A Series
1 5 - 1 7 W , D U A L O U T P U T D C / D C C O N V E R T E R S
Externalꢀinputꢀcapacitorsꢀ(CINꢀinꢀFigureꢀ2)ꢀserveꢀprimarilyꢀasꢀenergy-storageꢀ
elements,ꢀminimizingꢀlineꢀvoltageꢀvariationsꢀcausedꢀbyꢀtransientꢀIRꢀdropsꢀinꢀ
conductorsꢀfromꢀbackplaneꢀtoꢀtheꢀDC/DC0ꢀInputꢀcapsꢀshouldꢀbeꢀselectedꢀ
forꢀbulkꢀcapacitanceꢀ(atꢀappropriateꢀfrequencies),ꢀlowꢀESR,ꢀandꢀhighꢀrms-
ripple-currentꢀratings0ꢀTheꢀswitchingꢀnatureꢀofꢀDC/DCꢀconvertersꢀrequiresꢀ
thatꢀdcꢀvoltageꢀsourcesꢀhaveꢀlowꢀacꢀimpedanceꢀasꢀhighlyꢀinductiveꢀsourceꢀ
impedanceꢀcanꢀaffectꢀsystemꢀstability0ꢀInꢀFigureꢀ2,ꢀCBUSꢀandꢀLBUSꢀsimulateꢀ
aꢀtypicalꢀdcꢀvoltageꢀbus0ꢀYourꢀspecificꢀsystemꢀconfigurationꢀmayꢀnecessitateꢀ
additionalꢀconsiderations0
T E C H N I C A L N O T E S
Input Fusing
Certainꢀapplicationsꢀand/orꢀsafetyꢀagenciesꢀmayꢀrequireꢀtheꢀinstallationꢀofꢀ
fusesꢀatꢀtheꢀinputsꢀofꢀpowerꢀconversionꢀcomponents0ꢀꢀFusesꢀshouldꢀalsoꢀbeꢀ
usedꢀifꢀtheꢀpossibilityꢀofꢀsustained,ꢀnon-current-limited,ꢀinput-voltageꢀpolartiyꢀ
reversalꢀexists0ꢀForꢀC&DꢀBWRꢀꢁ±-ꢁ7ꢀWattꢀDC/DCꢀConverters,ꢀyouꢀshouldꢀ
useꢀslow-blowꢀtypeꢀfusesꢀwithꢀvaluesꢀnoꢀgreaterꢀthanꢀtheꢀfollowing:
ꢀ
Model
Fuse Value
TO
CURRENT
PROBE
OSCILLOSCOPE
ꢀ
ꢀ
ꢀ
ꢀ
AllꢀDꢁ2AꢀModelsꢀ
4ꢀAmp
2ꢀAmpꢀ
BWR-±/ꢁ±55-D24Aꢀ
+INPUT
–INPUT
LBUS
BWR-ꢁ2/72±-D24A,ꢀBWR-ꢁ±/±7±-D24Aꢀ 20±ꢀAmpꢀ
AllꢀD48AꢀModelsꢀ ꢁꢀAmp
+
V
IN
C
BUS
CIN
–
Start-Up Time
TheꢀVINꢀtoꢀVOUTꢀstart-upꢀtimeꢀisꢀtheꢀintervalꢀofꢀtimeꢀwhereꢀtheꢀinputꢀvoltageꢀ
crossesꢀtheꢀturn-onꢀthresholdꢀpoint,ꢀandꢀtheꢀfullyꢀloadedꢀoutputꢀvoltageꢀ
entersꢀandꢀremainsꢀwithinꢀitsꢀspecifiedꢀaccuracyꢀband0ꢀActualꢀmeasuredꢀ
timesꢀwillꢀvaryꢀwithꢀexternalꢀoutputꢀcapacitanceꢀandꢀload0ꢀꢀTheꢀBWRꢀ
ꢁ±-ꢁ7WꢀSeriesꢀimplementsꢀaꢀsoftꢀstartꢀcircuitꢀthatꢀlimitsꢀtheꢀdutyꢀcycleꢀꢀ
ofꢀtheꢀPWMꢀcontrollerꢀatꢀpowerꢀup,ꢀtherebyꢀlimitingꢀtheꢀInputꢀInrushꢀcurrent0ꢀ
C
IN = 33µF, ESR < 700m7 @ 100kHz
BUS = 220µF, ESR < 100m7 @ 100kHz
C
L
BUS = 12µH
Figure ꢀ. Measuring Input Ripple Current
Inꢀcriticalꢀapplications,ꢀoutputꢀripple/noiseꢀ(alsoꢀreferredꢀtoꢀasꢀperiodicꢀandꢀ
randomꢀdeviationsꢀorꢀPARD)ꢀmayꢀbeꢀreducedꢀbelowꢀspecifiedꢀlimitsꢀusingꢀ
