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11PowerSupplyRecommendations
11.1TUSB8041PowerSupply
VDDshouldbeimplementedasasinglepowerplane,asshouldVDD33.
?TheVDDpinsoftheTUSB8041supply1.1V(nominal)powertothecoreoftheTUSB8041.Thispowerrailcanbeisolatedfromallotherpowerrailsbyaferritebeadtoreducenoise.
?TheDCresistanceoftheferritebeadonthecorepowerrailcanaffectthevoltageprovidedtothedeviceduetothehighcurrentdrawonthepowerrail.TheoutputofthecorevoltageregulatormayneedtobeadjustedtoaccountforthisoraferritebeadwithlowDCresistance(lessthan0.05Ω)canbeselected.
?TheVDD33pinsoftheTUSB8041supply3.3VpowerrailtotheI/OoftheTUSB8041.Thispowerrailcanbeisolatedfromallotherpowerrailsbyaferritebeadtoreducenoise.
?Allpowerrailsrequirea10μFcapacitoror1μFcapacitorsforstabilityandnoiseimmunity.Thesebulkcapacitorscanbeplacedanywhereonthepowerrail.ThesmallerdecouplingcapacitorsshouldbeplacedasclosetotheTUSB8041powerpinsaspossiblewithanoptimalgroupingoftwoofdifferingvaluesperpin.
11.2DownstreamPortPower
???
Thedownstreamportpower,VBUS,mustbesuppliedbyasourcecapableofsupplying5Vandupto900mAperport.DownstreamportpowerswitchescanbecontrolledbytheTUSB8041signals.Itisalsopossibletoleavethedownstreamportpoweralwaysenabled.
Alargebulklow-ESRcapacitorof22μForlargerisrequiredoneachdownstreamport’sVBUStolimitin-rushcurrent.
TheferritebeadsontheVBUSpinsofthedownstreamUSBportconnectionsarerecommendedforbothESDandEMIreasons.A0.1μFcapacitorontheUSBconnectorsideoftheferriteprovidesalowimpedancepathtogroundforfastrisetimeESDcurrentthatmighthavecoupledontotheVBUStracefromthecable.
11.3Ground
Itisrecommendedthatonlyoneboardgroundplanebeusedinthedesign.Thisprovidesthebestimageplaneforsignaltracesrunningabovetheplane.ThethermalpadoftheTUSB8041andanyofthevoltageregulatorsshouldbeconnectedtothisplanewithvias.AnearthorchassisgroundisimplementedonlyneartheUSBportconnectorsonadifferentplaneforEMIandESDpurposes.
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12Layout
12.1LayoutGuidelines
12.1.1Placement
1.9.53K+/-1%resistorconnectedtopinUSB_R1shouldbeplacedascloseaspossibletotheTUSB8041.2.A0.1μFshouldbeplacedascloseaspossibleoneachVDDandVDD33powerpin.
3.The100nFcapacitorsontheSSTXPandSSTXMnetsshouldbeplacedclosetotheUSBconnector(TypeA,TypeB,andsoforth).
4.TheESDandEMIprotectiondevices(ifused)shouldalsobeplacedaspossibletotheUSBconnector.5.Ifacrystalisused,itmustbeplacedascloseaspossibletotheTUSB8041’sXIandXOpins.
6.PlacevoltageregulatorsasfarawayaspossiblefromtheTUSB8041,thecrystal,andthedifferentialpairs.7.Ingeneral,thelargebulkcapacitorsassociatedwitheachpowerrailshouldbeplacedascloseaspossibletothevoltageregulators.12.1.2PackageSpecific
1.TheTUSB8041packagehasa0.5-mmpinpitch.
2.TheTUSB8041packagehasa6.0-mmx6.0-mmthermalpad.Thisthermalpadmustbeconnectedtogroundthroughasystemofvias.
3.Allviasunderdevice,exceptforthoseconnectedtothermalpad,shouldbesoldermaskedtoavoidanypotentialissueswiththermalpadlayouts.12.1.3DifferentialPairs
ThissectiondescribesthelayoutrecommendationsforalltheTUSB8041differentialpairs:USB_DP_XX,USB_DM_XX,USB_SSTXP_XX,USB_SSTXM_XX,USB_SSRXP_XX,andUSB_SSRXM_XX.1.Mustbedesignedwithadifferentialimpedanceof90Ω+/-10%.
2.Inordertominimizecrosstalk,itisrecommendedtokeephighspeedsignalsawayfromeachother.Eachpairshouldbeseparatedbyatleast5timesthesignaltracewidth.Separatingwithgroundasdepictedinthelayoutexamplewillalsohelpminimizecrosstalk.
