STM32晶振设计指南Oscillator-design-guide-for-STM8S-STM8A

December2014DocID15287Rev81/401AN2867ApplicationnoteOscillatordesignguideforSTM8S,STM8AandSTM32microcontrollersIntroductionMostdesignersarefamiliarwithoscillators(Pierce-Gatetopology),butfewreallyunderstandhowtheyoperate,letalonehowtoproperlydesignanoscillator.Inpractice,mostdesignersdonotevenreallypayattentiontotheoscillatordesignuntiltheyrealizetheoscillatordoesnotoperateproperly(usuallywhenitisalreadybeingproduced).Thisshouldnothappen.Manysystemsorprojectsaredelayedintheirdeploymentbecauseofacrystalnotworkingasintended.Theoscillatorshouldreceiveitsproperamountofattentionduringthedesignphase,wellbeforethemanufacturingphase.Thedesignerwouldthenavoidthenightmarescenarioofproductsbeingreturned.ThisapplicationnoteintroducesthePierceoscillatorbasicsandprovidessomeguidelinesforagoodoscillatordesign.ItalsoshowshowtodeterminethedifferentexternalcomponentsandprovidesguidelinesforagoodPCBfortheoscillator.Thisdocumentfinallycontainsaneasyguidelinetoselectsuitablecrystalsandexternalcomponents,anditlistssomerecommendedcrystals(HSEandLSE)forSTM32andSTM8A/Smicrocontrollersinordertoquickstartdevelopment.RefertoTable1forthelistofapplicableproducts.Table1.ApplicableproductsTypeProductsub-classesMicrocontrollersSTM8SSeriesSTM8AFSeries,STM8ALSeriesSTM3232-bitARMCortexmicrocontrollers(DL)andexternalresistor(RExt)calculation.............153.5.1Calculatingdrivelevel(DL)..................................153.5.2Anotherdrivelevelmeasurementmethod.......................163.5.3Calculatingexternalresistor(RExt)............................163.6Startuptime...............................................173.7Crystalpullability...........................................174Guidelinesforselectingsuitablecrystalandexternalcomponents....................................194.1Low-speedoscillatorsembeddedintoSTM32microcontrollers........194.2DetailedstepstoselectanSTM32-compatiblecrystal...............225SomerecommendedresonatorsforSTM32microcontrollers.....................................255.1STM32-compatiblehigh-speedresonators.......................255.2STM32-compatiblelow-speedresonators........................266SomerecommendedcrystalsforSTM8A/Smicrocontrollers.......286.1Partnumbersofrecommendedcrystaloscillators..................286.2Partnumbersofrecommendedceramicresonators................28DocID15287Rev83/40AN2867Listoftables37Tipsforimprovingoscillatorstability..........................297.1PCBdesignguidelines......................................297.2PCBdesignexamples.......................................317.3Solderingguidelines.........................................358Referencedocuments.......................................369Conclusion................................................3710Revisionhistory...........................................38ListoftablesAN28674/40DocID15287Rev8ListoftablesTable1.Applicableproducts.......................................................1Table2.Exampleofequivalentcircuitparameters.......................................7Table3.Typicalfeedbackresistorvaluesforgivenfrequencies...........................12Table4.LSEoscillatorsembeddedintoSTM32microcontrollers..........................21Table5.HSEoscillatorsembeddedinSTM32microcontrollers............................25Table6.LSEoscillatorsembeddedinSTM32microcontrollers............................27Table7.KYOCERA.............................................................28Table8.Recommendableconditions(forconsumer)....................................28Table9.Recommendableconditions(forCAN-BUS)....................................28Table10.Documentrevisionhistory.................................................38DocID15287Rev85/40AN2867Listoffigures5ListoffiguresFigure1.Quartzcrystalmodel.......................................................6Figure2.Impedancerepresentationinthefrequencydomain...............................6Figure3.I-Vcurveofadipoleshowinganegativetransresistancearea(inpurple)..............9Figure4.Blockdiagramofatypicaloscillationloopbasedonacrystalresonator..............10Figure5.Pierce-oscillatorcircuitry...................................................11Figure6.Invertertransferfunction...................................................12Figure7.Currentdrivemeasurementwithacurrentprobe................................15Figure8.Class