BSN20应用(电平转换)

APPLICATIONNOTEBi-directionallevelshifterforI²C-busandothersystems.AN97055Bi-directionallevelshifterforI²C-busandothersystems.ApplicationNoteAN97055PhilipsSemiconductors2AbstractWithasingleMOS-FETabi-directionallevelshiftercircuitcanberealisedtoconnectdeviceswithdifferentsupplyvoltagesofe.g.5Voltand3.3VolttooneI2C-bussystem.Thelevelshiftercanalsoisolateabussectionofpowered-downdevicesfromtheI2C-bus,allowingthepoweredpartoftheI2C-bustooperateinanormalway.Thelevelshiftercanalsobeusedinotherbussystemsorpointtopointconnectionsforlevelshiftingand/orisolation.©PhilipsElectronicsN.V.1997Allrightsarereserved.Reproductioninwholeorinpartisprohibitedwithoutthepriorwrittenconsentofthecopyrightowner.Theinformationpresentedinthisdocumentdoesnotformpartofanyquotationorcontract,isbelievedtobeaccurateandreliableandmaybechangedwithoutnotice.Noliabilitywillbeacceptedbythepublisherforanyconsequenceofitsuse.Publicationthereofdoesnotconveynorimplyanylicenseunderpatent-orotherindustrialorintellectualpropertyrights.PurchaseofPhilipsI2CcomponentsconveysalicenseundertheI2Cpatenttousethecom-ponentsintheI2Csystem,providedthesystemconformstotheI2CspecificationsdefinedbyPhilips.Bi-directionallevelshifterforI²C-busandothersystems.ApplicationNoteAN97055PhilipsSemiconductors3APPLICATIONNOTEBi-directionallevelshifterforI²C-busandothersystems.AN97055Author:HermanSchuttePhilipsSemiconductorsSystemsLaboratoryEindhoven,TheNetherlandsKeywordsLevelshifter,bi-directional,I²C-bus,gateway,power-off,protection.Date:97-08-04Numberofpages:16Bi-directionallevelshifterforI²C-busandothersystems.ApplicationNoteAN97055PhilipsSemiconductors4SummaryPresenttechnologiesforintegratedcircuitwithclearancesof0.5μmandless,limitthemaximumsupplyvoltageandconsequentlythelogiclevelsforthedigitalI/Osignals.Tointerfacetheselowervoltagecircuitswithexisting5Voltdevicesalevelshifterisneeded.Forbi-directionalbussystemsase.g.theI2C-bus,suchalevelshiftermustbebi-directional,withouttheneedofadirectioncontrolsignal.WithonlyoneappropriateMOS-FETforeachbuslinethedesiredlevelshiftingwithautomaticdirectioncontrolcanbedone.Thelevelsmayhaveavastrange,dependingontheusedMOS-FET,e.g.downto2Voltatthe“Lowervoltage”sideandupto10Voltormoreatthe“Highervoltage”sideofthelevelshifter.Anadditionalfunctionofthelevelshifteristhatitcanisolateapowered-downsectioninabussystem,withoutobstructingthepoweredpart.Anotherfeatureistheprotectionofthe“Lowervoltage”sectionagainsthighvoltagespikesatthe“Highervoltage”section,aslongastheMOS-FETcanwithstandthisspikes.Bi-directionallevelshifterforI²C-busandothersystems.ApplicationNoteAN97055PhilipsSemiconductors5CONTENTS1.INTRODUCTION..........................................................................................................................................71.1References............................................................................................................................................71.2WorldWideWeb...................................................................................................................................72.INTERCONNECTIONOFDEVICESWITHDIFFERENTLOGICLEVELS...................................................82.1LogiclevelsoftheI2C-bus.....................................................................................................................82.2I2C-busdeviceswithdifferentsupplyvoltagesand5VtolerantI/O’s.......................................................92.3Deviceswithdifferentlogiclevelsconnectedviathebi-directionallevelshifter.....................................102.3.1Descriptionofthelevelshiftoperation.........................................................................................102.3.2Protectionofthe“Lowervoltage”sectionagainsthighvoltagespikes..........................................112.3.3Thelevelshifterusedinpointtopointconnections......................................................................112.3.4Isolationofthepowered-down“Lowervoltage”section...............................................................112.3.5Extendedcircuitforisolationofthepowered-down“highervoltage”section.................................123.CHARACTERISTICSOFTHEMOS-FET’S...............................................................................................134.WAVEFORMSOFTHELOGICLEVELS...................................................................................................144.1Shiftingfroma3Vtoa5Vlevel............................................................................................................144.2Shiftingfroma5Vtoa3Vlevel............................................................................................................154.3Waveformswhenabussectionispowered-down...............................................................................16Bi-directionallevelshifterforI²C-busandothersystems.ApplicationNoteAN97055PhilipsSemiconductors6Bi-directionallevelshifterforI²C-busandothersystems.ApplicationNoteAN97055PhilipsSemiconductors71.INTRODUCTIONTheI2C-bushasbeen