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7.2RecommendedClockandControlSignalTransitionBehavior
7.3PowerSupplies
7.3.1Power-SupplySequencing
DV
DD33
CV
DD12
All other
power supplies
1
2
7.3.2Power-SupplyDecoupling
7.3.3Power-DownOperation
SM320C6455-EP
FIXED-POINTDIGITALSIGNALPROCESSOR
SPRS462B–SEPTEMBER2007–REVISEDJANUARY2008
AllclocksandcontrolsignalsmusttransitionbetweenV
IH
andV
IL
(orbetweenV
IL
andV
IH
)inamonotonic
manner.
TIrecommendsthepower-supplysequenceshowninFigure7-5.AftertheDV
DD33
supplyisstable,the
remainingpowersuppliescanbepoweredupatthesametimeasCV
DD
aslongastheirsupplyvoltage
neverexceedstheCV
DD
voltageduringpowerup.SomeTIpower-supplydevicesincludefeaturesthat
facilitatepowersequencing;forexample,Auto-TrackorSlow-Start/Enablefeatures.Formoreinformation,
visitwww.ti.com/dsppower.
Figure7-5.Power-SupplySequence
Table7-2.TimingRequirementsforPower-SupplySequence
-720
-850
A-1000/-1000
NO.UNIT
-1200
MINMAX
1t
su(DVDD33-CVDD12)
Setuptime,DV
DD33
supplystablebeforeCV
DD12
supplystable0.5200ms
2t
su(CVDD12-ALLSUP)
Setuptime,CV
DD12
supplystablebeforeallothersuppliesstable0200ms
Toproperlydecouplethesupplyplanesfromsystemnoise,placeasmanycapacitors(caps)aspossible
closetotheDSP.ThesecapsneedtobeclosetotheDSP,nomorethan1.25cmmaximumdistanceto
beeffective.Physicallysmallercapsarebetter,suchas0402,butneedtobeevaluatedfroma
yield/manufacturingpoint-of-view.Parasiticinductancelimitstheeffectivenessofthedecoupling
capacitors,thereforephysicallysmallercapacitorsshouldbeusedwhilemaintainingthelargestavailable
capacitancevalue.Aswiththeselectionofanycomponent,verificationofcapacitoravailabilityoverthe
product'sproductionlifetimeshouldbeconsidered.
OneofthepowergoalsfortheC6455istoreducepowerdissipationduetounusedperipherals.Thereare
differentwaystopowerdownperipheralsontheC6455device.
Someperipheralscanbestaticallypowereddownatdeviceresetthroughthedeviceconfigurationpins
(seeSection3.1,DeviceConfigurationatDeviceReset).Onceinastaticpower-downstate,theperipheral
isheldinresetanditsclockisturnedoff.Peripheralscannotbeenabledoncetheyareinastatic
power-downstate.Totakeaperipheraloutofthestaticpower-downstate,adeviceresetmustbe
executedwithadifferentconfigurationpinsetting.
Afterdevicereset,allperipheralsontheC6455deviceareinadisabledstateandmustbeenabledby
softwarebeforebeingused.Itispossibletoenableonlytheperipheralsneededbytheapplicationwhile
keepingtherestdisabled.Notethatperipheralsinadisabledstateareheldinresetwiththeirclocks
gated.Formoreinformationonhowtoenableperipherals,seeSection3.3,PeripheralSelectionAfter
DeviceReset.
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