Input:

Output:

Current:

Package:

18-36 V

28 V

Half-brick

Technical Specification

Toincreasetheoutputvoltage,theusershouldconnectaresistor

betweenPin7(TRIM)andPin8(SENSE(+)input).Foradesired

increaseofthenominaloutputvoltage,thevalueoftheresistor

shouldbe

FigureBgraphstherelationshipbetweenthetrimresistorvalue,

Rtrim-upandRtrim-down,showingthetotalrangetheoutputvolt-

agecanbetrimmedupordown.

Note:TheTRIMfeaturedoesnotaffectthevoltageatwhichthe

output over-voltage protection circuit is triggered. Trimming the

output voltage too high may cause the over-voltage protection

circuittoengage,particularlyduringtransients.

ItisnotnecessaryfortheusertoaddcapacitanceattheTrimpin.

Thenodeisinternallyfilteredtoeliminatenoise.

Total DC Variation of Vout:Fortheconvertertomeetitsfull

specifications, the maximum variation of the DC value of Vout,

duetobothtrimmingandremoteloadvoltagedrops,shouldnot

begreaterthanthatspecifiedfortheoutputvoltagetrimrange.

PROTECTIONFEATURES

Input Under-Voltage Lockout: The converter is designed

to turn off when the input voltage is too low, helping to avoid

an input system instability problem, which is described in more

detailintheapplicationnotetitled“InputSystemInstability” on

theSynQorwebsite.Thelockoutcircuitryisacomparatorwith

DChysteresis.Whentheinputvoltageisrising,itmustexceedthe

typical“Turn-OnVoltageThreshold”value*beforetheconverter

willturnon.Oncetheconverterison,theinputvoltagemustfall

below the typical Turn-Off Voltage Threshold value before the

converterwillturnoff.

Output Current Limit:Iftheoutputcurrentexceedsthe“Output

DCCurrentLimitInception”point*,thenafastlinearcurrentlimit

controller will reduce the output voltage to maintain a constant

outputcurrent.Ifasaresult,theoutputvoltagefallsbelowthe

“Output DCCurrent Limit Shutdown Voltage”* for more than

50ms,thentheunitwillenterintohiccupmode,witha500ms

off-time.Theunitwillthenautomaticallyattempttorestart.

Back-Drive Current Limit:Ifthereisnegativeoutputcurrent

of a magnitude larger than the “Back-Drive Current Limit while

Enabled”specification*,thenafastback-drivelimitcontrollerwill

increasetheoutputvoltagetomaintainaconstantoutputcurrent.

If this results in the output voltage exceeding the “Output Over-

VoltageProtection”threshold*,thentheunitwillshutdown.The

fullI-VoutputcharacteristicscanbeseeninFigure15.

Output Over-Voltage Limit: If the voltage directly across

the output pins exceeds the “Output Over-Voltage Protection”

threshold*, the converter will immediately stop switching. This

shutdownislatching;unlikeothershutdowntypes,theconverter

willnotrestartunlesstheinputpoweriscycledortheON/OFF

inputistoggled.

Over-Temperature Shutdown:Atemperaturesensoronthe

convertersensestheaveragetemperatureofthemodule.Thether-

malshutdowncircuitisdesignedtoturntheconverteroffwhenthe

temperatureatthesensedlocationreachesthe“Over-Temperature

Shutdown” value*. It will allow the converter to turn on again

whenthetemperatureofthesensedlocationfallsbytheamountof

the“Over-TemperatureShutdownRestartHysteresis”value*.

*SeeElectricalCharacteristicspage.

kW

=

Vnominal

1.225

–2

)

(

0.0

0.1

1.0

10.0

100.0

1,000.0

10,000.0

100,000.0

0

5

10

15

20

25

30

35

40

45

50

% Increase in Vout

% Decrease in Vout

Figure B: Trim Graph for 28 Vout module

APPLICATIONCONSIDERATIONS

Input System Instability:Thisconditioncanoccurbecause

any DC-DC converter appears incrementally as a negative

resistanceload.Adetailedapplicationnotetitled“InputSystem

Instability”isavailableontheSynQorwebsitewhichprovides

anunderstandingofwhythisinstabilityarises,andshowsthe

preferredsolutionforcorrectingit.

Application Circuits:FigureCbelowprovidesatypicalcircuit

diagramwhichdetailstheinputfilteringandvoltagetrimming.

Input Filtering and External Input Capacitance:FigureD

belowshowstheinternalinputfiltercomponents.Thisfilterdra-

matically reduces input terminal ripple current, which otherwise

couldexceedtheratingofanexternalelectrolyticinputcapacitor.

Therecommendedexternalinputcapacitanceisspecifiedinthe

InputCharacteristicssectionontheElectricalSpecificationspage.

More detailed information is available in the application note

titled“EMICharacteristics”ontheSynQorwebsite.

Output Filtering and External Output Capacitance:

FigureDbelowshowstheinternaloutputfiltercomponents.This

filterdramaticallyreducesoutputvoltageripple.However,some

minimumexternaloutputcapacitanceisrequired,asspecifiedin

theOutputCharacteristicssectionontheElectricalSpecifications

page.Nodamagewilloccurwithoutthiscapacitorconnected,

butpeakoutputvoltageripplewillbemuchhigher.

External

Input

Filter

Trim

L

or

ON/OFF

Electrolytic

Capacitor

Figure D: Typical application circuit (negative logic unit, permanently enabled).

C

Product # IQ24280HEC14

Phone 1-888-567-9596

www.synqor.com

Doc.# 005-IHE2428 Rev. B

09/19/08

Page 10