areactivated. Each MOV would need to be capable of handling the combined currents of two lines. The actualnecessity for the MOVs will depend on the test level requirement and the withstand strength of the PSE.

This section will also discuss a four-port PSE application with each port defined to meet a different surgelevel. Table 7 shows the high-level requirement summary.

(1) The line-line can be implemented as a line-GND test for an unbalanced circuit or line.

Table 7. Requirements for Four-Port Design Example

PORT INSTALLATION CLASS

TEST LEVELS WAVEFORM (OCV-SCC)UNSYMMETRICALLY

OPERATED CIRCUITS ORLINES

SYMMETRICALLYOPERATED CIRCUITS OR

LINESCOUPLING MODE COUPLING MODE

LINE-TO-LINE ALL LINESTO GROUND

LINE-TO-LINE ALL LINESTO GROUND

4 2 NA 1000 NA 1000 10/700 µs to5/320 µs

1.2/50 µs to8/20 µs3 3 NA 2000 NA 2000

2 4 (1) 2000 4000 NA 40001 5++ NA 6000 NA 6000

The MOVs may not be required for test levels up to 1000 V because the IEEE 802.3 standard specifiesthat the PSE must have a withstand strength of at least 1500 VPK for the 10/700-µs impulse test. This isthe case for port 4 above and for this case the guidance provided in Electrical Transient Immunity forPower-Over-Ethernet[2] will be used. If the PSE port has been designed with a withstand rating per the1500 VRMS or 2250 VDC rating specified in the IEEE 802.3 standard then the MOVs may not be required forthe 2000-V test level. For this design example, MOVs will be used for port 3. The MOVs would definitelybe required to meet test levels that exceed the withstand strength of the PSE, which in most cases wouldinclude the 4000-V test level and certainly the 6000-V level. MOVs will be used also for port 1 and port 2to illustrate the design and selection procedure.

Although the MOVs might not be required to meet some of the lower test levels, implementing them for allconditions can lessen the stress on sensitive components within the AC-DC converter and add to theoverall robustness of the PSE. The intended operating environment of the PSE should be considered toassess the potential risk of damage and downtime of the PSE equipment versus the added cost of theprotection.

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www.ti.com Choosing the SPDs for High Voltage Surge PSE Applications




When selecting the proper MOV, its allowable operating voltage, maximum clamping voltage, and surgecurrent ratings need to be considered. Equally important is the repetitive surge capability (lifetime rating)of the MOV, since it will need to survive ten repetitions (five positive and five negative) during the test. Ingeneral the package size of the MOV will be directly proportional to its energy handling and surgecapability. While MOVs are available in a variety of package styles, this report concentrates on the use ofradial-leaded disc-type devices that are available in various diameters ranging from 5 mm to 20 mm.

As will be seen later, the MOVs chosen will provide a significantly higher lifetime rating than ten pulses asthis reference design will be subjected to a good deal of surge testing over and above the normal productsurge lifetime.

The general safety section of the IEEE 802.3 standard specifies that the PoE equipment shall conform tothe safety requirements of the IEC 60950-1 standard. Section 6.1.2 of this IEC standard states thefollowing regarding SPDs that are connected from telecommunications networks to earth:

6.1.2 Separation of the telecommunication network to earth6.1.2.1 RequirementsExcept as specified in 6.1.2.2, there shall be insulation between circuitry intended to be connectedto a telecommunications network and any parts or circuitry that will be earthed in someapplications, either within the EUT or via other equipment.Surge suppressors that bridge the insulation shall have a minimum rated operating voltage Uop(for example, the sparkover voltage of a gas discharge tube) ofUop = Upeak + ΔUsp + ΔUsawhere Upeak is one of the following values:for equipment intended to be installed in an area where the nominal voltage of the AC mainsexceeds 130 V: 360 Vfor all other equipment: 180 VΔUsp … shall be taken as 10% of the rated operating voltage of the component.ΔUsa … shall be taken as 10% of the rated operating voltage of the component.

Therefore, based on the above, the MOV used for the earthed PSE must have an allowable operatingvoltage of at least 216 VRMS when installed in an area where the nominal AC mains is less than 130 V andat least 432 VRMS when installed in an area where the nominal AC mains is greater than 130 V. This reportwill assume that the PSE is installed in an area where the nominal AC mains are less than 130 V, whichrequires an MOV with an allowable operating voltage of at least 230 VRMS (standard value).

