RClamp0512TQ
Final Datasheet Rev 6.0
December 17, 2015
www.semtech.com Page 7
Semtech
Application Information
Figure 1 - 1GbE / 2.5GbE Protection Circuit
1
2
3
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8
5
6
7
RJ-45
Ethernet PHY
1GbE / 2.5GbE
RClamp0512TQ
RClamp0512TQ
RClamp0512TQ
RClamp0512TQ
1
2
3
1
2
3
1
2
3
1
2
3
intheprotectionpathshouldbeminimizedbylocating
RClamp0512TQasphysicallyclosetothemagneticsas
possible,andpreferablyonthesamesideofthePCB.
Reducingparasiticinductanceisespeciallyimportant
forsuppressingfastrisetimetransientssuchasESDand
EFT.Inductanceinthepathoftheprotectiondevice
increasesthepeakclampingvoltageseenbytheprotect-
eddevice(V=Ldi/dt).Forexample,1nHofinductance
canincreasethepeakclampingvoltageby30Vfora30A
(8kV)ESDpulsewitha1nsrisetime.Dierentialpairsare
routedthrougheachRClamp0512TQatpins1and2.Pin
3ofthedeviceisnotconnected.
PlacingtheprotectiononthePHYsideofthemagnetics
isadvantageousinthatthemagnitudeanddurationof
thesurgeisattenuatedbythetransformerwindings.The
amountofattenuationwillvarybyvendorandcong-
urationofthemagnetics.TheEthernettransformerhas
tobeabletosupporttheimpulsetestswithoutfailure.
AtypicalEthernettransformercanwithstandafew
hundredamperes(tp=8/20us)beforefailureoccurs,but
thisneedstobeveriedbytesting.Alternatively,the
protectioncanbeplacedonthelinesideofthetrans-
former.However,theadditionalprotectionaordedby
thetransformerislost,andtheabilityofthesystemto
withstandhighenergysurgesislimitedtothecapability
oftheprotectiondevice.
Ethernet Protection
Ethernetportsareexposedtoexternaltransientevents
intheformofESD,EFT,lightning,andcabledischarge
events(CDE).Teststandardsthatmodeltheseevents
includeIEC61000-4-2forESD,IEC61000-4-4forEFT,and
IEC61000-4-5andGR-1089forlightning.Anyofthese
eventscancausecatastrophicdamagetothePHYIC.
WhendesigningEthernetprotection,theentiresys-
temmustbeconsidered.Over-voltageeventscanbe
commonmode(withrespecttoground)ordieren-
tial(line-to-line).AnEthernetportincludesinterface
magneticsconsistingoftransformersintegratedwith
commonmodechokes.Thetransformercentertapsare
connectedtogroundviaanRCnetworkor“BobSmith”
termination.Thepurposeofthisterminationistoreduce
commonmodeemissions.Thetransformerprovides
commonmodeisolationtotransientevents,butno
protectionfordierentialsurges.Duringadierential
transientevent,currentwillowthroughthetransform-
er,chargingthewindingsonthelineside.Energyis
transferredtothesecondaryuntilthesurgesubsidesor
thetransformersaturates.
Atypicalprotectionschemewhichutilizesthe
RClamp0512TQisshowninFigure1.Thedevicesare
locatedonthePHYsideofthetransformerwithone
deviceplacedacrosseachlinepair.Parasiticinductance