filteringꢀtechniques,ꢀtheꢀsimplestꢀofꢀwhichꢀisꢀtheꢀinstallationꢀofꢀadditionalꢀ
externalꢀoutputꢀcapacitors0ꢀTheseꢀoutputꢀcapsꢀfunctionꢀasꢀtrueꢀfilterꢀelementsꢀ
andꢀshouldꢀbeꢀselectedꢀforꢀbulkꢀcapacitance,ꢀlowꢀESRꢀandꢀappropriateꢀ
frequencyꢀresponse0ꢀAllꢀexternalꢀcapacitorsꢀshouldꢀhaveꢀappropriateꢀvoltageꢀ
ratingsꢀandꢀbeꢀlocatedꢀasꢀcloseꢀtoꢀtheꢀconverterꢀasꢀpossible0ꢀTemperatureꢀ
variationsꢀforꢀallꢀrelevantꢀparametersꢀshouldꢀalsoꢀbeꢀtakenꢀcarefullyꢀintoꢀ
consideration0ꢀ
TheꢀOn/OffꢀControlꢀtoꢀVOUTꢀstart-upꢀtimeꢀassumesꢀtheꢀconverterꢀhasꢀitsꢀ
nominalꢀinputꢀvoltageꢀappliedꢀbutꢀisꢀturnedꢀoffꢀviaꢀtheꢀOn/OffꢀControlꢀpin0ꢀꢀ
Theꢀspecificationꢀdefinesꢀtheꢀintervalꢀbetweenꢀtheꢀtimeꢀatꢀwhichꢀtheꢀconverterꢀ
isꢀturnedꢀonꢀandꢀꢀtheꢀfullyꢀloadedꢀoutputꢀvoltageꢀentersꢀandꢀremainsꢀwithinꢀ
itsꢀspecifiedꢀaccuracyꢀband0ꢀSimilarꢀtoꢀtheꢀVINꢀtoꢀVOUTꢀstart-up,ꢀtheꢀOn/Offꢀ
ControlꢀtoꢀVOUTꢀstart-upꢀtimeꢀisꢀalsoꢀgovernedꢀbyꢀtheꢀinternalꢀsoftꢀstartꢀ
circuitryꢀandꢀexternalꢀloadꢀcapacitance0ꢀ
Input Overvoltage/Undervoltage Shutdown and Start-Up Threshold
TheꢀmostꢀeffectiveꢀcombinationꢀofꢀexternalꢀI/Oꢀcapacitorsꢀwillꢀbeꢀaꢀfunctionꢀ
ofꢀlineꢀvoltageꢀandꢀsourceꢀimpedance,ꢀasꢀwellꢀasꢀparticularꢀloadꢀandꢀlayoutꢀ
conditions0ꢀOurꢀApplicationsꢀEngineersꢀcanꢀrecommendꢀpotentialꢀsolutionsꢀ
andꢀdiscussꢀtheꢀpossibilityꢀofꢀourꢀmodifyingꢀaꢀgivenꢀdevice'sꢀinternalꢀfilteringꢀ
toꢀmeetꢀyourꢀspecificꢀrequirements0ꢀContactꢀourꢀApplicationsꢀEngineeringꢀ
Groupꢀforꢀadditionalꢀdetails0ꢀ
Underꢀnormalꢀstart-upꢀconditions,ꢀdevicesꢀwillꢀnotꢀbeginꢀtoꢀregulateꢀuntilꢀ
theꢀramping-upꢀinputꢀvoltageꢀexceedsꢀtheꢀStart-UpꢀThresholdꢀVoltageꢀ(3±Vꢀ
forꢀD48ꢀmodels)0ꢀOnceꢀoperating,ꢀdevicesꢀwillꢀnotꢀturnꢀoffꢀuntilꢀtheꢀinputꢀvolt-
ageꢀdropsꢀbelowꢀtheꢀUndervoltageꢀShutdownꢀlimitꢀ(330±VꢀforꢀD48ꢀmodels)0ꢀ
Subsequentꢀre-startꢀwillꢀnotꢀoccurꢀuntilꢀtheꢀinputꢀisꢀbroughtꢀbackꢀupꢀtoꢀtheꢀ
Start-UpꢀThreshold0ꢀꢀThisꢀbuiltꢀinꢀhysteresisꢀpreventsꢀanyꢀunstableꢀon/offꢀ
situationsꢀfromꢀoccurringꢀatꢀaꢀsingleꢀinputꢀvoltage0
Floating Outputs
SinceꢀtheseꢀareꢀisolatedꢀDC/DCꢀconverters,ꢀtheirꢀoutputsꢀareꢀ"floating,"ꢀwithꢀ
