TPS40200-EP中文资料(12)

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SGLS371–JANUARY2007

GENERALINFORMATION(continued)

VFigure26.Current-LimitReset

Ifnecessary,asmallR-Cfiltercanbeaddedtothecurrent-sensingnetworktoreducenuisancetrippingduetonoisepickup.Thisfilteralsocanbeusedtotrimtheovercurrenttrippointtoahigherlevelwiththeadditionofasingleresistor.SeeFigure27ThenominalovercurrenttrippointusingthecircuitofFigure27isdescribedas:

VR+RF2

IOC=ILIM´F1

RILIMRF2(3)Where:

IOC=Overcurrenttrippoint,peakcurrentintheinductor

VILIM=OvercurrentthresholdvoltagefortheTPS40200,typically100mVRILIM=Valueofthecurrentsenseresistor(in )RandR=Valuesofthescalingresistors(in )

ThevalueofthecapacitorisdeterminedbythenominalpulsewidthoftheconverterandthevaluesofthescalingresistorsRF1andRF2.Itisbestnottohavethetimeconstantofthefilterlongerthanthenominalpulsewidthoftheconverter,ingthisconstraint,thecapacitorvaluemaybeboundedby:.

VOR´Rf2

Cf£÷f1

VIN´fSWRf1+Rf2(4)Where:

Cf=Valueofthecurrent-limitfiltercapacitor(inF)VO=OutputvoltageoftheconverterVIN=InputvoltagetotheconverterfSW=Converterswitchingfrequency

Rf1andRf2=Valuesofthescalingresistors(in )

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