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7.1Overview
7.2PSCandPLLCOverview
Overview
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Inmanyapplications,theremaybespecificrequirementstominimizepowerconsumptionforbothpower
supply(orbattery)andthermalconsiderations.Therearetwocomponentstopowerconsumption:active
powerandleakagepower.Activepoweristhepowerconsumedtoperformworkandscalesroughlywith
clockfrequencyandtheamountofcomputationsbeingperformed.Activepowercanbereducedby
controllingtheclocksinsuchawayeithertooperateataclocksettingjusthighenoughtocompletethe
requiredoperationintherequiredtimelineortorunataclocksettinguntiltheworkiscompleteandthen
drasticallycuttheclocks(thatis,toPLLBypassmode)untiladditionalworkmustbeperformed.Leakage
powerisduetostaticcurrentleakageandoccursregardlessoftheclockrate.Leakage,orstandbypower,
isunavoidablewhilepowerisappliedandscalesroughlywiththeoperatingjunctiontemperatures.
Leakagepowercanonlybeavoidedbyremovingpowercompletelyfromadevice.
TheTMS320DM646xDMSoChasseveralmeansofmanagingthepowerconsumption,asdetailedinthe
followingsections.Thereisextensiveuseofautomaticclockgatinginthedesignaswellas
software-controlledmoduleclockgatingtonotonlyreducetheclocktreepower,buttoalsoreduce
modulepowerbybasicallyfreezingitsstatewhilenotoperating.Clockmanagementallowsyoutoslow
downtheclocksonthechipinordertoreduceswitchingpower.Inparticular,theDM646xDMSoC
includesallofthepowermanagementfeaturesdescribedinTable7-1.
Table7-1.PowerManagementFeatures
PowerManagementFeaturesDescription
ClockManagement
PLLpower-downThePLLscanbepowered-downwhennotinusetoreduceswitchingpower
ModuleclockON/OFFModuleclockscanbeturnedon/offtoreduceswitchingpower
ModuleclockfrequencyscalingModuleclockfrequencycanbescaledtoreduceswitchingpower
ARMandDSPSleepManagement
ARMWait-for-InterruptsleepmodeDisableARMclocktoreduceactivepower
DSPsleepmodesTheDSPcanbeputintosleepmodetoreduceswitchingpower
I/OManagement
3.3VoltI/Opower-downThe3.3VI/Oscanbepowered-downtoreduceI/Ocellpower
USBPhypower-downTheUSBPhycanbepowered-downtoreduceUSBI/Opower
Thepowerandsleepcontroller(PSC)playsanimportantroleinmanagingsystemclockon/off,andreset.
Similarly,thePLLcontroller(PLLC)playsanimportantroleindeviceclockgeneration.ThePSCandthe
PLLCarementionedthroughoutthischapter.FordetailedinformationonthePSC,seeChapter6.For
detailedinformationonthePLLC,seeChapter5andthedevice-specificdatamanual.
80PowerManagementSPRUEP9A–May2008
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