Technical
Specification
IQ18-QTC Family
Startup Inhibit Period:ꢀTheꢀStartupꢀInhibitꢀPeriodꢀensuresꢀthatꢀ
theꢀconverterꢀwillꢀremainꢀoffꢀforꢀapproximatelyꢀ200ꢀmsꢀwhenꢀitꢀisꢀ
shutꢀdownꢀforꢀanyꢀreason.ꢀꢀWhenꢀanꢀoutputꢀshortꢀisꢀpresent,ꢀthisꢀ
generatesꢀ aꢀ 5ꢀ Hzꢀ “hiccupꢀ mode,”ꢀ whichꢀ preventsꢀ theꢀ converterꢀ
fromꢀoverheating.ꢀꢀInꢀall,ꢀthereꢀareꢀsevenꢀwaysꢀthatꢀtheꢀconverterꢀ
canꢀbeꢀshutꢀdown,ꢀinitiatingꢀaꢀStartupꢀInhibitꢀPeriod:
APPLICATIONꢀCONSIDERATIONS
Input System Instability:ꢀThisꢀconditionꢀcanꢀoccurꢀbecauseꢀ
anyꢀ dc-dcꢀ converterꢀ appearsꢀ incrementallyꢀ asꢀ aꢀ negativeꢀ
resistanceꢀ load.ꢀ Aꢀ detailedꢀ applicationꢀ noteꢀ titledꢀ “Inputꢀ
SystemꢀInstability”ꢀisꢀavailableꢀonꢀtheꢀSynQorꢀwebsiteꢀwhichꢀ
providesꢀanꢀunderstandingꢀofꢀwhyꢀthisꢀinstabilityꢀarises,ꢀandꢀ
showsꢀtheꢀpreferredꢀsolutionꢀforꢀcorrectingꢀit.
•ꢀInputꢀUnder-VoltageꢀLockout
•ꢀOutputꢀOver-VoltageꢀProtection
•ꢀOverꢀTemperatureꢀShutdown
•ꢀCurrentꢀLimit
ꢂpplication Circuits:ꢀ Figureꢀ Dꢀ providesꢀ aꢀ typicalꢀ ꢀ circuitꢀ
diagramꢀwhichꢀdetailsꢀtheꢀinputꢀfilteringꢀandꢀvoltageꢀtrimming.ꢀ
Input Filtering and ꢁxternal Capacitance:ꢀFigureꢀEꢀprovidesꢀ
aꢀdiagramꢀshowingꢀtheꢀinternalꢀinputꢀfilterꢀcomponents.ꢀꢀThisꢀfilterꢀ
dramaticallyꢀreducesꢀinputꢀterminalꢀrippleꢀcurrent,ꢀwhichꢀotherwiseꢀ
couldꢀexceedꢀtheꢀratingꢀofꢀanꢀexternalꢀelectrolyticꢀinputꢀcapacitor.ꢀ
Theꢀrecommendedꢀexternalꢀinputꢀcapacitanceꢀisꢀspecifiedꢀinꢀtheꢀ
Inputꢀ Characteristicsꢀ sectionꢀ onꢀ theꢀ Electricalꢀ Characteristicsꢀ
page.ꢀ ꢀ Moreꢀ detailedꢀ informationꢀ isꢀ availableꢀ inꢀ theꢀ applicationꢀ
noteꢀtitledꢀ“EMIꢀCharacteristics”ꢀonꢀtheꢀSynQorꢀwebsite.
•ꢀShortꢀCircuitꢀProtection
•ꢀTurnedꢀoffꢀbyꢀtheꢀON/OFFꢀinput
FigureꢀFꢀshowsꢀthreeꢀturn-onꢀscenarios,ꢀwhereꢀaꢀStartupꢀInhibitꢀ
Periodꢀisꢀinitiatedꢀatꢀt0,ꢀt1,ꢀandꢀt2:
Vout(+)
Vin(+)
Vsense(+)
Electrolyticꢀ
Capacitor
External
Input
Filter
R
trim-up
or
Vin
Trim
ON/OFF
C
R
load
trim-down
Iload
_
Vsense( )
_
_
Vin( )
Vout( )
Figure D: Typical application circuit (negative logic unit, permanently enabled).
L
Vin(+)
C
_
Vin( )
Figure E: Internal Input Filter Diagram (component values listed on the specifications page).
Product # IQ18xxxQTCxx
Phone 1-888-567-9596
www.synqor.com
Doc.# 005-IQ18QTX Rev. B
09/23/08
Page 26
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