Technical
Specification
IQ18-HPC Family
ꢃtartup Inhibit Period:ꢀTheꢀStartupꢀInhibitꢀPeriodꢀensuresꢀthatꢀ
theꢀconverterꢀwillꢀremainꢀoffꢀforꢀapproximatelyꢀ200ꢀmsꢀwhenꢀitꢀisꢀ
shut down for any reason. When an output short is present, this
generatesꢀ aꢀ 5ꢀ Hzꢀ “hiccupꢀ mode,”ꢀ whichꢀ preventsꢀ theꢀ converterꢀ
from overheating. In all, there are seven ways that the converter
canꢀbeꢀshutꢀdown,ꢀinitiatingꢀaꢀStartupꢀInhibitꢀPeriod:
APPLICATIONꢀCONSIDERATIONS
Input ꢃystem Instability: This condition can occur because
any dc-dc converter appears incrementally as a negative
resistanceꢀ load.ꢀ Aꢀ detailedꢀ applicationꢀ noteꢀ titledꢀ “Input
SystemꢀInstability”ꢀisꢀavailableꢀonꢀtheꢀSynQorꢀwebsite which
provides an understanding of why this instability arises, and
shows the preferred solution for correcting it.
•ꢀ InputꢀUnder-VoltageꢀLockout
•ꢀ InputꢀOver-VoltageꢀShutdown
•ꢀ OutputꢀOver-VoltageꢀProtection
•ꢀ OverꢀTemperatureꢀShutdown
•ꢀ CurrentꢀLimit
Application Circuits:ꢀ Figureꢀ Dꢀ providesꢀ aꢀ typicalꢀ ꢀ circuitꢀ
diagram which details the input filtering and voltage trimming.
Input Filtering and ꢂxternal Capacitance: FigureꢀE provides
a diagram showing the internal input filter components. This filter
dramatically reduces input terminal ripple current, which otherwise
could exceed the rating of an external electrolytic input capacitor.
The recommended external input capacitance is specified in the
Inputꢀ Characteristicsꢀ sectionꢀ onꢀ theꢀ Electricalꢀ Characteristicsꢀ
page.ꢀ ꢀ Moreꢀ detailedꢀ informationꢀ isꢀ availableꢀ inꢀ theꢀ applicationꢀ
note titled “EMIꢀCharacteristics”ꢀonꢀtheꢀSynQorꢀwebsite.
•ꢀ ShortꢀCircuitꢀProtection
•ꢀ TurnedꢀoffꢀbyꢀtheꢀON/OFFꢀinput
FigureꢀFꢀshowsꢀthreeꢀturn-onꢀscenarios,ꢀwhereꢀaꢀStartupꢀInhibitꢀ
Period is initiated at t0, t1, and t2:
Vout(+)
Vin(+)
Vsense(+)
Electrolytic
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 # IQ18xxxHPCxx
Phone 1-888-567-9596
www.synqor.com
Doc.# 005-005029 Rev. B
04/13/09
Page 26
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