application note: an2093 · ground circuit that is shared by all of the components ... application...
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2111 Comprehensive Drive
Aurora, Illinois 60505
Phone: 630-851-4722
Fax: 630- 851- 5040
www.conwin.com
Application Note AN2093Page
1Revision P02Date 18 April 2018
OCXO Layout Guidelines
Application Note AN2093Page 1 Revision P01Date 10 May 2013
1.1 Introduction
Thetechniquesincludedinthisapplicationnotewillhelptoensuresuccessfulprintedcircuitboardlayoutusinganoven-controlledcrystaloscillator(OCXO).Problemswithlayoutcanresultinnoisyanddistortedfrequencytransmissions,error-pronedigitalcommunications,latch-upproblems,significantlyreducedfrequencystability,thermalinstabilitywithintheOCXO,andotherundesirablesystembehavior.
1.2 This document includes the following • Powerandgroundcircuitdesigntips. • Theoryofoperation/Characterization • Techniquestoachieveoptimalthermalconditionsusingmultilayerboards • Adesignchecklist
1.3 About this document
ThemethodspresentedinthisapplicationnoteshouldbetakenassuggestionswhichprovideagoodstartingpointinthedesignandlayoutofaPCB.Itshouldbenotedthatonedesignruledoesnotnecessarilyfitalldesigns.ItishighlyrecommendedthatprototypePCBsbemanufacturedtotestdesigns.
ForfurtherinformationpleasecontactConnor-WinfieldEngineeringDepartment.
Application Note: AN2093
Section 1: About this document.
Specifications subject to change without notice. All dimensions in inches. © Copyright 2012 The Connor-Winfield Corporation
2111 Comprehensive Drive
Aurora, Illinois 60505
Phone: 630-851-4722
Fax: 630- 851- 5040
www.conwin.com
Application Note: AN2093 Page 2 of 20 Rev: P02 Date: 04/18/18© Copyright 2018 The Connor-Winfield Corp. All Rights Reserved Specifications subject to change without notice
All Rights Reserved. See website for latest revision. Not intended for life support applications.
2111 Comprehensive Drive
Aurora, Illinois 60505
Phone: 630-851-4722
Fax: 630- 851- 5040
www.conwin.com
Specifications subject to change without notice. All dimensions in inches. © Copyright 2012 The Connor-Winfield Corporation
Section 2: Power & Ground Considerations.
2.1 Power Supply and Grounds. Allsystemdesignshaveapowersupplyandgroundcircuitthatissharedbyallofthecomponentsontheboard.Theoperationofonecomponentcanaffecttheoperationofothercomponentsthatsharethesamepowersupplyandgroundcircuit.
2.2 Power Supply. Thegoalofasystem’spowersupplyistomaintainastablevoltagewithinaspecifiedrangewhilesupplyingsufficientcurrent.Whileanidealpowersupplywouldmaintainthesamevoltageforanypossiblecurrentdraw,realworldsystemsexhibitthefollowingbehaviors:
• Achangeincurrentanditsassociated noisecausedbyonedeviceaffectsother devicesattachedtothesamepowersupply net.• Achangeincurrentdrawaffectsthevoltage ofthepowernet.
2.3 Typical Power Supply System. Atypicalpowersupplycircuitconsistsofthefollowing:
• Voltageregulatorsthatmaintainvoltage stabilitywithinarequiredrangewhile supplyingsufficientcurrenttoallcomponents served.• Bulk,decouplingandbypasscapacitors.• Powerandsupplycircuitrunnersorpower supplyplanesforpowerdistributionto components.• Localdecouplingandbypasscapacitorsat eachsupplysensitivecomponent.
2.4 Power Supply Management. Impropervoltageregulationcanresultininstabilityofmanysystemcomponentsorcompletesystemfailure. Periodsofinsufficientpowerareoftenreferredtoas“Brown-Outs”,wherepowersupplyvoltagedropstoaninsufficientlevel,or“Black-Outs”wherepowersupplyvoltagestotallydisappearforaperiodoftime.
FortheOCXOtopowerupandconfigureproperlyoninitialpower-up,Vccmustexceedthemaximumpower-onreset(VPOR)voltageinorderforthedevicetoproceedwithconfigurationandinitialization.TheVCCvoltageisinternallymonitoredonpower-uptoproperlytriggerthedeviceconfigurationcircuitry. Onsubsequentbrown-outconditionswherethedeviceisnotpower-cycled(i.e.,thesupplyvoltagesarenottakedownto0v),theVccvoltagemustbetakendownbelowtheminimumVPORvoltageinordertoclearoutthedeviceconfigurationcontent.Subsequently,thevoltagesmustexceedtheVPORvoltageonceagaininorderforthedevicetobeprogrammedwiththenewconfiguration. Abrown-outconditionisdefinedbytheVccraildroppingbelowitsrespectivedataretentionvoltagedefinedbytheVRAMinthedatasheet. PleaserefertotheOCXOdatasheetfortheminimumandmaximumVPORvoltagesandDataRetentionVoltages. Preventsystemmalfunctionduringperiodsofinsufficientpowersupplyvoltagebyusingexternallowervoltagedetectorlogicandsupplymanagementcircuitry.
