Technical
Specification
IQ18-QTC Family
Beforeꢀtimeꢀt0,ꢀwhenꢀtheꢀinputꢀvoltageꢀisꢀbelowꢀtheꢀUVLꢀthreshold,ꢀ
theꢀunitꢀisꢀdisabledꢀbyꢀtheꢀInputꢀUnder-VoltageꢀLockoutꢀfeature.ꢀ
Whenꢀ theꢀ inputꢀ voltageꢀ risesꢀ aboveꢀ theꢀ UVLꢀthreshold,ꢀ theꢀ
InputꢀUnder-VoltageꢀLockoutꢀisꢀreleased,ꢀandꢀaꢀStartupꢀInhibitꢀ
Periodꢀisꢀinitiated.ꢀꢀAtꢀtheꢀendꢀofꢀthisꢀdelay,ꢀtheꢀON/OFFꢀpinꢀisꢀ
evaluated,ꢀandꢀsinceꢀitꢀisꢀactive,ꢀtheꢀunitꢀturnsꢀon.
maximumꢀpowerꢀtheꢀconverterꢀcanꢀdissipateꢀforꢀaꢀgivenꢀthermalꢀ
conditionꢀifꢀitsꢀbase-plateꢀisꢀtoꢀbeꢀnoꢀhigherꢀthanꢀ100ꢀºC.
100ꢀºCꢀ-ꢀTA
ꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀPmaxꢀ=ꢀ
ꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀdissꢀꢀꢀꢀꢀꢀꢀRTH
BA
Thisꢀvalueꢀofꢀpowerꢀdissipationꢀcanꢀthenꢀbeꢀusedꢀinꢀconjunctionꢀ
withꢀtheꢀdataꢀshownꢀinꢀFigureꢀ2ꢀtoꢀdetermineꢀtheꢀmaximumꢀloadꢀ
currentꢀ(andꢀpower)ꢀthatꢀtheꢀconverterꢀcanꢀdeliverꢀinꢀtheꢀgivenꢀ
thermalꢀcondition.
Atꢀtimeꢀt1,ꢀtheꢀunitꢀisꢀdisabledꢀbyꢀtheꢀON/OFFꢀpin,ꢀandꢀitꢀcannotꢀ
beꢀenabledꢀagainꢀuntilꢀtheꢀStartupꢀInhibitꢀPeriodꢀhasꢀelapsed.
Whenꢀ theꢀ ON/OFFꢀ pinꢀ goesꢀ highꢀ afterꢀ t2,ꢀ theꢀ Startupꢀ Inhibitꢀ
Periodꢀhasꢀelapsed,ꢀandꢀtheꢀoutputꢀturnsꢀonꢀwithinꢀtheꢀtypicalꢀ
Turn-OnꢀTime.
Forꢀconvenience,ꢀFiguresꢀ3ꢀandꢀ4ꢀprovideꢀPowerꢀderatingꢀcurvesꢀ
forꢀanꢀencasedꢀconverterꢀwithoutꢀaꢀheatsinkꢀandꢀwithꢀaꢀtypicalꢀ
1/4"ꢀhighꢀheatsink.
Thermal Considerations:ꢀ Theꢀ maximumꢀ operatingꢀ base-
plateꢀtemperature,ꢀTB,ꢀisꢀ100ꢀºC.ꢀAsꢀlongꢀasꢀtheꢀuser’sꢀthermalꢀ
systemꢀ keepsꢀ TBꢀ <ꢀ 100ꢀ ºC,ꢀ theꢀ converterꢀ canꢀ deliverꢀ itsꢀ fullꢀ
ratedꢀpower.
Aꢀpowerꢀderatingꢀcurveꢀcanꢀbeꢀcalculatedꢀforꢀanyꢀheatsinkꢀthatꢀisꢀ
attachedꢀtoꢀtheꢀbase-plateꢀofꢀtheꢀconverter.ꢀItꢀisꢀonlyꢀnecessaryꢀ
toꢀdetermineꢀtheꢀthermalꢀresistance,ꢀRTHBA,ꢀofꢀtheꢀchosenꢀheatsinkꢀ
betweenꢀtheꢀbase-plateꢀandꢀtheꢀambientꢀairꢀforꢀaꢀgivenꢀairflowꢀ
rate.ꢀ Thisꢀ informationꢀ isꢀ usuallyꢀ availableꢀ fromꢀ theꢀ heatsinkꢀ
vendor.ꢀTheꢀfollowingꢀformulaꢀcanꢀtheꢀbeꢀusedꢀtoꢀdetermineꢀtheꢀ
V
in
Under-Voltageꢀ
LockoutꢀTurn-
OnꢀThreshold
ON/OFF
(negꢀlogic)
ON
OFF
ON
OFF
ON
9msꢀ(typical
turnꢀonꢀtime)
V
out
200ms
(typicalꢀstart-upꢀ
inhibitꢀperiod)
200ms
200ms
t
t0
t1
t2
Figure F: Startup Inhibit Period (turn-on time not to scale)
Product # IQ18xxxQTCxx
Phone 1-888-567-9596
www.synqor.com
Doc.# 005-IQ18QTX Rev. B
09/23/08
Page 27
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