PROFIBUS Electrical-Layer Solutions (Rev. A)

1 1 IntroductionApplicationReportSLLA177A May2005 , ,suchassignalinglevels,buscapacitance,fa ulttolerance, (CH1)andB(CH2) (CMV).. ,whetherinprocessautomation,factoryautom ation,ormotioncontrol, ,referredtotheactuator/sensorlevel,thefi eldbusdirectlySLLA177A May2005 Level NetworksArea ControllerCell or Fieldbus NetworkHOSTCNCPCPCPLCPCF ieldbus ,thefieldorcelllevel, , , PROFIBUS wasestablishedasanationalstandard(DIN192 45) (EN50170). PROFIBUS wasadoptedinternationallyinIEC61158andIE C61784, ,thetermPROFIBUS hasbecomeabroadterm, ,theonlyPROFIBUS applicationwasPROFIBUSFMS(fieldmanagemen tsystem).

2 Now,otherapplicationssuchasPROFIBUSDP(1) (factoryautomation),PROFIBUSPA(processau tomation),andPROFI drive(motorcontrol) ,MBP(Manchesterencodingbuspowered),TIA/E IA-485(RS-485),orRS-485IS(intrinsicsafet y) , ,onemustunderstandthephysicallayerandhow thetransceiverispartofthatlayer.(1)Decen tralizedperipheralPROFIBUSE lectrical-LayerSolutions2 SLLA177A May2005 = 5 V 5%150 2%or 220 2%VP = 5 V 5%390 150 2%or 220 2%Up to 32 Devices;Transceivers, Drivers,Receivers, or Repeaters390 390 390 (VOD)+ VOD60 375 375 (PROFIBUSTestSpecificationsforPROFIBUSDP M asters, ,November2005andPROFIBUSTestSpecificatio nsforPROFIBUSDPS laves, ,November2005).

3 , resistoroveracommon-modevoltagerangeof 7 Vto12V, ,peak-to-peak(VOD(PP)) , ,meaningthattheactualvaluemeasuredinFigu re3canbeeither [ ( )]. , , , May2005 = 5 V 5%150 2%or 220 2%390 390 (1)To Bus+ VOD110 375 375 Common-ModeVoltage195 195 5 shouldonlybedonewhenthecharacteristicimp edanceofthecableislessthan125 [150||(390+390)].Aterminationresistancet hatislessthanthecharacteristicimpedanceo fthetransmissionlineresultsinnegativeref lections, pullupandpulldownresistorsaretheparallel equivalentofthe390- differentialimpedanceistheparallelcombin ationofthetwo220- , , ,thedrivermustovercometheoffsetinorderto meetthePROFIBUSDP testguidelines, May2005 (+, MIN)VIT (+, MAX)VIT ( , MAX)VIT ( , MIN)Noise MarginNoise MarginVOD (+, MIN)VOD (+, MAX)VOD ( , MAX)VOD ( , MIN)VOD = A-BVOD : Differential Output VoltageVIT.

4 Differential Input Theshold0 VOffset0 V+ VOD60 375 375 Common-ModeVoltage+ VOD110 375 375 Common-ModeVoltage195 195 5 V|VOD(+, MIN)| = V|VOD( , MAX)| = V|VOD(+, MIN)| = V|VOD( , MAX)| = V ,andassumingreceiverthresholdvoltagesof 200mVforVIT(-,MIN)(2)and+200mVforVIT(+,M AX)(3), ( ).However,ontherightside, , (min)foundinthedatasheetisdeterminedwith thebalancedcommon-modeloadinFigure3, (PP)requirementinthetestguidelinesandmai ntainasufficientamountofnoisemargininthe presenceofthePROFIBUS termination.(2)VIT :Negative-goingdifferentialinputvoltaget hreshold(3)VIT+:Negative-goingdifferenti alinputvoltagethresholdSLLA177A May2005 (CH1)andB(CH2) (>4V) (< ).

5 VOD(PP)=(A+ B ) (A B+)=( ) ( )= (between4 Vand7V). 7and+ (CMV)CMVCH1(A)CH1(A)CH2(B)CH2(B)Amplitud eAmplitudeVODVODVOHVOLVOHVOLSum(V)Differ ence(V)(peak-to-Offsetpeak) >4< <_< (Table100ofIEC61158-2),whichistobeusedwi ththeterminationfoundinFigure4whenthedif ferentialterminationis220 .Thecharacteristicimpedanceofthismediumc anrangefrom135 to165 (f=3 20 MHz).Theequivalentdifferentialterminatio nis171 ,andatypicalPROFIBUS cablehasacharacteristicimpedanceof150 .ThisreflectionaddstothealreadyhighVOD(P P)values,andinthenominal5-Vcase,theVOD(P P) ( ).

