温度传感器 DS18B20-PAR 详细资料

1of19043001FEATURES•Unique1-wireinterfacerequiresonlyoneportpinforcommunication•Derivespowerfromdataline(“parasitepower”)—doesnotneedalocalpowersupply•Multi-dropcapabilitysimplifiesdistributedtemperaturesensingapplications•Requiresnoexternalcomponents•±0.5°Caccuracyfrom–10°Cto+85°C•Measurestemperaturesfrom–55°Cto+100°C(–67°Fto+212°F)•Thermometerresolutionisuser-selectablefrom9to12bits•Convertstemperatureto12-bitdigitalwordin750ms(max.)•User–definablenon-volatiletemperaturealarmsettings•Alarmsearchcommandidentifiesandaddressesdeviceswhosetemperatureisoutsideofprogrammedlimits(temperaturealarmcondition)•SoftwarecompatiblewiththeDS1822-PAR•Idealforuseinremotesensingapplications(e.g.,temperatureprobes)thatdonothavealocalpowersourcePINASSIGNMENTPINDESCRIPTIONGND-GroundDQ-DataIn/OutNC-NoConnectDESCRIPTIONTheDS18B20-PARdigitalthermometerprovides9to12–bitcentigradetemperaturemeasurementsandhasanalarmfunctionwithnonvolatileuser-programmableupperandlowertriggerpoints.TheDS18B20-PARdoesnotneedanexternalpowersupplybecauseitderivespowerdirectlyfromthedataline(“parasitepower”).TheDS18B20-PARcommunicatesovera1-wirebus,whichbydefinitionrequiresonlyonedataline(andground)forcommunicationwithacentralmicroprocessor.Ithasanoperatingtemperaturerangeof–55°Cto+100°Candisaccurateto±0.5°Coverarangeof–10°Cto+85°C.EachDS18B20-PARhasaunique64-bitidentificationcode,whichallowsmultipleDS18B20-PARstofunctiononthesame1–wirebus;thus,itissimpletouseonemicroprocessortocontrolmanyDS18B20-PARsdistributedoveralargearea.ApplicationsthatcanbenefitfromthisfeatureincludeHVACenvironmentalcontrols,temperaturemonitoringsystemsinsidebuildings,equipmentormachinery,andprocessmonitoringandcontrolsystems.DS18B20-PAR1-Wire®Parasite-PowerDigitalThermometer(DS18B20-PAR)1(BOTTOMVIEW)23DALLAS18B20P1GNDDQNC23DS18B20-PAR2of19DETAILEDPINDESCRIPTIONSTable1PINSYMBOLDESCRIPTION1GNDGround.2DQDataInput/Outputpin.Open-drain1-wireinterfacepin.Alsoprovidespowertothedevicewhenusedinparasitepowermode(see“ParasitePower”section.)3NCNoConnect.Doesn’tconnecttointernalcircuit.OVERVIEWTheDS18B20-PARusesDallas’exclusive1-wirebusprotocolthatimplementsbuscommunicationusingonecontrolsignal.Thecontrollinerequiresaweakpullupresistorsincealldevicesarelinkedtothebusviaa3-stateoropen-drainport(theDQpininthecaseoftheDS18B20-PAR).Inthisbussystem,themicroprocessor(themasterdevice)identifiesandaddressesdevicesonthebususingeachdevice’sunique64-bitcode.Becauseeachdevicehasauniquecode,thenumberofdevicesthatcanbeaddressedononebusisvirtuallyunlimited.The1-wirebusprotocol,includingdetailedexplanationsofthecommandsand“timeslots,”iscoveredinthe1-WIREBUSSYSTEMsectionofthisdatasheet.AnimportantfeatureoftheDS18B20-PARisitsabilitytooperatewithoutanexternalpowersupply.Powerisinsteadsuppliedthroughthe1-wirepullupresistorviatheDQpinwhenthebusishigh.Thehighbussignalalsochargesaninternalcapacitor(CPP),whichthensuppliespowertothedevicewhenthebusislow.Thismethodofderivingpowerfromthe1-wirebusisreferredtoas“parasitepower.”Figure1showsablockdiagramoftheDS18B20-PAR,andpindescriptionsaregiveninTable1.The64-bitROMstoresthedevice’suniqueserialcode.Thescratchpadmemorycontainsthe2-bytetemperatureregisterthatstoresthedigitaloutputfromthetemperaturesensor.Inaddition,thescratchpadprovidesaccesstothe1-byteupperandloweralarmtriggerregisters(THandTL).TheTHandTLregistersarenonvolatile(EEPROM),sotheywillretaintheirdatawhenthedeviceispowereddown.DS18B20-PARBLOCKDIAGRAMFigure1CPPVPU4.7K64-BITROMAND1-wirePORTDQINTERNALVDDPARASITEPOWERCIRCUITMEMORYCONTROLLOGICSCRATCHPAD8-BITCRCGENERATORTEMPERATURESENSORALARMHIGHTRIGGER(TH)REGISTER(EEPROM)ALARMLOWTRIGGER(TL)REGISTER(EEPROM)CONFIGURATIONREGISTER(EEPROM)GNDDS18B20-PARDS18B20-PAR3of19PARASITEPOWERTheDS18B20-PAR’sparasitepowercircuitallowstheDS18B20-PARtooperatewithoutalocalexternalpowersupply.Thisabilityisespeciallyusefulforapplicationsthatrequireremotetemperaturesensingorthatareveryspaceconstrained.Figure1showstheDS18B20-PAR’sparasite-powercontrolcircuitry,which“steals”powerfromthe1-wirebusviatheDQpinwhenthebusishigh.ThestolenchargepowerstheDS18B20-PARwhilethebusishigh,andsomeofthechargeisstoredontheparasitepowercapacitor(CPP)toprovidepowerwhenthebusislow.The1-wirebusandCPPcanprovidesufficientparasitepowertotheDS18B20-PARformostoperationsaslongasthespecifiedtimingandvoltagerequirementsaremet(refertotheDCELECTRICALCHARACTERISTICSandtheACELECTRICALCHARACTERISTICSsectionsofthisdatasheet).However,whentheDS18B20-PARisperformingtemperatureconversionsorcopyingdatafromthescratchpadmemorytoEEPROM,theoperatingcurrentcanbeashighas1.5mA.Thiscurrentcancauseanunacceptablevoltagedropacrosstheweak1-wirepullupresistorandismorecurrentthancanbesuppliedbyCPP.ToassurethattheDS18B20-PARhassufficientsupplycurrent,itisnecessarytoprovideastrongpulluponthe1-wirebuswhenevertemperatureconversionsaretakingplaceordataisbeingcopiedfromthescratchpadtoEEPROM.ThiscanbeaccomplishedbyusingaMOSFETtopullthebusdirectlytotherailasshowninFigure2.The1-wirebusmustbeswitchedtothestrongpullupwithin10µs(max)af