Five Steps to a Good PCB Layout of the Boost …

1 1 SLVA773 May 2016 SubmitDocumentationFeedbackCopyright 2016,TexasInstrumentsIncorporatedFive Stepsto a GoodPCBL ayoutof a BoostConverterUser's GuideSLVA773 May 2016 FiveStepstoa GoodPCBL ayoutofa BoostConverterA goodPCBlayoutis criticalfor the reasonis that the boostconverteris sensitivetoparasiticcapacitanceand inductancebecauseof the bad PCBlayoutwouldintroducelargeparasiticcap acitanceand inductance,whichwouldcausehighoutputripp le,pooroutputvoltageregulationand currentlimit accuracy,electromagneticinterference(EMI )problem,and evenfailureby the helpto avoidmostof theseproblemsof the boostconverterwithoutextracost if thoughtis spentbeforethe first PCBis layoutof the boostconverterfromits datasheetor evaluationmodule(EVM)

2 Is easiest,butthe layoutmay not fit the this applicationnotedetailsfive stepsthat help to designagoodPCBlayoutfor the high-currentboostconverter,TPS61236as showninFigure1 is takenas the exampleto demonstratethe five May 2016 SubmitDocumentationFeedbackCopyright 2016,TexasInstrumentsIncorporatedFive Stepsto a GoodPCBL ayoutof a Routethe OutputCapacitorThe outputcapacitorlocationis the mostimportantfor any boostconverter,so it shouldbe placedcloseto the IC. Routethe capacitorto the IC with shortand widetraceto minimizethe reasonis that the currentflowingthroughthe outputcapacitorsis pulse-type[1].

3 Consideringthe V = L dI / dt, the parasiticinductancebetweenthe IC and the outputcapacitorswouldcausevoltagespikean d ringingat the SW pin. Too high voltagespikecan damagethe IC andthe ringingcausesEMI showshow to placeand routethe outputcapacitorsfor the the left, the three0805packagecapacitorsare placedin way is easyand has very sometimes,it is not easyto placethe largepackagecapacitorscloseto the ICbecauseof the restrictionof the smallpackagecapacitorcan be placedneartheIC and the bulk capacitorsare bulk capacitorcan be connectedwiththe IC throughrelativelong traceand vias.

4 As shownin the rightof is suggestedto use one via per ampof currentif the via is required[2]. Morevias help to reduceparasiticresistanceif bothcases,makesurethe tracesbetweenthe IC and outputcapacitorare wideenoughto supportthe Placeand Routethe Routethe Inductorand SnubberThe secondcomponentto be placedis the reducethe radiatedEMI,the inductorshouldbe placedcloseto the IC. The copperof the SW-nodeshouldbe optimizedto handlethe largecurrentwith SW-nodeis the noisysourceof the boostconverter,so any traceof asensitivenode,suchas FB, shouldbe far awayfromthe SW showsthe placementandroutingof the inductorin the two Placeand Routethe May 2016 SubmitDocumentationFeedbackCopyright 2016.

5 TexasInstrumentsIncorporatedFive Stepsto a GoodPCBL ayoutof a BoostConverterSnubbercircuitin the SW-nodeis unnecessaryfor the normaloperationof a it isoccasionallyrequiredto reducethe EMI by dampingthe ringingand slowingdownthe voltagerisingand fallingedgeat the be effective,the loop areaof the snubbercircuit(Rs and Cs)shouldbe as smallas possibleto minimizethe parasiticinductance,as shownin Placeand Routeof the May 2016 SubmitDocumentationFeedbackCopyright 2016,TexasInstrumentsIncorporatedFive Stepsto a GoodPCBL ayoutof a Routethe InputCapacitorand VIN PinThe inputcapacitoris the final powercomponentto be inputcapacitoris also usedtopowerthe internalcontrolcircuitand the inputvoltagedetectioncircuitfor undervoltagelockout(UVLO).

6 So the ground-nodeof the inputcapacitorshouldbe closeto the IC powergroundpin. Theinputcapacitorground-node,outputcapac itorground-nodeand the IC ground-pinforma Power-Groundof the distancebetweenVIN-nodeof the inputcapacitorand inductorisnot importantbecausethe currentthroughthe inputcapacitoris VIN voltageis usuallystablevoltage,so a largeVIN-nodecopperareawouldnot causetroubleand a largecopperareacan help to improvethe showsthe placementof the inputcapacitorwithoutand with a snubbercircuitis moreimportantthaninputcapacitor,so it shouldbe placedfirst.

7 If the snubbercircuitis unnecessaryfor mostof the applicationconditions,it will be not includedin the VIN pin of the IC can be connectedwith the VIN-nodeof the inputcapacitorthroughvias anddirecttracein anotherlayerbecausethe currentthroughthis traceis this traceis too long,asmalldecouplingcapacitorcan be placedclosedto the VIN pin of the Placeand Routethe InputCapacitorand VIN May 2016 SubmitDocumentationFeedbackCopyright 2016,TexasInstrumentsIncorporatedFive Stepsto a GoodPCBL ayoutof a Routethe SmallSignalComponentsThe smallsignalcomponentsincludeboththe analogand the TPS61236boostconverter,the smallsignalanalogcomponentsare the resistorsand capacitors(R1, R2, R5, C5) forthe CC and FB pin.

8 The smallsignallogiccomponentsare the resistors(R3, R4) for INACTand analogcomponentsand nodesare sensitiveto noise,especiallywhenthey havelargeinputimpedance,suchas FB pin. Makesurethesecomponentsare closeto the IC. The tracesbetweenthecomponentsand IC shouldbe shortto minimizethe parasiticcapacitancewith noisySW FB tracein parallelwith the SW nodeclosely;otherwisethe switchingnoisewouldcoupletothe FB pin and showsthe layoutof the Placeand Routeof AnalogSmallSignalComponentsThe logiccircuitfor EN and INACT pins is less circuitsnormallyhaverelativelysmallimped anceand smallvoltagenoiseat thesepins doesnot placedand routedlast.

9 As shownin Figure7, the resistorsare connectedwith the ICpins throughvias and tracein Placeand Routethe May 2016 SubmitDocumentationFeedbackCopyright 2016,TexasInstrumentsIncorporatedFive Stepsto a GoodPCBL ayoutof a SignalGroundand PlacePolygonPlaneThe ground-nodeof the analogsmallsignalcomponentsand AGNDpin of the IC forma Signal-Ground,whichmustbe connectedto the Power-Groundof the IC througha singlepointshouldbe closedto the PGNDpin. Makesureno largepowercurrentis ,noisecouplinginto the controlcircuitcouldcausesbad outputvoltageregulation,inaccuratecurren tlimit,or showsa goodexampleofSignal-Groundand Routethe SignalGroundThe ground-nodesof the logiccircuitsare normallyconnectedto the Signal-Groundas in Figure8.

10 Butthey can also be connectedto Power-Groundif they are too far awayfromthe voltagenoisecouplinginto the logiccircuitis not too high to interferethe IC mainlydissipatesheatthroughthe VOUTand GNDpin. The largecopperplanein thesepinshelpsto recommendsincreasingthe copperareaas largeas possiblein the GNDlayeras shownin Figure9. Thickcopper,vias betweenthe top layerand the bottomlayer,and thin dielectriclayeralso help to improvethe Placethe GroundPolygonPlaneThe Signal-Groundcan be connectedto the groundplanedirectlywithoutlargepowercurr entflowingthroughthe Signal-Ground,as shownin Figure10.