2.5 POR/BOR Operation. Thepower-onresetoccurswhenthedeviceisstartedfromaVsslevel.Thebrown-outconditionoccurswhenapreviouslypowereddevicedropsbelowaspecifiedrange. ThedevicesRAMretentionvoltage(VRAM)islowerthantheVPOR/VBORvoltagetrippoint.WhenVPRO/VBOR<Vcc<2.7V,theelectricalperformanceoftheOCXOwillNOTmeetthedatasheetspecifications.2.6 Power-on Reset. Whenthedevicepowersup,thedeviceVccwillcrosstheVPOR/VBORvoltage.OncetheVccvoltagecrossestheVPOR/VBORvoltagethefollowingwilloccur: • Volatileregistersareloadedwith valuesformthecorresponding non-volatileregisters. • TheTCONFregisterwillloadthefactory programming. • ThedeviceiscapableofDigital/Analog operation.
Application Note AN2093Page 2Revision P01Date 10 May 2013
Application Note: AN2093 Page 3 of 20 Rev: P02 Date: 04/18/18© Copyright 2018 The Connor-Winfield Corp. All Rights Reserved Specifications subject to change without notice
All Rights Reserved. See website for latest revision. Not intended for life support applications.
Specifications subject to change without notice. All dimensions in inches. © Copyright 2012 The Connor-Winfield Corporation
2111 Comprehensive Drive
Aurora, Illinois 60505
Phone: 630-851-4722
Fax: 630- 851- 5040
www.conwin.com
2.7 Brown-Out Reset. Whenthedevicepowersdown,thedeviceVccwillcrosstheVPOR/VBORvoltage.OncetheVccvoltagedecreasesbelowtheVPOR/VBORvoltagethefollowingoccurs: • Factoryserialprogramminginterfaceis disabled. • Non-Volatileregisterarenolonger programmable.
IftheVCCvoltagedecreasesbelowtheVRAMvoltagethefollowingoccurs: • Volatileregistersmaybecomecorrupted. • TCONFregistermaybecomecorrupted. • OCXOovencoremaylosethermal equilibrium. • OCXOfrequencystabilitymaynotmeetthe datasheetspecifications. AsthevoltagerecoversabovetheVPOR/VBORvoltageseesection“Power-onReset”Onsubsequentbrown-outconditionswherethedeviceisnotpower-cycledproperly(i.e.,thesupplyvoltagesarenottakendownto0V),thepowersupplyvoltagemustbedroppedbelow1.6voltsinordertoclearouttheEEPROMdeviceconfigurationcontent.
2 8 Voltage Regulators. Avoltageregulatortakesaninputvoltagefromanexternalsourceandstepsitdowntoasuitablevoltagelevelthatcanpowercomponentsonthecircuitboard.Twocommontypesofvoltageregulatorsaredc-dcconvertersandlow-dropoutregulators(LDO).Whendecidingonavoltageregulator,alwaysreviewtheregulatordatasheetstomatchcomponentspecificationswithsystemrequirements. AsdigitallogicgatesofICsswitchfromonestatetoanother,theIC’scurrentdrawfluctuatesatafrequencydeterminedbythelogicstatetransitionrateor“rise-time”.Thesecurrentoscillationscausethepowersupplyvoltagetofluctuateasasmallvoltagedevelopsacrossthenetduetoitsintrinsicimpedance.Thecircuit’simpedancecanbeloweredbycarefullyselectingacapacitorthatprovidesalow-impedancepathtogroundforhighfrequencies.Asacapacitorchargesordischargescurrentflowsthroughitwhichitselfisrestrictedbytheinternalresistanceofthecapacitor.ThisinternalresistanceisknownasCapacitiveReactanceandisgiventhesymbolXCinohms.Unlikeresistancewhichhasafixedvalue,ie100Ω,1kΩ,etc.CapacitiveReactancevarieswithfrequencysoanyvariationinfrequencywillhaveaneffectonthecapacitor.Theloopfromthevoltagesupplypintodecouplingcapacitortogroundshouldbekeptassmallaspossiblebyplacingthecapacitornearthepowersupplypinandgroundpinofthedevice.
Application Note AN2093Page 3Revision P01Date 10 May 2013
Section 2: Power & Ground Considerations continued
Application Note: AN2093 Page 4 of 20 Rev: P02 Date: 04/18/18© Copyright 2018 The Connor-Winfield Corp. All Rights Reserved Specifications subject to change without notice
All Rights Reserved. See website for latest revision. Not intended for life support applications.
Specifications subject to change without notice. All dimensions in inches. © Copyright 2012 The Connor-Winfield Corporation
2111 Comprehensive Drive
Aurora, Illinois 60505
Phone: 630-851-4722
Fax: 630- 851- 5040
www.conwin.com
Application Note AN2093Page 4Revision P01Date 10 May 2013
2.9 Low-Dropout Regulators. Low-DropoutRegulators(LDOs)arelessefficientthandc-dcconverters,buttheyalsointroducesignificantlylessnoiseintothepowercircuits.