It should be noted that the IEC 60950-1 standard allows insulation-bridging surge suppressors to beremoved during the steady-state electrical strength test of an SELV circuit. In conjunction with this, theIEEE 802.3 standard specifies that the Power Sourcing Equipment of the PoE system must not introducenon-SELV power into the PoE wiring plant, which would imply that the PSE is considered to be an SELVcircuit.

For this example, the current levels for the two-line differential mode (DM), four-wire CDN from Table 6 willbe used. The Littlefuse UltraMOV® Varistor Series was chosen based on availability and because of thedetailed repetitive surge capability curves within the device datasheet. The standard value for the 230VRMS rating was chosen (VxxE230P, where xx = disc diameter). The selection process continues by usingthe repetitive surge curves provided for each MOV size. The repetitive surge curves will indicate themaximum current versus pulse width rating of the MOV based on the number of expected surge pulses.For the IEC 61000-4-5:2005 test, the MOV will need to survive ten surge pulses with each current surgehaving an equivalent rectangular pulse width of 320 µs, which is based on the 320-µs time to half valueassociated with the 10/700-µs to 5/320-µs combination wave.

The Littlefuse V14E230P, V10E230P, and V07E230P were selected for port 1 (75 A), port 2 (50 A), andport 3 (25 A), respectively. For port 1 use a 320-µs impulse duration and 75-A surge current as shown inFigure 5 to get approximately 600 repetitions. This provides additional lifetime margin for extended testingand higher current levels such as those in Table 5. If the V10E230P is used at 320-µs impulse durationand 75-A surge current, the number of repetitions drops to approximately 30.

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75

620

75

320

600

Choosing the SPDs for High Voltage Surge PSE Applications www.ti.com




Figure 5. Using MOV Repetitive Surge Capability Curves

Continuing the example using V14E230P, the surge voltage between the center tap and ground during the75-A surge can be estimated using Figure 6.

Figure 6. Using the MOV Maximum Clamping Voltage Curves

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www.ti.com Reference Design




In order to finish the design for port 2 and port 3, go to the Littlefuse datasheet for V10E230P andV07E230P. For port 2 at 320-µs impulse duration and 50-A surge current, there are approximately 100repetitions, and for port 3 (25 A), there are 300 repetitions. The surge voltage at port 2 (50 A) and port 3(25 A) is 640 V and 630 V, respectively.

If the current waveform of the 1.2/50-µs to 8/20-µs combination wave generator sets the PSE surgerequirement, the MOV surge current requirement is reduced by approximately ten times. This requirementcan reduce the amount of PCB area and cost associated with the larger MOVs.

6 Reference DesignThis section covers the details of the four-port lightning surge reference design (PR2189E1). PR2189E1 isdesigned to meet the requirements of Table 7. Design goals include configuration as a typical customersystem including power, logic, and earth grounding, test points for measuring resultant surge voltages,isolated I2C communication, PHY side emulation to facilitate resultant surge voltage measurement, andPHY side protection options. The main design goal is to protect the PSE controller and PHY from damagedue to the surges. A stretch goal is to allow the system to ride through these surges without anynoticeable malfunctions. Key design features include:• Grounding

– System frame or earth ground-current shunting path for RJ45 housings– PoE or 54 VDC power ground from DC power supply– Logic or digital ground-may be connected to earth ground through resistors

• PCB spacings– > 80 mils from earth (and logic) ground (>4 kV based on 20 V/mil)– > 30 mils from Ethernet cable side nets (> 600 V)– > 20 mils from 54 VDC (VPWR) and port DRAINx nets

• SPDs– MOV as primary protection

• One from each PoE port center tap to (depends on surge voltage or current)• Two at DC power input feed to earth

– Per port TVS and clamping diodes-depends on surge voltage or current– Data line (PHY side) bidirectional TVS and transient current suppressor (TCS)

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MOV

Earth GND Lug

4+/-1kV

3+/-2kV

2+/-4kV

1+/-6kV

MOV MOVMOVMOV

+54VDCTPS23861

Logic GND Lug

PHY TP(4x)

