Datasheet

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OvercurrentProtection
OutputVoltageLimitations
T
HICCUP(ms)
+
2250
ƒ
s(kHz)
(6)
SettingtheOutputVoltage
R2 +
R1 0.891
V
O
* 0.891
(7)
TPS54550
SLVS623A–MARCH2006–REVISEDAPRIL2006
OUTPUTVOLTAGE(V)R2VALUE(kΩ)
1.228.7
Overcurrentprotectionisimplementedbysensing
1.514.7
thedrain-to-sourcevoltageacrossthehigh-side
1.89.76
MOSFETandcomparedtoavoltagelevelwhich
representstheovercurrentthresholdlimit.Ifthe
2.55.49
drain-to-sourcevoltageexceedstheovercurrent
3.33.74
thresholdlimitformorethan100ns,thehigh-side
MOSFETisdisable,theSSENApinispulledlow,
andtheinternaldigitalslow-startisresetto0V.
SSENAisheldlowforapproximatelythetimethatis
DuetotheinternaldesignoftheTPS54550thereare
calculatedbyEquation6:
bothupperandloweroutputvoltagelimitsforany
giveninputvoltage.Additionally,thelowerboundary
oftheoutputvoltagesetpointrangealsodepends
onoperatingfrequency.Theupperlimitoftheoutput
voltagesetpointisconstrainedbythemaximumduty
Oncethehiccuptimeiscomplete,theSSENApinis
cycleofthedeviceandisshowninFigure12.The
releasedandtheconverterinitiatestheinternal
lowerlimitisconstrainedbytheminimum
slow-start.
controllableontime,whichmaybeashighas220
ns.Theapproximateminimumoutputvoltagefora
giveninputvoltageandrangeofoperating
TheoutputvoltageoftheTPS54550canbesetby
frequenciesisshowninFigure8,whilethemaximum
feedingbackaportionoftheoutputtotheVSENSE
operatingfrequencyversusinputvoltageforsome
pinusingaresistordividernetwork.Intheapplication
commonoutputvoltagesisshowninFigure10.
circuitofFigure29,thisdividernetworkiscomprised
Thecurvesshowninthesetwofiguresarevalidfor
ofresistorsR1andR2.Tocalculatetheresistor
outputcurrentsgreaterthan0.5A.Asoutput
valuestogeneratetherequiredoutputvoltageuse
currentsdecreasetowardsnoload(0A),the
thefollowingequation:
minimumoutputvoltagedecreases.Forapplications
wheretheloadcurrentislessthan100mA,the
curvesshowninFigure9andFigure11are
applicable.Allofthedataplottedinthesecurvesare
StartwithafixedvalueofR1andcalculatethe
approximateandtakeintoaccountapossible20%
requiredR2value.Assumingafixedvalueof10kΩ
deviationinactualoperatingfrequencyrelativetothe
forR1,thefollowingtablegivestheappropriateR2
intendedsetpoint.
valueforseveralcommonoutputvoltages:
12
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