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7.1Overview
7.2PSCandPLLCOverview
Overview
Inmanyapplications,theremaybespecificrequirementstominimizepowerconsumptionforbothpower
supply(orbattery)andthermalconsiderations.Therearetwocomponentstopowerconsumption:active
powerandleakagepower.Activepoweristhepowerconsumedtoperformworkandscalesroughlywith
clockfrequencyandtheamountofcomputationsbeingperformed.Activepowercanbereducedby
controllingtheclocksinsuchawayastoeitheroperateataclocksettingjusthighenoughtocomplete
therequiredoperationintherequiredtimelineortorunataclocksettinguntiltheworkiscompleteand
thendrasticallycuttheclocks(thatis,toPLLBypassmode)untiladditionalworkmustbeperformed.
Leakagepowerisduetostaticcurrentleakageandoccursregardlessoftheclockrate.Leakage,or
standbypower,isunavoidablewhilepowerisappliedandscalesroughlywiththeoperatingjunction
temperatures.Leakagepowercanonlybeavoidedbyremovingpowercompletelyfromadeviceor
subsystem.
TheTMS320DM643xDMPhasseveralmeansofmanagingthepowerconsumption,asdetailedinthe
followingsections.Thereisextensiveuseofautomaticclockgatinginthedesignaswellas
software-controlledmoduleclockgatingtonotonlyreducetheclocktreepower,buttoalsoreduce
modulepowerbybasicallyfreezingitsstatewhilenotoperating.Clockmanagementenablesyoutoslow
theclocksdownonthechipinordertoreduceswitchingpower.Inparticular,theDM643xDMPincludes
allofthepowermanagementfeaturesdescribedinTable7-1.
Table7-1.PowerManagementFeatures
PowerManagementFeaturesDescription
ClockManagement
PLLpower-downThePLLscanbepowered-downwhennotinusetoreduceswitchingpower
ModuleclockON/OFFModuleclockscanbeturnedon/offtoreduceswitchingpower
ModuleclockfrequencyscalingModuleclockfrequencycanbescaledtoreduceswitchingpower
DSPSleepManagement
DSPsleepmodesTheDSPcanbeputintosleepmodetoreduceswitchingpower
I/OManagement
3.3VoltI/Opower-downThe3.3VI/Oscanbepowered-downtoreduceI/Ocellpower
DACpower-downTheDAC'scanbepowered-downtoreduceDACpower
Thepowerandsleepcontroller(PSC)playsanimportantroleinmanagingsystempoweron/off,clock
on/off,andreset.Similarly,thePLLcontroller(PLLC)playsanimportantroleindeviceclockgeneration.
ThePSCandthePLLCarementionedthroughoutthischapter.FordetailedinformationonthePSC,see
Chapter6.FordetailedinformationonthePLLC,seeChapter4andChapter5.
PowerManagement 78SPRU978E–March2008
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