QT18B20_ENG_v6

QT18B2018B20GNDDQVDD7QTechnologyDESCRIPTIONTheQT18B20digitalthermometerprovides9-bitto12-bitCelsiustemperaturemeasurementsandhasanalarmfunctionwithnonvolatileuser-programmableupperandlowertriggerpoints.TheQT18B20communicatesovera1-Wirebusthatbydefinitionrequiresonlyonedataline(andground)forcommunicationwithacentralmicroprocessor.Ithasanoperatingtemperaturerangeof-55°Cto+125°Candisaccurateto±0.5°Covertherangeof-10°Cto+85°C.Inaddition,theQT18B20canderivepowerdirectlyfromthedataline(“parasitepower”),eliminatingtheneedforanexternalpowersupply.EachQT18B20hasaunique64-bitserialcode,whichallowsmultipleQT18B20stofunctiononQT18B20ProgrammableResolution1-WireDigitalThermometerUser-DefinableNonvolatile(NV)AlarmSettingsAlarmSearchCommandIdentifiesandAddressesDevicesWhoseTemperatureisOutsideProgrammedLimitsAvailablein8-PinSO(150mils),8-PinµSOP,and3-PinTO-92PackagesApplicationsIncludeThermostaticControls,IndustrialSystems,ConsumerProducts,Thermometers,orAnyThermallySensitiveSystem2BytesUser-ProgrammableEEPROMESDRating:HBM8000V,MM800VPINCONFIGURATIONSthesame1-Wirebus.Thus,itissimpletouseonemicroprocessortocontrolmanyDS18B20sdistributedoveralargearea.ApplicationsthatcanbenefitfromthisfeatureincludeHVACenvironmentalcontrols,temperaturemonitoringsystemsinsidebuildings,equipment,orQT18B20123N.C.1N.C.2VDD3DQ48N.C.7N.C.6N.C.5GNDmachinery,andprocessmonitoringandcontrolsystems.FEATURES1-WireInterfaceRequiresOnlyOnePortPinforCommunicationEachDevicehasaUnique64-BitSerialCodeStoredinanOn-BoardROMMultidropCapabilitySimplifiesDistributedTemperature-SensingApplicationsRequiresNoExternalComponentsCanBePoweredfromDataLine;PowerSupply123SO(150mils)(QT18B20Z)µSOP(QT18B20U)Rangeis3.0Vto5.5VMeasuresTemperaturesfrom-55°Cto+125°C(-67°Fto+257°F)±0.5°CAccuracyfrom-10°Cto+85°CThermometerResolutionisUserSelectablefrom9to12BitsConvertsTemperatureto12-BitDigitalWordin750ms(Max)(BOTTOMVIEW)TO-92(QT18B20)1of22REV:061713QT18B202of22PINDESCRIPTIONPINNAMEFUNCTIONSOµSOPTO-921,2,6,7,82,3,5,6,7—N.C.NoConnection383VDDOptionalVDD.VDDmustbegroundedforoperationinparasitepowermode.412DQDataInput/Output.Open-drain1-Wireinterfacepin.Alsoprovidespowertothedevicewhenusedinparasitepowermode(seethePoweringtheQT18B20section.)541GNDGroundOVERVIEWFigure1showsablockdiagramoftheQT18B20,andpindescriptionsaregiveninthePinDescriptiontable.The64-bitROMstoresthedevice’suniqueserialcode.Thescratchpadmemorycontainsthe2-bytetemperatureregisterthatstoresthedigitaloutputfromthetemperaturesensor.Inaddition,thescratchpadprovidesaccesstothe1-byteupperandloweralarmtriggerregisters(THandTL)andthe1-byteconfigurationregister.Theconfigurationregisterallowstheusertosettheresolutionofthetemperature-to-digitalconversionto9,10,11,or12bits.Andthereare2-byteuserprogrammableEEPROM.TheTH,TL,configurationregisters,and2-byteuserprogrammableEEPROMarenonvolatile(EEPROM),sotheywillretaindatawhenthedeviceispowereddown.TheQT18B20uses1-Wirebusprotocolthatimplementsbuscommunicationusingonecontrolsignal.Thecontrollinerequiresaweakpullupresistorsincealldevicesarelinkedtothebusviaa3-stateoropen-drainport(theDQpininthecaseoftheQT18B20).Inthisbussystem,themicroprocessor(themasterdevice)identifiesandaddressesdevicesonthebususingeachdevice’sunique64-bitcode.Becauseeachdevicehasauniquecode,thenumberofdevicesthatcanbeaddressedononeQT18B203of22busisvirtuallyunlimited.The1-Wirebusprotocol,includingdetailedexplanationsofthecommandsand“timeslots,”iscoveredinthe1-WireBusSystemsection.AnotherfeatureoftheQT18B20istheabilitytooperatewithoutanexternalpowersupply.Powerisinsteadsuppliedthroughthe1-WirepullupresistorviatheDQpinwhenthebusishigh.Thehighbussignalalsochargesaninternalcapacitor(CPP),whichthensuppliespowertothedevicewhenthebusislow.Thismethodofderivingpowerfromthe1-Wirebusisreferredtoas“parasitepower.”Asanalternative,theQT18B20mayalsobepoweredbyanexternalsupplyonVDD.Figure1.QT18B20BlockDiagramVPU4.7kPARASITEPOWERCIRCUITMEMORYCONTROLLOGICQT18B20DQGNDVDDCPPINTERNALVDDPOWER-SUPPLYSENSE64-BITROMAND1-WirePORTSCRATCHPADTEMPERATURESENSORALARMTRIGGER(THTL)REGISTER(EEPROM)CONFIGURATIONREGISTER(EEPROM)2-byteUserByte(EEPROM)8-BITCRCGENERATOROPERATION—MEASURINGTEMPERATUREThecorefunctionalityoftheQT18B20isitsdirect-to-digitaltemperaturesensor.Theresolutionofthetemperaturesensorisuser-configurableto9,10,11,or12bits,correspondingtoincrementsof0.5°C,0.25°C,0.125°C,and0.0625°C,respectively.Thedefaultresolutionatpower-upis12-bit.TheQT18B20powersupinalow-poweridlestate.ToinitiateatemperaturemeasurementandA-to-Dconversion,themastermustissueaConvertT[44h]command.Followingtheconversion,theresultingthermaldataisstoredinthe2-bytetemperatureregisterinthescratchpadmemoryandtheQT18B20returnstoitsidlestate.IftheQT18B20ispoweredbyanexternalsupply,themastercanissue“readtimeslots”(seethe1-WireBusSystemsection)aftertheConvertTcommandandtheQT18B20willrespondbytransmitting0whilethetemperatureconversionisinprogressand1whentheconversionisdone.IftheQT18B20ispoweredwithparasitepower,thisnotificationtechniquecannotbeusedsincethebusmustbepul