RS485隔离参考设计

ApplicationReportSLLA299–October2009IsolatedRS-485ReferenceDesignThomasKugelstadt.........................................................................................ICP-IndustrialInterfaceThisdesignnotepresentsthereferencedesignsofisolatedRS-485nodes,usingbusvoltagesof3.3Vand5V.Varioustransceiversareusedtosatisfytherequirementsforlow,medium,andhighdatarates,aswellastoaccommodatetheneedforhalf-andfull-duplexoperation.Table1liststhefamilyofisolatedRS-485transceiversfromTexasInstruments.Table1.IsolatedRS-485TransceiversDataRateRiseTime[ns]Primary-SupplySecondary-SupplyDeviceTransmission[Mbps](Typical)VoltageRange[V]VoltageRange[V]ISO30820.29003.15–5.54.5–5.5ISO15Half-duplex11853.15–3.63.15–3.6ISO30882073.15–5.54.5–5.5ISO30800.29003.15–5.54.5–5.5ISO35Full-duplex11853.15–3.63.15–3.6ISO30862073.15–5.54.5–5.5Signal-PathIsolationAlltransceiverspresenta1/8unitloadtothebus,possessa4-kVpeakisolationvoltage,andhaveatypicaltransientimmunityof50kV/µs.WhereastheISO15andISO35(shadedcellsinTable1)operatefroma3.3-Vnominalsupplyonboththeprimarysideandthesecondaryside,thetransceiversoftheISO308xfamilyallowformixed-supplyoperation.Thisisofparticularadvantageforapplicationsoperatinginharshindustrialenvironments,becausethe3.3Vontheprimarysideenablestheconnectiontolow-voltagemicrocontrollersforpowerpreservation,whereasthe5Vonthesecondarysidemaintainsahighsignal-to-noiseratiowhendrivingsignalsacrosslongdistances.PowerSupplyIsolationModernisolatedpowersuppliesareavailableassmall,surface-mountmodules.Theyoftenincludethetransformerdriver,theactualisolationtransformer,andtherectifiernetwork.SophisticatedDC-DCmodules,suchastheRSZ-3.33.3HP(3.3Vin/3.3Vout)andRSZ-3.305HP(3.3Vin/5Vout),evenincludealinearregulatorwithitsassociatedbypassandoutputcapacitors,whileprovidingshort-circuitprotectionandasolid,2-kVisolationvoltage.NoiseandTransientSuppressionForeffectivetransientprotection,alow-capacitivetransientvoltagesuppressor(TVS),suchasPSM712,isrecommended.Thedeviceprovidesa600-Wsurgecapability,75pFofcapacitance,andupto40-kVESDprotection,whileitsstand-offvoltagescovertheRS-485common-moderangeof–7Vto+12V.Implementationofadditionalnoisefilteringtothesignalpathsbetweenthenodecontrollerandthesingle-endedsideofthetransceiverthroughsimpleR-Clow-passfiltersisrecommended.CalculatethefiltercomponentvaluessuchthatRF×CF=0.032/fSwithfSbeingthehighestsignalfrequencyofinterest.SystemDiagramsFigure1showsthesystemdiagramfora3.3-V/5-V,half-duplexnetworknodeusingISO3082forsignalisolationandRSZ-3.305HPforpowerisolation.Figure2showsthesystemdiagramfora3.3-V/3.3-V,full-duplexnetworknodeusingISO35forsignalisolationandRSZ-3.33.3HPforpowerisolation.1SLLA299–October2009IsolatedRS-485ReferenceDesignSubmitDocumentationFeedbackCopyright©2009,TexasInstrumentsIncorporatedRSZ-3.305HPREG436516TxDRxDGALVANICISOLATIONABDEDRREGND1GND2VCC1VCC22,7,89,10,15VDDDGNDDIR0VRF1RF2RF2CF1CF2CF20.1µF3.3V0V5V@200mAISO30820VISOXFMRDriveMSP4303.3µF214,5710.01µF0.01µFISO-Barrier1213ABRTNPSM712(600W)123References:•ForisolatedRS-485transceiverssee•ForisolatedDC-to-DCmodulessee•Fortransientvoltagesuppressorssee–October2009SubmitDocumentationFeedbackCopyright©2009,TexasInstrumentsIncorporatedRSZ-3.33.3HPREG4365141316TxDRxDGALVANICISOLATIONABDEDRREGND1GND2VCC1VCC22,7,89,10,15ABRTNVDDDGNDDIR0VRF1RF2RF2CF1CF2CF20.1µF3.3V0V3.3V@200mAISO350VISO2xPSM712123XFMRDriveMSP4303.3µF214,57YZ1112YZ12310.01µF0.01µFISO-Barrier–October2009IsolatedRS-485ReferenceDesignSubmitDocumentationFeedbackCopyright©2009,TexasInstrumentsIncorporatedIMPORTANTNOTICETexasInstrumentsIncorporatedanditssubsidiaries(TI)reservetherighttomakecorrections,modifications,enhancements,improvements,andotherchangestoitsproductsandservicesatanytimeandtodiscontinueanyproductorservicewithoutnotice.Customersshouldobtainthelatestrelevantinformationbeforeplacingordersandshouldverifythatsuchinformationiscurrentandcomplete.AllproductsaresoldsubjecttoTI’stermsandconditionsofsalesuppliedatthetimeoforderacknowledgment.TIwarrantsperformanceofitshardwareproductstothespecificationsapplicableatthetimeofsaleinaccordancewithTI’sstandardwarranty.TestingandotherqualitycontroltechniquesareusedtotheextentTIdeemsnecessarytosupportthiswarranty.Exceptwheremandatedbygovernmentrequirements,testingofallparametersofeachproductisnotnecessarilyperformed.TIassumesnoliabilityforapplicationsassistanceorcustomerproductdesign.CustomersareresponsiblefortheirproductsandapplicationsusingTIcomponents.Tominimizetherisksassociatedwithcustomerproductsandapplications,customersshouldprovideadequatedesignandoperatingsafeguards.TIdoesnotwarrantorrepresentthatanylicense,eitherexpressorimplied,isgrantedunderanyTIpatentr