PHY TP

USB-I2C

Non-metallic PCB standoffs (6x)

MOV MOV

Metallic HousingRJ45 (4x)

Reference Design www.ti.com




A graphical representation of PR2189E1 is shown in Figure 7. Four PoE ports are arranged along thebottom side with the corresponding PHY side ports at the top. The TPS23861 PSE controller is in themiddle and is managed over the isolation boundary by the USB-I2C host (if required). PoE 54 VDC input isprovided at the right side and provisions, such as MOVs and HV capacitors, bridging the isolationboundary are included to emulate the AC-DC converter in a PSE system.

Figure 7. PR2189E1 Reference Design Layout

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LOGOPCB

Texas Instruments

PR2189

E1

PCB Number:

PCB Rev:

Assembly NoteZZ1

These assemblies are ESD sensitive, ESD precautions shall be observed.

Assembly NoteZZ2

These assemblies must be clean and free fro m flux and all contaminants. Use of no clean flux is not acceptable.

Assembly NoteZZ3

These assemblies must comply with workmanship standards IPC-A-610 Class 2, unless otherwise specified.

Kelvin to port 3&4

22.1R11

47R9

47R7

47R1

47R12

22.1R14

22.1R4

22.1R8

VPWR

SEN3

DRN3

GATE3

DRN4

GATE4

SEN4

GATE2

DRN2

SEN2

GATE1

DRN1

SEN1

GND

GND

0.1µFC4

0.1µFC5

GND

VPWR

VDD1

RESET2

SCL3

SDAI4

SDAO5

INT6

DGND7

SEN3 8

DRAIN3 9

GATE3 10

KSENSB 11

SEN412

DRAIN413

GATE414

SEN1 15

DRAIN1 16

GATE1 17

KSENSA18

SEN219

DRAIN220

GATE221

AGND22

A323

SHTDWN24

AIN25

AOUT26

NC27

VPWR28

U2

TPS23861PW

58V

D1SMLJ58A

1

2

J1

ED555/2DS

I2C I/F

1 2

3 4

5 6

7 8

9 10

J2

N2510-6002-RB3.3V_USB

GND1

GNDGND

Kelvin to port 1&2

GND1

4.7kR18

0.1µFC11

0.1µFC10

10.0kR17

VCC11

OUTA2

INB3

GND14 GND2 5

OUTB6

INA7

VCC28

U4

ISO7221BD

3.3V3.3V_USB

0.1µF

C3

0.01µF

C1

1µF

C6

1µF

C9

3.3V

10.0kR5

1µFC7

L1

SDR0604-181KL

6.04kR13

4.99R6

47.5k

R2

13.3k

R10

200k

R3

4.7µF

C8

GND

1

2

4

3

U3

FOD817DS

GND1

4.7kR20

0.1µFC13

0.1µFC12

10.0kR19

3.3V3.3V_USB

GND

GND

10.0k

R15

10.0kR16

RTN1

VIN2

UVLO3

RON4

FB 5

VCC 6

BST7

SW8

EP9

U1

LM5019MRX/NOPB

H1

4820

H2

4820

H3

4820

H4

4820

VCC11

SDA12

SCL13

GND14

GND25

SCL2 6

SDA2 7

VCC28

U5

ISO1541D

J8

7693

0

R77

2200pFC54

2200pFC55

EARTH

EARTH

GND1

PRSTx

PSHDNx

PSCL

PSDA

PINTx

SHDNx

INTxRSTx

SDA

SCL

22µFC56

22µFC2

22µFC57

RV13 RV14

H5

4820

H6

4820

Clearance Constraint [Clearance = 20mil]TP1

4.7kR80





Figure 8. Schematic One

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Port1 Data

75.0

R25

75.0

R26

75.0

R27

75.0

R28

0.01µF

C15

0.01µF

C17

0.01µF

C19

0.01µF

C21

23

4

1

5

67

8

9

10

11

12

J3

EARTH

Clearance Constraint [Clearance = 80mil]