2.10 Power Supply Bulk Decoupling and Bypassing. Noisecanbeintroducedintothepowercircuitfromthevoltageregulator,fromICsconnectedtothenet,andfromelectromagneticnoisethatcouplesintothepowersupplytraceandplanes.Powersupply“bulk”decouplingcapacitorshelptominimizetheeffectsofnoiseandprovideotherbenefitstothecircuitaswell.Largevaluebulkcapacitorsimproveperformanceduringlowfrequencyfluctuationsinsupplycurrentdrawbyprovidingatemporarysourceofcharge.Manyvoltageregulatorsmaintaintheirvoltagebyusinganegativefeedbacklooptopologythatcanbecomeunstableatcertainfrequencies.Acapacitorplacedattheregulator’soutputcanpreventthevoltagesupplyfrombecomingunstable.Checktheregulator’smanufacturerdatasheetforrecommendedcapacitorspecifications.Bulkdecouplingcapacitorsshouldbeplacedascloseaspossibletotheoutputpinofthevoltageregulator.
2.11 Ground Circuits. Thegroundcircuitcanintroducenoisetoanembeddedsystemandaffectcomponents.Anidealgroundcircuitis“equipotential”,meaningthatthevoltageofthecircuitdoesnotchangeregardlessofthecurrent.Real-worldgroundcircuitshaveacharacteristicimpedanceandexperiencechangesinvoltagewithchangesincurrent.CarefulPCBdesigncanminimizethisnon-idealbehaviortocreateagroundcircuitthatprovidesalowimpedancereturnpathforcurrent.
2.12 Designing with a Ground Plane. WhilesomesystemsconnectcomponentstoagroundcircuitthroughwiresortracesmostdesignsuseagroundplaneinwhichthePCB’scomponentsconnecttheirgroundpinstoacommonconductiveplane.Designingwithagroundplaneishighlyrecommendedfortworeasons: • Thereturncurrentnoiseofonedevicehas lesseffectonothercomponentswhensharing groundinaparallelconfiguration. • Shortconnectionstogroundminimizecurrent returnpathinductance,whichcaninduce largevoltageswingsinground.
2.13 Ground Plane Fill. Agroundplaneshouldcoverasmuchoftheboardaspossible,eveninspacesbetweendevicesandtraces.
“Islands”ofcopperformedbetweentracesordevicesshouldalwaysbeconnectedtogroundandshouldneverbeleftfloating.Spreadingthegroundplaneacrosstheboardalsoaidsinnoisedissipationandshieldstraces.
Caution!CaremustbetakentothermallyisolatetheOCXOfromtheunderlyingpowerandgroundplanestoensuretheOCXOcanreachthermalequilibrium.Separatingtheanalogcurrentreturnpathfromthenoisierdigitalcurrentreturnpathcanimproveanalogmeasurements.Groundisolationcanalsoimproveperformanceinboardsconnectedtoindustrialornoisysystems.Separategroundplanesshouldbeconnectedinonlyonelocation,usuallynearthepowersupply.
“Caution!CaremustbetakentothermallyisolatetheOCXOfromtheunderlyingpowerandgroundplanestoensuretheOCXOcanreachthermalequilibrium.”
Section 2: Power & Ground Considerations continued
Application Note: AN2093 Page 5 of 20 Rev: P02 Date: 04/18/18© Copyright 2018 The Connor-Winfield Corp. All Rights Reserved Specifications subject to change without notice
All Rights Reserved. See website for latest revision. Not intended for life support applications.
2111 Comprehensive Drive
Aurora, Illinois 60505
Phone: 630-851-4722
Fax: 630- 851- 5040
www.conwin.com
Specifications subject to change without notice. All dimensions in inches. © Copyright 2012 The Connor-Winfield Corporation
Application Note AN2093Page 5Revision P01Date 10 May 2013
3.1 OCXO Theory of operation. TheOCXOenclosesacrystalinatemperature-controlledchambercalledanoven.Frequencystabilityisachievedbymaintainingtighttemperaturecontrolofthecrystalwithintheoscillatoroven.CaremustbetakennotwickthermalenergyawayfromtheOCXOpreventingthecorefromreachingthermalequilibrium. WhenanOCXOisturnedon,itgoesthrougha‘‘warm-up’’periodwhilethetemperatureofthecrystalintheinternalovenstabilizesatatemperaturesignificantlywarmerthanambient. During“warm-up”,theperformanceoftheoscillatorwillnotmeetthespecifiedfrequencystabilityuntilnormaloperatingtemperatureisreached.Aftertheovenhas“bridged”thetemperaturewithintheovenremainsconstantasambientvaries. Theovencontrolleroperatessuchthatiftheinternaltemperatureoftheovendecreasesduetoanambienttemperaturedrop,theovencontrollerwillprovidemorepowertocompensateforthermallosses.Similarly,anincreaseinambienttemperaturecausesareductioninappliedpowerintotheovenandthecompensationtemperaturedecreases. Inmostmoderndesignsadditionalheatisconsideredaproblemandwillcausemostdevicestodegradeinperformanceoreventuallyfail.TheheatgeneratedwithintheOCXOovencoreisusedtomaintainaconstanttemperatureatthecrystal.
“During“warm-up”,theperformanceoftheoscillatorisdegradeduntilnormaloperatingtemperatureisreached.”
Section 3: Theory of Operation / Characterization.
Figure: 5-01
ForfurtherinformationpleasecontactConnor-WinfieldEngineeringDepartment.
Application Note: AN2093 Page 6 of 20 Rev: P02 Date: 04/18/18© Copyright 2018 The Connor-Winfield Corp. All Rights Reserved Specifications subject to change without notice
All Rights Reserved. See website for latest revision. Not intended for life support applications.
