Datasheet

www.ti.com
Internal Oscillator
V
O(PH)
V
O(SYNC)
PowerGood(PWRGD)
BootstrapVoltage(BOOT)
ErrorAmplifier
VoltageReference
T
delay
+
1000
ƒ
s(kHz)
ms
(5)
BiasVoltage(VBIAS)
TPS54550
SLVS623A–MARCH2006–REVISEDAPRIL2006
Figure4.SYNCOutputWaveform
Upto1mAofcurrentcanbedrawnforuseinan
externalapplicationcircuit.TheVBIASpinmusthave
abypasscapacitorvalueof1.0μF.X7RorX5R
TheVSENSEpiniscomparedtoaninternal
gradedielectricceramiccapacitorsare
referencesignal.IftheVSENSEisgreaterthan97%
recommendedbecauseofthestablecharacteristics
andnootherfaultsarepresent,thePWRGDpin
overtemperature.
presentsahighimpedance.AlowonthePWRGD
pinindicatesafault.ThePWRGDpinhasbeen
designedtoprovideaweakpull-downandindicates
afaultevenwhenthedeviceisunpowered.IftheTheBOOTcapacitorobtainsitschargecycleby
TPS54550haspowerandhasanyfaultflagset,thecyclefromtheVBIAScapacitor.Acapacitorand
TPS54550indicatesthepowerisnotgoodbydrivingsmallvalueresistorfromtheBOOTpintothePH
thePWRGDpinlow.Thefollowingevents,aloneorpinsarerequiredforoperation.Thebootstrap
incombination,indicatepowerisnotgood:connectionforthehigh-sidedrivermusthavea
bypasscapacitorof0.1μFand24-Ωresistor.
•VSENSEpinoutofbounds
•Overcurrent
•Thermalshutdown
TheVSENSEpinistheerroramplifierinvertinginput.
•UVLOundervoltage
Theerroramplifierisatruevoltageamplifierwith1.5
•Inputvoltagenotpresent(weakpull-down)
mAofdrivecapabilitywithaminimumof60dBof
•Slow-starting
open-loopvoltagegainandaunitygainbandwidthof
•VBIASvoltageislow
2MHz.
OncethePWRGDpinpresentsahighimpedance
(i.e.,powerisgood),aVSENSEpinoutofbounds
conditionforcesPWRGDpinlow(i.e.,powerisbad)
Thevoltagereferencesystemproducesaprecision
afteratimedelay.Thistimedelayisafunctionofthe
referencesignalbyscalingtheoutputofa
switchingfrequencyandiscalculatedusing
temperaturestablebandgapcircuit.During
Equation5:
productiontesting,thebandgapandscalingcircuits
aretrimmedtoproduce0.891Vattheoutputofthe
erroramplifier,withtheamplifierconnectedasa
voltagefollower.Thetrimprocedureimprovesthe
regulation,sinceitcancelsoffseterrorsinthescaling
anderroramplifiercircuits.
TheVBIASregulatorprovidesastablesupplyforthe
internalanalogcircuitsandthelow-sidegatedriver.
10
SubmitDocumentationFeedback