1000pF2000V

C22

12 3

4

L2

0.1µF

C14

0.1µF

C16

0.1µF

C18

0.1µF

C20

49.9R21

GND1

49.9R22

49.9R23

49.9R24

49.9R29

49.9R30

49.9R31

49.9R32

Port 1: Class 5+,+/-6kV

J5

7693

Gig Phy Terminators

Gig Phy Terminators

0.1µFC23

0.51R33

VPWR

DRN1

GATE1

SEN1

0.51R34

4

7,8

1,2

,3

5,6

,

100V

Q1FDMC3612

GND

D710MQ100NTRPBF

Kelvin to U1-18

58V

D6SMLJ58A

5VD5

CDSOD323-T05C

1CT:1

1CT:1

1CT:1

1CT:1

1

2

3

4

5

6

7

8

9

10

11

12 13

14

15

16

17

18

19

20

21

22

23

24

T1

PT61020EL

IN 11

NC2

OUT 13

OUT 24

NC5

IN 26

U9

TCS-DL004-250-WH

5VD4

CDSOD323-T05C

IN 1 1

NC2

OUT 13

OUT 24

NC5

IN 26

U8

TCS-DL004-250-WH

5VD3

CDSOD323-T05C

IN 11

NC2

OUT 13

OUT 24

NC5

IN 26

U7

TCS-DL004-250-WH

5VD2

CDSOD323-T05C

IN 11

NC2

OUT 13

OUT 24

NC5

IN 26

U6

TCS-DL004-250-WH

TP7

TP2

TP6

EARTH

Port2 Data

75.0

R39

75.0

R40

75.0

R41

75.0

R42

0.01µF

C25

0.01µF

C27

0.01µF

C29

0.01µF

C31

23

4

1

5

67

8

9

10

11

12

J6

EARTH

1000pF2000V

C32

12 3

4

L3

0.1µF

C24

0.1µF

C26

0.1µF

C28

0.1µF

C30

49.9R35

GND1

49.9R36

49.9R37

49.9R38

49.9R43

49.9R44

49.9R45

49.9R46

Port 2: Class 5,+/-4kV

Gig Phy Terminators

Gig Phy Terminators

0.1µFC33

0.51R47

VPWR

DRN2

GATE2

SEN2

0.51R48

4

7,8

1,2

,3

5,6

,

100V

Q2FDMC3612

GND

D1310MQ100NTRPBF

Kelvin to U1-18

58V

D12SMLJ58A

5VD11

CDSOD323-T05C

1CT:1

1CT:1

1CT:1

1CT:1

1

2

3

4

5

6

7

8

9

10

11

12 13

14

15

16

17

18

19

20

21

22

23

24

T2

PT61020EL

IN 11

NC2

OUT 13

OUT 24

NC5

IN 26

U13

TCS-DL004-250-WH

5VD10

CDSOD323-T05C

IN 1 1

NC2

OUT 13

OUT 24

NC5

IN 26

U12

TCS-DL004-250-WH

5VD9

CDSOD323-T05C

IN 11

NC2

OUT 13

OUT 24

NC5

IN 26

U11

TCS-DL004-250-WH

5VD8

CDSOD323-T05C

IN 11

NC2

OUT 13

OUT 24

NC5

IN 2 6

U10

TCS-DL004-250-WH

TP9

EARTH

5

4

1

23

67

8

J4

5

4

1

23

67

8

J7

Need 14mm MOV (V14E230P)


Center-tap protect ion total currentsMaximum current of Conf ig 1: 10/700 & 1.2/50 and Config 2: 10/700 & 1.2/50

4 Single Pair 8 Single PairVPOC(V) IPCT-PSC (A) IPCT-PSC (A) IPCT-PSC (A) IPCT-PSC (A) IPCT-PSC (A) IPCT-PSC (A)500 6.25 4.35 7.69 3.76 2.33 4.351000 12.50 8.70 15.38 7.52 4.65 8.701500 18.75 13.04 23.08 11.28 6.98 13.042000 25.00 17.39 30.77 15.04 9.30 17.394000 50.00 34.78 61.54 30.08 18.60 34.786000 75.00 52.17 92.31 37.50 27.91 52.17

The pair to pair surge generates the highest center-tap currentsGenerally config 1 yields higher currents than config 2The four line test generates higher currents than the eight line test

RV1

V14E230P

RV7

V10E230P

RV4

V14E230P

RV3

V14E230P

RV2

V14E230P

RV5

V10E230P

RV6

V10E230P

RV8

V10E230P

Do we want to provide spacing guidelines that depend on the expected voltage?