Specifications subject to change without notice. All dimensions in inches. © Copyright 2012 The Connor-Winfield Corporation
Application Note AN2093Page 6Revision P01Date 10 May 2013
2111 Comprehensive Drive
Aurora, Illinois 60505
Phone: 630-851-4722
Fax: 630- 851- 5040
www.conwin.com
Typical Thermal Performance Characteristics.Test Conditions: OCXO mounted in socket, VCC=3.3V, Temperature = @25°C unless otherwise noted.
The following graphs represent the typical characteristics of a DOC052F-010.0MHz OCXO. Consult with Connor-Winfield Engineering Department for characterization data on any of our existing models.
Time (s)
Vol
tage
(V
)C
urre
nt (
A)
Figure: 6-01 Figure: 6-02
Figure: 6-03
Section 3: Theory of Operation / Characterization continued
Application Note: AN2093 Page 7 of 20 Rev: P02 Date: 04/18/18© Copyright 2018 The Connor-Winfield Corp. All Rights Reserved Specifications subject to change without notice
All Rights Reserved. See website for latest revision. Not intended for life support applications.
Specifications subject to change without notice. All dimensions in inches. © Copyright 2012 The Connor-Winfield Corporation
Application Note AN2093Page 7Revision P01Date 10 May 2013
2111 Comprehensive Drive
Aurora, Illinois 60505
Phone: 630-851-4722
Fax: 630- 851- 5040
www.conwin.com
Typical Thermal Performance Characteristics.
Figure: 7-01 Typical Warm-up Time (seconds) Figure: 7-02 Retrace after power cycle.
Figure: 7-03 Typical Warm-up Time (seconds) Figure: 7-04 Typical Warm-up Retrace Curves
Section 3: Theory of Operation / Characterization continued
Application Note: AN2093 Page 8 of 20 Rev: P02 Date: 04/18/18© Copyright 2018 The Connor-Winfield Corp. All Rights Reserved Specifications subject to change without notice
All Rights Reserved. See website for latest revision. Not intended for life support applications.
Specifications subject to change without notice. All dimensions in inches. © Copyright 2012 The Connor-Winfield Corporation
Application Note AN2093Page 8Revision P01Date 10 May 2013
2111 Comprehensive Drive
Aurora, Illinois 60505
Phone: 630-851-4722
Fax: 630- 851- 5040
www.conwin.com
Typical Thermal Performance Characteristics.
Figure: 8-01 Typical Warm-up Retrace Curves Figure: 8-02 Typical Oscillator Output Start Time
Figure: 8-03 Frequency Error vs Supply Voltage drift ( nom, +5,-5,nom)
Figure: 8-04 Typical Frequency Stability vs Temperature
Section 3: Theory of Operation / Characterization continued
Application Note: AN2093 Page 9 of 20 Rev: P02 Date: 04/18/18© Copyright 2018 The Connor-Winfield Corp. All Rights Reserved Specifications subject to change without notice
All Rights Reserved. See website for latest revision. Not intended for life support applications.
Specifications subject to change without notice. All dimensions in inches. © Copyright 2012 The Connor-Winfield Corporation
Application Note AN2093Page 9Revision P01Date 10 May 2013
2111 Comprehensive Drive
Aurora, Illinois 60505
Phone: 630-851-4722
Fax: 630- 851- 5040
www.conwin.com
Typical Thermal Performance Characteristics.Test Conditions: OCXO mounted on 0.062” 6 layer board, VCC=3.3V, Temperature = @25°C unless otherwise noted.
The following graphs represent the typical characteristics of a DOC052F-010.0MHz OCXO. Consult with Connor-Winfield Engineering Department for characterization data on any of our existing models.
Time (s)
Vol
tage
(V
)C
urre
nt (
A)
Figure: 9-01 Figure: 9-02
Figure: 9-03
Section 3: Theory of Operation / Characterization continued
Application Note: AN2093 Page 10 of 20 Rev: P02 Date: 04/18/18© Copyright 2018 The Connor-Winfield Corp. All Rights Reserved Specifications subject to change without notice
All Rights Reserved. See website for latest revision. Not intended for life support applications.
Specifications subject to change without notice. All dimensions in inches. © Copyright 2012 The Connor-Winfield Corporation
Application Note AN2093Page 10Revision P01Date 10 May 2013
2111 Comprehensive Drive
Aurora, Illinois 60505
Phone: 630-851-4722
Fax: 630- 851- 5040
www.conwin.com
Typical Thermal Performance Characteristics.
Figure: 10-01 Typical Warm-up Time (seconds) Figure: 10-02 Retrace after power cycle.
Figure: 10-03 Typical Warm-up Time (seconds) Figure: 10-04 Typical Warm-up Retrace Curves
Section 3: Theory of Operation / Characterization continued
Application Note: AN2093 Page 11 of 20 Rev: P02 Date: 04/18/18© Copyright 2018 The Connor-Winfield Corp. All Rights Reserved Specifications subject to change without notice
All Rights Reserved. See website for latest revision. Not intended for life support applications.
Specifications subject to change without notice. All dimensions in inches. © Copyright 2012 The Connor-Winfield Corporation
Application Note AN2093Page 11Revision P01Date 10 May 2013
2111 Comprehensive Drive
Aurora, Illinois 60505
Phone: 630-851-4722
Fax: 630- 851- 5040
www.conwin.com
Typical Thermal Performance Characteristics.
