Embedded Power for

Business-Critical Continuity

Technical Reference Note

Output Capacitance

TheLGA C Serieshasoutputcapacitorsinsidetheconverter. Limited output capacitance,10uFforthe

3A/6A/10Aand50uFforthe20A, is required for stable operation. Whenpoweringloadswithlarge

dynamiccurrentrequirements,improvedvoltageregulationis obtained by inserting low ESR capacitors

ascloseaspossibletotheload. Low ESR ceramiccapacitorswillhandletheshortdurationhigh

frequencycomponentsofthedynamiccurrentrequirement. Inaddition,highervaluesofelectrolytic

capacitorsshouldbeusedtohandlethemid-frequencycomponents.

Itisequallyimportanttousegooddesignpracticeswhenconfiguringthedcdistributionsystem. Low

resistanceandlowinductancePCBlayouttracesshouldbeutilized,particularlyinthehighcurrentoutput

section.RememberthatthecapacitanceofthedistributionsystemandtheassociatedESRarewithinthe

feedbackloopofthepowercapabilities,thusaffectingthestability and dynamic response ofthemodule.

Notethatthemaximumratedvalueofoutputcapacitancevariesbetweenmodelsandforeachoutput

voltage setpoint. A stability vs. Load Capacitance calculator,(seeyoursalesrepresentative),detailshow

anexternalloadcapacitanceinfluencesthegainandphasemarginsoftheLGA C Series modules.

Setting Margin Control

Tomargintheoutputvoltageup,pullthemargincontrolpinhigh.Tomargindown,pullthemargin

controlpinlow.Ifthepinisleftfloating,thefeatureisdisabled.Themaximummarginingrangeis±33%

oftheoutputvoltagesetting,withmaximumoutputat5.5V.Theequationsformarginingupanddown

are as follows:

Vmargin_up=0.1182* Rmargin * Rtrim+2k

Rofs+

Rtrim

Vmargin_down=0.1182* Rmargin * Rtrim+2k

Rofs-

Rtrim

Note:Themargincontrolpincannotbepulledinthefollowingrange:

If,Vin≤5VthenVmargin(max)=Vin

If,Vin>5VthenVmargin(max)=5V

See Table 1 for suggested margining values.

Rev. 12.07.09

LGA C Series

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Applications(cont'd)