Based on 20V/mil?

1000V = 50 mil spacing

750V = 38 mil spacing

TP4

TP3

TP8

TP10

TP5

ClassName: 600V

ClassName: 600V

F1

B1250T

F2

B1250T

Reference Design www.ti.com




Figure 9. Schematic Two

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2

41

3

D24CD143A-SR70

Kelvin to U1-11

0.1µFC53

DRN4

GATE4

SEN4

0.51R75

0.51R76

4

7,8

1,2

,3

5,6

,

100V

Q4FDMC3612

12 3

4

L5

VPWR

F4

C1S 1.5

GND

Port 3: Class 3/4,+/-2kV

Port4 Data

75.0

R67

75.0

R68

75.0

R69

75.0

R70

0.01µF

C45

0.01µF

C47

0.01µF

C49

0.01µF

C51

2

3

4

1

5

6

7

8

9

1011

12

J12

EARTH

1000pF2000V

C52

0.1µF

C44

0.1µF

C46

0.1µF

C48

0.1µF

C50

49.9R63

GND1

49.9R64

49.9R65

49.9R66

49.9R71

49.9R72

49.9R73

49.9R74

Port 4: Class 2,+/-1kV

Gig Phy Terminators

Gig Phy Terminators

5VD23

CDSOD323-T05C

1CT:1

1CT:1

1CT:1

1CT:1

1

2

3

4

5

6

7

8

9

10

11

12 13

14

15

16

17

18

19

20

21

22

23

24

T4

PT61020EL

5VD22

CDSOD323-T05C

5VD21

CDSOD323-T05C

5VD20

CDSOD323-T05C

TP18

Port3 Data

75.0

R53

75.0

R54

75.0

R55

75.0

R56

0.01µF

C35

0.01µF

C37

0.01µF

C39

0.01µF

C41

23

4

1

5

67

8

9

10

11

12

J9

EARTH

1000pF2000V

C42

12 3

4

L4

0.1µF

C34

0.1µF

C36

0.1µF

C38

0.1µF

C40

49.9R49

GND1

49.9R50

49.9R51

49.9R52

49.9R57

49.9R58

49.9R59

49.9R60

Gig Phy Terminators

Gig Phy Terminators

0.1µFC43

0.51R61

VPWR

DRN3

GATE3

SEN3

0.51R62

4

7,8

1,2

,3

5,6

,

100V

Q3FDMC3612

F3

C1S 1.5

GND

D1910MQ100NTRPBF

Kelvin to U1-11

58V

D18SMLJ58A

5VD17

CDSOD323-T05C

1CT:1

1CT:1

1CT:1

1CT:1

1

2

3

4

5

6

7

8

9

10

11

12 13

14

15

16

17

18

19

20

21

22

23

24

T3

PT61020EL

IN 11

NC2

OUT 13

OUT 24

NC5

IN 26

U17

TCS-DL004-250-WH

5VD16

CDSOD323-T05C

IN 1 1

NC2

OUT 13

OUT 24

NC5

IN 26

U16

TCS-DL004-250-WH

5VD15

CDSOD323-T05C

IN 11

NC2

OUT 13

OUT 24

NC5

IN 26

U15

TCS-DL004-250-WH

5VD14

CDSOD323-T05C

IN 11

NC2

OUT 13

OUT 24

NC5

IN 26

U14

TCS-DL004-250-WH

TP16

TP13

TP15

EARTH

5

4

1

23

67

8

J10

54

1

2

3

6

7

8

J11


RV12

V07E230P

RV11

V07E230P

RV10

V07E230P

RV9

V07E230P

TP12

TP14

TP19

TP17

ClassName: 600V

ClassName: 600V

TP21





Figure 10. Schematic Three

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Test Report www.ti.com




7 Test ReportCommon mode:

(1) Surges applied to pair 1 and 2 followed by pair 3 and 6 using the surge generator in series with a 42-Ω resistor. Port tested is inforced ON state with DC disconnect disabled.