Figure: 11-01 Typical Warm-up Retrace Curves Figure: 11-02 Typical Oscillator Output Start Time
Figure: 11-03 Frequency Error vs Supply Voltage drift ( nom, +5,-5,nom)
Figure: 11-04 Typical Frequency Stability vs Temperature
Section 3: Theory of Operation / Characterization continued
Application Note: AN2093 Page 12 of 20 Rev: P02 Date: 04/18/18© Copyright 2018 The Connor-Winfield Corp. All Rights Reserved Specifications subject to change without notice
All Rights Reserved. See website for latest revision. Not intended for life support applications.
Specifications subject to change without notice. All dimensions in inches. © Copyright 2012 The Connor-Winfield Corporation
Application Note AN2093Page 12Revision P01Date 10 May 2013
2111 Comprehensive Drive
Aurora, Illinois 60505
Phone: 630-851-4722
Fax: 630- 851- 5040
www.conwin.com
Typical Electrical CharacteristicsTest Conditions: OCXO mounted on 0.062” 6 layer board, VCC=3.3V, Temperature = @25°C unless otherwise noted.
The following graphs represent the typical characteristics of a DOC052F-010.0MHz OCXO. Consult with Connor-Winfield Engineering Department for characterization data on any of our existing models.
Figure: 12-01 Typical Oscillator Output Start Time Figure: 12-02 Control Voltage Tuning Linearity
Figure: 12-03 Typical Phase Noise Plot Figure: 12-04 Available Tuning Slopes
Section 3: Theory of Operation / Characterization continued
Application Note: AN2093 Page 13 of 20 Rev: P02 Date: 04/18/18© Copyright 2018 The Connor-Winfield Corp. All Rights Reserved Specifications subject to change without notice
All Rights Reserved. See website for latest revision. Not intended for life support applications.
Specifications subject to change without notice. All dimensions in inches. © Copyright 2012 The Connor-Winfield Corporation
Application Note AN2093Page 13Revision P01Date 10 May 2013
2111 Comprehensive Drive
Aurora, Illinois 60505
Phone: 630-851-4722
Fax: 630- 851- 5040
www.conwin.com
Typical Electrical Characteristics
Figure: 13-01 Figure: 13-02
Figure: 13-03 Figure: 13-04
Fre
que
ncy
Err
or
(pp
b)
Section 3: Theory of Operation / Characterization continued
Application Note: AN2093 Page 14 of 20 Rev: P02 Date: 04/18/18© Copyright 2018 The Connor-Winfield Corp. All Rights Reserved Specifications subject to change without notice
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See FIGURE 13-01.
Specifications subject to change without notice. All dimensions in inches. © Copyright 2012 The Connor-Winfield Corporation
Application Note AN2093Page 14Revision P01Date 10 May 2013
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Phone: 630-851-4722
Fax: 630- 851- 5040
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4.1 Layout Considerations ToachievethestatedfrequencystabilityspecificationstheOCXOmustbeabletoreachandsustainthermalequilibriumoverALLoperatingconditions.Observationoftheambientoperatingtemperaturerange,controlledairflow,thermalrampratesandminimizingthermalenergygains/lossesarecriticalforasuccessfullayout. “Anyattempttocool,ordispersethisheatwillcauseovencoretemperaturetodriftandOCXOwillnotmeetthespecifiedfrequencystability.Improperboardlayoutcouldalsoallowheattransferfromnearbycomponentstooverheattheovencoreresultinginlossofspecifiedfrequencystability.” Severalthermaldesignparametersmustbecarefullyconsidered. • BoardLayoutConsiderations • ControllingThermalTransfer/Transients • ControllingAirFlow
4.2 Board Layout Considerations Carefulselectionoflayerstack-ups,groundfills,andtraceroutingishighlyrecommendedforasuccessfullayout. “ToachievethestatedfrequencystabilitytheOCXOmustbeabletoreachandsustainthermalequilibriumoverALLoperatingconditions” Considerthefollowinglayoutconcerns. 1. AlwaysplacetheOCXOnearthetimingcircuitry, andkeepallPower/GroundandRFtracesas smallaspossible. 2. Alwaysadheretostatedloadingspecifications} forOCXORFoutput.OCXOsareloadsensitive andrequireanequivalentloadcapacitorwitha flatcapacitancevs.temperaturecurveto achievestatedfrequencystabilityspecifications. ConsiderNPO/COGcapacitorswhenpractical foroptimaltemperaturecharacteristics.See FIGURE13-01FrequencyResponsetovarious equivalentcapacitiveloads. 3. UsesecondarybufferstofantheOCXORF signaltomultipleinputsortimingcircuits.Avoid designsthatwould“switchin”additional capacitiveloads.Avoiddesignsthatwould “switchbetween”multiplecapacitiveloads. OCXOsareloadsensitivedevices. SeeFIGUREXXX
Section 4: Multi-Layer Board Design / Thermal Considerations
4. Alwaysusespeedratedleveltranslatorsor buffersinapplicationsrequiringcommunication betweendigitaldevicesoperatingfrommultiple supplyvoltages.Neveruseresistordivider networksonRFsignals. 5. Itisrecommendedtoplacea10uFto47uFbulk capacitorasclosetoaspossibletotheVCCpin ofthedevice. 6. Placeasmallceramicdecouplingcapacitor typicallyNPO/COG/X7Rwitha2to3ohm reactanceattheoutputfrequencyofthe OCXOtoshuntanynoiseonthesupplyrailto ground.Additionaldecouplingcapacitors canbeusedtofilteroutotherunwantedsupply noisegeneratedfromotherdevices. 7. Avoidusingseriescurrentsenseresistorsin OCXOmonitoringapplications.Improper selectionofresistorvaluescouldcreate significantvoltagedropswhencombinedwith thethermalcoefficientsofthesupply,andlarge currentdrawfromtheOCXO. 8. Carefulevaluationofviasizeshouldbe consideredwithallhighpowerdevicesto guaranteesufficientcurrent.Maximum currentthroughaviacalculationsshouldbe madeusinghighestexpectedboardtemperature insteadofmaximumambienttemperatureas heatgeneratingcomponentswilltypicallyheat theboardwellbeyondtheambienttemperature rangeoftheOCXO.Improperviasizeselection couldcausecurrentstarvationissueswhich wouldresultincurrentoscillationsastheoven coreisstarvedofpowerandunabletoreach thermalequilibrium.Viatopadstringers orrunnersshouldalsobeevaluatedforsufficient currentcarryingcapacityatmaximumexpected boardtemperatures.Viainpadworkbest,but addsadditionalboardcost.