6 ,byallowingVccandcableimpedancetovarywit hinacceptablerangesfoundinboththe61158-2 standardandtransceiverdatasheets,acombin ationcanbefoundwhichviolatesthePROFIBUSD P testguidelines(seeTable2).LimitingVcctol essthan5V( )andchoosingacablethatiscloserto165- May2005 ConnectorBusBusTransceiver C orASICBus NodeSources of CapacitanceConnectorPCB TracesTransceiver (peak-to-peak)VOD(peak-to-peak) (kbps).Forexample,atasignalingrateof500k bps, ,stubs,anddevicesonthebus,butnotthecapac itanceofthecableitself(seeFigure9).Using theSN65 HVD1176asanexample,thenodecapacitance(4) calculationcouldbe10pF+20pF+2pF(device,c onnector,andstub).

7 , , (4)TheEN50170standarddoesnotmakeadistinc tionbetweendifferentialandsingle-endedca pacitance;however, , ,robustnessisthedegreetowhichatransceive rcanhandleelectricaloverstresses(EOS),wh ichcantaketheformofelectrostaticdischarg e(ESD),transientvoltage, May2005 VDCGNDRS485_VCCRS485_GNDF ilterRS485_GNDVPDGNDR egulatorDR010505SN65 HVD1176 Isolation BarrierRS485_VCCRS485_GNDRS485_VCCA LineB LineShieldRTS_TTLREDB9 ConnectorREIsolated DC/DC ConvertedPROFIBUS (AMR)ofthebuspinsisthemaximumvoltagethat canbeappliedwithaslowrisetime(sinewave) (ROC) ,theROCsforthebusI/Oareconsistentwiththe RS-485standard.

8 7 Vto+ , , , , May2005 = 1 to 50 MHzA = 5 V100 nFVoffset = 2 to 7 k 50 50 Scope470 nFABVCCGND100 k ,theideaofalargeabsolutemaximumratingand ,consequently,alargecommon-modevoltagera nge, , ,smallmagnitudeandlongduration, ,testmethodA114-A( ).Thisparticularstandarddefinesthehumanb odymodel(HBM). May2005 in AmperesTimeIR Peak to Peak RingingTRTDHigh VoltagePulseGeneratorRSR = 1500 DUTS ocket500 and Short+VCC16 VOutput16 VA and B ,theSN65 HVD1176usesprotectiondiodes, , May2005 ms100 Pulse Generator,15 s Duration1% Duty Cycle40 V 40 V15 (5)Thedurationissignificantlylongerthana nESDevent( svsns),andthevoltagelevelisdiminishedsig nificantly( 25 VvskV).

9 ThetransientovervoltagetestcircuitinFigu re14 ,thetestvoltagesare25 Vand ,theSN65 HVD1176canwithstandtransientovervoltages of , ,transientovervoltageprotection,andtheES Drating,themorerobusttheinterfaceis.(5) ,busterminationstobeused, , , , ,transientovervoltageprotection, May2005 |VOD| (min) (min) (min) (min)Buscapacitance(Cin)10pF(max)Notspec ified8pF(typical)NotspecifiedAbsolutemax imumratingofbuspinsAandB 9 Vto+14V 9 Vto+14V 8 Vto+13V 7 Vto+12 VTransientvoltageimmunity(6) 40 VNotspecifiedNotspecifiedNotspecifiedESD protection4kV(HBM)(7)NotspecifiedNotspec ified2kV(HBM)(2)Common-moderejection(CMR )4V(typical)NotspecifiedNotspecifiedNots pecified(6)TheRS485standardspecifiesamin imumvoltageimmunityof 25V.

10 Datasheetclaimsofstandardcomplianceimpli estheminimumrequirementalthoughnotexplic itlystatedinthedatasheet.(7)HBM= (SLLS563) +5 VLowPowerRS-485 PROFIBUST ransceiverDataSheet, ,MAX3460-MAX3464,+5V,Failsafe,20 Mbps,PROFIBUSRS-485/RS-422 Transceivers,Rev1, , Fieldbusforuseinindustrialcontrolsystems Part2:Physicallayerspecificationandservi cedefinition;IEC61158-2, ;EN50170 Volume2/3( PROFIBUS ), ,PROFIBUSI nternational, ,ElectricalCharacteristicsofGeneratorsan dReceiversforUseinBalancedDigitalMultipo intSystems, , , , ,November200512 PROFIBUSE lectrical-LayerSolutionsSLLA177A May2005 RevisedApril2006 SubmitDocumentationFeedbackIMPORTANT NOTICET exas Instruments Incorporated and its subsidiaries (TI) reserve the right to make corrections, modifications,enhancements, improvements, and other changes to its products and services at any time and to discontinueany product or service without notice.