Port Detection status Class status Surge waveform Port on1 (1) Open circuit unknown ±6kV 1.2/50µs Pass2 Resistance valid Class 4 ±4kV 1.2/50µs Pass3 Resistance valid Class 4 ±2kV 1.2/50µs Pass4 Resistance valid Class 4 ±1kV 1.2/50µs Pass

Common mode:

(1) Surges applied to pair 1 and 2 followed by pair 3 and 6 using the surge generator in series with a 40-Ω resistor. Port tested is inforced ON state with DC disconnect disabled.

Port Detection status Class status Surge waveform Port on1 (1) Open circuit unknown ±6 kV 10/700 µs Pass2 (1) Open circuit unknown ±4 kV 10/700 µs Pass3 (1) Open circuit unknown ±2 kV 10/700 µs Pass4 (1) Open circuit unknown ±1 kV 10/700 µs Pass

Differential mode (single-wire differential):

(1) The surge generator used had ±4kV maximum capability.

Port Detection status Class status Surge waveform Port on1 (1) Resistance valid Class 4 ±4 kV 1.2/50 µs Pass2 Resistance valid Class 4 ±4 kV 1.2/50 µs Pass3 Resistance valid Class 4 ±2 kV 1.2/50 µs Pass4 Resistance valid Class 4 ±1 kV 1.2/50 µs Pass

Differential mode (single-pair differential):

(1) The surge generator used had ±4kV maximum capability.

Port Detection status Class status Surge waveform Port on1 (1) Resistance valid Class 4 ±4 kV 1.2/50 µs Pass2 Resistance valid Class 4 ±4 kV 1.2/50 µs Pass3 Resistance valid Class 4 ±2 kV 1.2/50 µs Pass4 Resistance valid Class 4 ±1 kV 1.2/50 µs Pass

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To PD Board

USB to GPIO

To PSE Port

From Power Supply

To PD Test Load

To PSE Port Surge is applied to each line

CDN

Generator

www.ti.com Test Report




Figure 11. Test Equipment

Figure 12. Test Setup

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Conclusion www.ti.com




8 ConclusionThis report has concentrated on the lightning surge requirements outlined for unshielded symmetrical linesaccording to the IEC 61000-4-5:2005 standard. The surge protection suggestions for the PSE have beenbased on applying a common-mode surge using the 10/700-µs to 5/320-µs combination wave generator inaccordance with the IEC standard. It should be noted that the surge protection requirements may bedifferent for PSE applications that require testing against other standards. In particular, attention must bepaid to the surge coupling method (common-mode or differential mode) and the equivalent pulse width ofthe surge current waveform when selecting the proper SPDs to meet a particular standard. In some cases,thyristors or gas discharge tubes may be used along with or instead of MOVs. The device choices mightbe based on surge handling capability or on acceptable PSE operation during the surge. In some casesthe PSE may be expected to seamlessly ride through a surge while in other cases a temporary glitch inoperation may be acceptable as long no damage is incurred. This report has adopted the use of MOVs inan effort to provide seamless operation of the PSE during a surge.

Although beyond the scope of this report, it should be understood that any lightning surge protectionsolution that is ultimately used for the PSE must also be compliant with any governing safety standards.For example, in some applications the PSE may be required to include input fuses to meet certain safetyrequirements related to power line cross. Aside from relating some of the references that the IEEE 802.3standard makes to the IEC 60950-1 standard, the suggestions provided in this report have been primarilyfocused on meeting the surge protection requirements of the PSE. The safety related requirements of thePSE will normally depend on its installation environment and possible user interface.

9 References1. Texas Instruments, Lightning Surge Considerations for PoE Powered Devices, Application Report

(SLUA736)2. Texas Instruments, Electrical Transient Immunity for Power-Over-Ethernet, Application Report

(SLVA233)3. IEEE 802.3at -20094. UL 60950-1:2007 standard (based on IEC 60950-1:2005), March 27, 20075. ITU-T Recommendation K.44, July, 20036. ITU-T Recommendation K.44 (Prepublication), April, 20087. IEC 61000-4-5:2005 standard, November, 2005

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http://www.ti.com/lit/pdf/SLUA736

http://www.ti.com/lit/pdf/SLVA233

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