Application Note: AN2093 Page 15 of 20 Rev: P02 Date: 04/18/18© Copyright 2018 The Connor-Winfield Corp. All Rights Reserved Specifications subject to change without notice
All Rights Reserved. See website for latest revision. Not intended for life support applications.
Specifications subject to change without notice. All dimensions in inches. © Copyright 2012 The Connor-Winfield Corporation
Application Note AN2093Page 15Revision P01Date 10 May 2013
2111 Comprehensive Drive
Aurora, Illinois 60505
Phone: 630-851-4722
Fax: 630- 851- 5040
www.conwin.com
Multi-Layer Board Design / Thermal Considerations
9. Lowimpedancepowerandgroundplanes shouldbeusedinsteadofstringertracesorstar basedpowerdistributionmethodstoreduce inducedvoltagescausedbyhighcurrent devicessuchasOCXOs. 10. Forcontrolvoltageequippedmodelsitis importanttoconnectthegroundofthecontrol voltagesourceascloseaspossibletotheOCXO groundtominimizetraceimpedanceand thereforeminimizeanygeneratedvoltages whichcouldcauselargefrequencyerrors.Itis highlyrecommendedtousethesupplied OCXOVREFsourcetoderivethecontrolvoltage whenequipped.Formodelsthatdonotoffer theOCXOVREFsourceitisalsorecommended thatthecontrolvoltagesourcerunoffthesame railastheOCXOtoeliminatethesupplyvoltage thermaldrifterrorsthatcouldexistbetween multiplerails.Thiswillpreventlargeunwanted frequencyshifterrorsastherelativevoltagedrift betweenthesupplieswillbeeliminated. Scenario:Assumeacontrolvoltageequipped OCXOwithatuningsensitivityof7ppm/voltis poweredfroma3.3Vsupply(3V3_OCXOSupply) withatemperaturecoefficientof2.6mV/°C.
Freeviasizecalculationstoolsareavailableonline.SaturnPCBDesignInc.offersthisfreetoolavailableatthefollowingURL.
Figure: 15-01
TheDACwhichdrivestheOCXOCVpinis poweredfromasecondary3.3Vrail(3v3_ DacSupply)withathermalcoefficientof 0.2mV/°C(SeeFigure15-02Example schematicFigure15-03ThermalCoefficientvs. Temperature)InthisexampletheOCXOwas initiallytunedto0ppmat0°Cwithacalibration errorof±0.025ppm.Astheambient temperatureinthesystemchangesto70°Cover thenexthour,thevoltageerrorbetweenthetwo railswouldhavedriftedfrom0voltsbetween thetworails,to0.1834voltsresultingina 1.2838ppmfrequencyerror.
DNC
DNC
Figure: 15-03 Thermal Drift between Supply Rails
Figure: 15-02 Example Circuit
http://saturnpcb.com/pcb_toolkit.htm
Section 4: Multi-Layer Board Design / Thermal Considerations continued
Application Note: AN2093 Page 16 of 20 Rev: P02 Date: 04/18/18© Copyright 2018 The Connor-Winfield Corp. All Rights Reserved Specifications subject to change without notice
All Rights Reserved. See website for latest revision. Not intended for life support applications.
Specifications subject to change without notice. All dimensions in inches. © Copyright 2012 The Connor-Winfield Corporation
Application Note AN2093Page 16Revision P01Date 10 May 2013
2111 Comprehensive Drive
Aurora, Illinois 60505
Phone: 630-851-4722
Fax: 630- 851- 5040
www.conwin.com
Multi-Layer Board Design / Thermal Considerations
Figure: 16-01AsmallairgapshouldexistbetweentheOCXOandallthe
wallsofthecover.
Figure: 16-02OCXOPadLayoutw/TopLevelCopperpour.
11. Toreduceunwantedthermalgains/losses, openawindowinanytoplevelcopperpours underthedevice.Excessivethermallosses mayresultinhigherthannormalcurrent consumptionorcompletedevicefailure.See Figure16-03.Excessivethermalgainswill overheattheovencorecausingfrequency instability.FIGURE16-02illustratesahowto properlyfloodatoplayerwhilecreatinga “window”undertheOCXO.