3.Routealldifferentialpairsonthesamelayeradjacenttoasolidgroundplane.4.Donotroutedifferentialpairsoveranyplanesplit.
5.Addingtestpointswillcauseimpedancediscontinuityandwillthereforenegativeimpactsignalperformance.Iftestpointsareused,theyshouldbeplacedinseriesandsymmetrically.Theymustnotbeplacedinamannerthatcausesstubonthedifferentialpair.
6.Avoid90degreeturnsintrace.Theuseofbendsindifferentialtracesshouldbekepttoaminimum.Whenbendsareused,thenumberofleftandrightbendsshouldbeasequalaspossibleandtheangleofthebendshouldbe≥135degrees.ThiswillminimizeanylengthmismatchcausesbythebendsandthereforeminimizetheimpactbendshaveonEMI.
7.Minimizethetracelengthsofthedifferentialpairtraces.ThemaximumrecommendedtracelengthforSSdifferentialpairsignalsandUSB2.0differentialpairsignalsiseightinches.Longertracelengthsrequireverycarefulroutingtoassurepropersignalintegrity.
8.Matchtheetchlengthsofthedifferentialpairtraces(i.e.DPandDMorSSRXPandSSRXMorSSTXPandSSTXM).Thereshouldbelessthan5milsdifferencebetweenaSSdifferentialpairsignalanditscomplement.TheUSB2.0differentialpairsshouldnotexceed50milsrelativetracelengthdifference.
9.Theetchlengthsofthedifferentialpairgroupsdonotneedtomatch(i.e.thelengthoftheSSRXpairtothatoftheSSTXpair),butalltracelengthsshouldbeminimized.
10.Minimizetheuseofviasinthedifferentialpairpathsasmuchaspossible.Ifthisisnotpractical,makesurethatthesameviatypeandplacementareusedforbothsignalsinapair.AnyviasusedshouldbeplacedascloseaspossibletotheTUSB8041device.
11.Toeaserouting,thepolarityoftheSSdifferentialpairscanbeswapped.ThismeansthatSSTXPcanberoutedtoSSTXMorSSRXMcanberoutedtoSSRXP.
12.ToeaseroutingoftheUSB2DPandDMpair,thepolarityofthesepinscanbeswapped.Ifthisisdone,the
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LayoutGuidelines(continued)
appropriatePx_usb2polregister,wherex=0,1,2,3,or4,mustbeset.13.Donotplacepowerfusesacrossthedifferentialpairtraces.
12.2LayoutExamples
12.2.1UpstreamPort
Figure23.ExampleRoutingofUpstreamPort
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LayoutExamples(continued)
12.2.2DownstreamPort
Figure24.ExampleRoutingofDownstreamPort
Theremainingthreedownstreamportsroutingcanbesimilartotheexampleprovided.
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13DeviceandDocumentationSupport
13.1CommunityResources
ThefollowinglinksconnecttoTIcommunityresources.Linkedcontentsareprovided\IS\bytherespectivecontributors.TheydonotconstituteTIspecificationsanddonotnecessarilyreflectTI'sviews;seeTI'sTermsofUse.
TIE2E?OnlineCommunityTI'sEngineer-to-Engineer(E2E)Community.Createdtofostercollaboration
amongengineers.Ate2e.ti.com,youcanaskquestions,shareknowledge,exploreideasandhelpsolveproblemswithfellowengineers.DesignSupportTI'sDesignSupportQuicklyfindhelpfulE2Eforumsalongwithdesignsupporttoolsand
contactinformationfortechnicalsupport.
13.2Trademarks
E2EisatrademarkofTexasInstruments.
Allothertrademarksarethepropertyoftheirrespectiveowners.
13.3ElectrostaticDischargeCaution
Thesedeviceshavelimitedbuilt-inESDprotection.TheleadsshouldbeshortedtogetherorthedeviceplacedinconductivefoamduringstorageorhandlingtopreventelectrostaticdamagetotheMOSgates.
13.4Glossary
SLYZ022—TIGlossary.
Thisglossarylistsandexplainsterms,acronyms,anddefinitions.
14Mechanical,Packaging,andOrderableInformation
Thefollowingpagesincludemechanicalpackagingandorderableinformation.Thisinformationisthemostcurrentdataavailableforthedesignateddevices.Thisdataissubjecttochangewithoutnoticeandrevisionofthisdocument.Forbrowser-basedversionsofthisdatasheet,refertotheleft-handnavigation.
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