respectꢀtoꢀtheꢀinput0ꢀAsꢀsuch,ꢀitꢀisꢀpossibleꢀtoꢀuseꢀ+Output,ꢀ–OutputꢀorꢀOutputꢀ
Returnꢀasꢀtheꢀsystemꢀgroundꢀtherebyꢀallowingꢀtheꢀflexibilityꢀtoꢀgenerateꢀaꢀ
varietyꢀofꢀoutputꢀvoltageꢀcombinations0
Inputꢀvoltagesꢀexceedingꢀtheꢀinputꢀovervoltageꢀshutdownꢀspecificationꢀlistedꢀ
inꢀtheꢀPerformance/FunctionalꢀSpecificationsꢀwillꢀcauseꢀtheꢀdeviceꢀtoꢀshut-
down0ꢀAꢀbuilt-inꢀhysteresisꢀofꢀ506ꢀtoꢀꢁ06ꢀVoltsꢀforꢀallꢀmodelsꢀwillꢀnotꢀallowꢀtheꢀ
converterꢀtoꢀrestartꢀuntilꢀtheꢀinputꢀvoltageꢀisꢀsufficientlyꢀreduced0
RegulationꢀforꢀBWRꢀꢁ±-ꢁ7Wꢀbipolarꢀconvertersꢀisꢀmonitoredꢀbetweenꢀꢀ
–Outputꢀandꢀ+Outputꢀ(asꢀopposedꢀtoꢀOutputꢀtoꢀReturn)0
Input Source Impedance
Theꢀconvertersꢀmustꢀbeꢀdrivenꢀfromꢀaꢀlowꢀac-impedanceꢀinputꢀsource0ꢀTheꢀ
DC/DC'sꢀperformanceꢀandꢀstabilityꢀcanꢀbeꢀcompromisedꢀbyꢀtheꢀuseꢀofꢀhighlyꢀ
inductiveꢀsourceꢀimpedances0ꢀTheꢀinputꢀcircuitꢀshownꢀinꢀFigureꢀ2ꢀisꢀaꢀpracticalꢀ
solutionꢀthatꢀcanꢀbeꢀusedꢀtoꢀminimizeꢀtheꢀeffectsꢀofꢀinductanceꢀinꢀtheꢀinputꢀ
traces0ꢀForꢀoptimumꢀperformance,ꢀcomponentsꢀshouldꢀbeꢀmountedꢀcloseꢀtoꢀ
theꢀDC/DCꢀconverter0ꢀIfꢀtheꢀapplicationꢀhasꢀaꢀhighꢀsourceꢀimpedance,ꢀlowꢀVINꢀ
modelsꢀcanꢀbenefitꢀofꢀincreasedꢀexternalꢀinputꢀcapacitance0
Minimum Loading Requirements
BWRꢀꢁ±-ꢁ7Wꢀconvertersꢀemployꢀaꢀclassicalꢀdiode-rectificationꢀdesignꢀtopol-
ogyꢀandꢀrequireꢀaꢀminimumꢀꢁ5ꢂꢀloadingꢀtoꢀachieveꢀtheirꢀlistedꢀregulationꢀ
specificationsꢀandꢀaꢀstableꢀoperatingꢀcondition0
Load Regulation
RegulationꢀforꢀtheꢀBWRꢀꢁ±-ꢁ7Wꢀbipolarꢀconvertersꢀisꢀmonitoredꢀbetweenꢀ
–Outputꢀandꢀ+Outputꢀ(asꢀopposedꢀtoꢀOutputꢀtoꢀReturn)0ꢀAsꢀsuchꢀregulationꢀ
willꢀassureꢀthatꢀvoltageꢀbetweenꢀ–Outputꢀandꢀ+Outputꢀpinsꢀremainsꢀwithinꢀtheꢀ
VOUTꢀaccuracyꢀlistedꢀinꢀtheꢀPerformance/FunctionalꢀSpecificationsꢀtable0ꢀ
I/O Filtering5 Input Ripple Current5 and Noise Reduction
AllꢀBWRꢀꢁ±-ꢁ7WꢀDC/DCꢀConvertersꢀachieveꢀtheirꢀratedꢀrippleꢀandꢀnoiseꢀ
specificationsꢀwithoutꢀtheꢀuseꢀofꢀexternalꢀinput/outputꢀcapacitors0ꢀꢀInꢀcriticalꢀ
applications,ꢀinput/outputꢀrippleꢀandꢀnoiseꢀmayꢀbeꢀfurtherꢀreducedꢀbyꢀinstall-
ingꢀadditionalꢀexternalꢀI/Oꢀcaps0
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