Figure: 16-03
12. Optionallyathermal“moat”canbecreatedto preventthermalenergytransfersbetweenthe OCXOandboardasseeninFigure17-01.A thermalmoatisaroutedareaaroundtheOCXO andisveryeffectivemeanstopreventlosses fromtheoscillatorwhilestillallowingatoplayer pourontheboardtoheatsinkcoolother electricalcomponents. 13. Plasticandmetalcoverscanbeusedtofurther reducesmalltemperaturefluctuationsinthe systembyreducingvariableairflowacrossthe device.Aneffectivecoverwillshouldstillallow asmallairgapbetweentheOCXOandanywall ofthecover.SEEFIGURE16-01 14. DONOTCONNECTANYELECTRICALSIGNALS TOPINSMARKEDDNC.Thesepinsare reservedforfactoryuseonly,andconnectingor monitoringthesesignalscouldpermanently damagethedevice.
Section 4: Multi-Layer Board Design / Thermal Considerations continued
Application Note: AN2093 Page 17 of 20 Rev: P02 Date: 04/18/18© Copyright 2018 The Connor-Winfield Corp. All Rights Reserved Specifications subject to change without notice
All Rights Reserved. See website for latest revision. Not intended for life support applications.
Specifications subject to change without notice. All dimensions in inches. © Copyright 2012 The Connor-Winfield Corporation
Application Note AN2093Page 17Revision P01Date 10 May 2013
2111 Comprehensive Drive
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Phone: 630-851-4722
Fax: 630- 851- 5040
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Multi-Layer Board Design / Thermal Considerations
Figure: 17-01
Optionallyathermal“moat”canbecreatedtopreventthermalenergytransfersbetweentheOCXOandthesurroundingheatgeneratingcomponents.
Section 4: Multi-Layer Board Design / Thermal Considerations continued
Application Note: AN2093 Page 18 of 20 Rev: P02 Date: 04/18/18© Copyright 2018 The Connor-Winfield Corp. All Rights Reserved Specifications subject to change without notice
All Rights Reserved. See website for latest revision. Not intended for life support applications.
Specifications subject to change without notice. All dimensions in inches. © Copyright 2012 The Connor-Winfield Corporation
Application Note AN2093Page 18Revision P01Date 10 May 2013
2111 Comprehensive Drive
Aurora, Illinois 60505
Phone: 630-851-4722
Fax: 630- 851- 5040
www.conwin.com
Multi-Layer Board Design / Thermal Considerations
4.3 Controlling Thermal Transfer / Transients ControllingthermaltransientsiscriticalforproperoperationofallOCXOs.Anysuddenchangesinair-flow,ortemperaturewilldrasticallyeffectshorttermfrequencystability.Ambientsystem,cabinet,orenclosuretemperaturemustalwaystransitionunderthemaximumstatedrateidentifiedontheproductdatasheet.Typical∆tºC/t(minutes)ratesforOCXOrangefrom0.5to1ºC/minute.Anyadditionalheatgeneratedbynearbyintegratedcircuits,ormechanicalpartscouldcausetheinternaloventemperaturetofalloutofequilibriumandnolongermaintainfrequencystability.TheOCXOcontrollercanonlyself-regulateovencoretemperatureifthermalenergyconductedthroughtheprintedcircuitboardiskepttoaminimum.
Avoidthefollowing,astheywillcausetheovencoretooverheatordropoutofthermalregulation.
• PlacingtheOCXOnearheatgenerating components(electricalormechanicalthatcould bleedthermalenergyintotheOCXOcausing theovencoretooverheat,evenwhenthe ambientairiswithintheoperatinglimits)
• PlacingtheOCXOintointermittentairflowpaths (ieswitchedorvariablespeedfans)asthiswill causetheovencoretofalloutofthermal regulation
• Onmulti-layerboardsavoidtoplevelcopper floods,poursandfillsundertheOCXOland patternthatwouldcontributetoexcessiveheat gains/lossesthroughtheprintedcircuitboard resultinginaninabilityfortheovencoreto maintainthermalequilibrium.
AvoidlayoutsasseeninFIGURE18-02
4.4 Controlling AirflowShieldingtheOCXOfromintermittentorvariablespeedairflowpathswillminimizesmalltemperaturefluctuationsandsubstantiallyimproveshort/mediumtermstability.ThiscanbestbeaccomplishedbyshieldingtheOCXObehindtallernon-heatgeneratingcomponentsormechanicalpartstocreateaphysicalbarrier,orwiththeuseofametalorplasticcover.
Seefigures18-01and18-02
Figure: 18-01GoodChoiceforOCXOplacement.OCXOisoutsideofairtunnel,notnearanyheatgeneratingcomponents
Figure: 18-02PoorlocationforOCXO.Variablespeedorswitchedfanscreatelargetemperaturefluctuations
Section 4: Multi-Layer Board Design / Thermal Considerations continued
Application Note: AN2093 Page 19 of 20 Rev: P02 Date: 04/18/18© Copyright 2018 The Connor-Winfield Corp. All Rights Reserved Specifications subject to change without notice
All Rights Reserved. See website for latest revision. Not intended for life support applications.
Specifications subject to change without notice. All dimensions in inches. © Copyright 2012 The Connor-Winfield Corporation
Application Note AN2093Page 19Revision P01Date 10 May 2013
2111 Comprehensive Drive
Aurora, Illinois 60505
Phone: 630-851-4722
Fax: 630- 851- 5040
www.conwin.com
Section 5: Design Checklist
5.1 Power Supply Checklist • SelectaLOWnoisepowercircuit/source • Addalargebulkcapacitoratthevoltageregulator’soutputthatcanprovidecurrentforlocalcapacitorsand ensureregulatorstability. • Placebulkcapacitorsasclosetothevoltageregulatoroutputaspossible. • Thelargebulkcapacitor’scapacitanceshouldbe10to100timesaslargeaslocalICdecouplingcapacitors. • Addasecondcapacitoranorderofmagnitudeortwosmallerincapacitancerelativetothelargebulk capacitortohelpfilterhigh-frequencynoise. • PlacealocalcapacitanceascloseaspossibletothepowersupplypinofeachIC. • ThesideofthelocalcapacitorthatconnectstogroundshouldbeplacedasclosetotheIC’sgroundpinas possibleinordertominimizetheloopareabetweenthecapandthepowerandgroundpins. • Addafilter,suchasanL-CfilteroranR-Cfilter,tothepowersupplycircuit.
5.2 Ground
• Designusingagroundplaneinsteadoftraceswhenconnectingcomponentstoground. • Ifatoplevelcopperpourisused,itshouldcoverasmuchoftheboardaspossible,includingthespaces betweendevicesandtraces.EXCLUDETHEAREAUNDERTHEOCXO. • Separatingtheanaloggroundplanefromthedigitalgroundplaneimprovesanalogperformance. • Separategroundplanesshouldbeconnectedinonlyonelocation,usuallyclosetothepowersupply.
5.3 General • Keepanaloganddigitalsignalsasfarapartfromeachotheraspossible. • Avoidroutinganaloganddigitaltracesperpendiculartoeachother. • Avoidroutinganalogordigitalsignalsunderoscillators. • Tracewidthshouldremainconstantthroughoutthelengthofthetrace. • Turnsintracesshouldberoutedusingtwo45degreeturnsinsteadofone90degreeturn. • Tracelengthshouldalwaysbeminimized. • Useviasonlywhenabsolutelynecessary. • Avoidtheuseofviaswhenroutinghigh-frequencysignals. • Keeptracesassmallaspossible. • PlacetheOCXOascloseaspossibletothetimingcircuitry. • Neverleavethecontrolvoltagesignalfloating. • Designusingapowerplaneinsteadoftracesroutedfromthepowersupply.
Application Note: AN2093 Page 20 of 20 Rev: P02 Date: 04/18/18© Copyright 2018 The Connor-Winfield Corp. All Rights Reserved Specifications subject to change without notice
All Rights Reserved. See website for latest revision. Not intended for life support applications.
Specifications subject to change without notice. All dimensions in inches. © Copyright 2012 The Connor-Winfield Corporation
Application Note AN2093Page 20Revision P01Date 10 May 2013
2111 Comprehensive Drive
Aurora, Illinois 60505
Phone: 630-851-4722
Fax: 630- 851- 5040
www.conwin.com
Design Checklist
5.4 OCXO Layout Considerations • AlwaysplaceOCXOasclosetotimingcircuitryaspossible.. • AlwaysadheretostatedloadingspecificationsforRFoutputofOCXOandconsiderusingNPO/COG capacitorstocreateequivalentloadingcapacitanceforoptimalcapacitancevs.temperaturecharacteristics. • Itisrecommendedtoplacea10uFto47uFbulkcapacitorasclosetoaspossibletotheVCCpinoftheOCXO. • PlaceasmallceramicdecouplingcapacitortypicallyX7Rwitha2to3ohmreactanceattheoutputfrequency oftheOCXOtoshuntanynoiseonthesupplyrailtoground. • CalculateviasizetoensuresufficientcurrentisavailabletotheOCXOattheanticipatedmaximumboard temperaturewhichmaybeSIGNIFICANTLYhigherthanambientairtemperature. • ConnectthegroundofthecontrolvoltagesourceascloseaspossibletotheOCXOgroundtominimizetrace impedance. • Openawindowinallgroundandpowerplanesunderthedevice.Excessivethermallossesmayresultin higherthannormalcurrentconsumptionorcompletedevicefailure. • DonotplaceOCXOinpathorturbulentairflowwhichcouldcausequicklychangingtemperaturefluctuations thatcouldcompromisetheovencoretemperature. • [Optional]Routeathermal“moat”topreventthermalenergytransfersbetweentheOCXOandboard. • [Optional]Useplasticandmetalcoverscanbeusedtofurtherreducesmalltemperaturefluctuationsinthe systembyreducingvariableairflowacrossthedevice. • DONOTconnectanysignalsto“DoNotConnect”(D.N.C.)pins.TheseareFACTORYuseonly.DNCpads maybesoldereddowntoelectricallyisolatedpadsforstructuralsupportonly.
Section 6: References
ChesterSimpson"LinearandSwitchingVoltageRegulatorFundamentals"NationalSemiconductorhttp://www.national.com/assets/en/appnotes/f4.pdf
HabeebUrRahmanMohammed,Ph.D"SupplyNoiseEffectonOscillatorPhaseNoise,"TexasInstruments,ApplicationReportSLWA066–November2011http://www.ti.com/lit/an/slwa066/slwa066.pdf
Section 5: Design Checklist continued