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5.3.1Power-SupplySequencing
TMS320DM355
DigitalMediaSystem-on-Chip(DMSoC)
SPRS463A–SEPTEMBER2007–REVISEDSEPTEMBER2007
Inordertoensuredevicereliability,theDM355requiresthefollowingpowersupplypower-onand
power-offsequences.SeetableTable5-1foradescriptionofDM355powersupplies.
Power-On:
1.Poweron1.3V:CV
DD
,V
DDA_PLL1/2
,V
DDD13_USB
,V
DDA13_USB
2.Poweron1.8V:V
DD_DDR
,V
DDA18
,V
DDA18_DAC
3.Poweron3.3V:D
VDD
,V
DDA33_DDRDLL
,V
DDA33_USB
,V
DDA33_USB_PLL
,V
DD_VIN
,V
DD_VOUT
Youmaypower-onthe1.8Vand3.3Vpowersuppliessimultaneously.
Power-Off:
1.Poweroff3.3V:D
VDD
,V
DDA33_DDRDLL
,V
DDA33_USB
,V
DDA33_USB_PLL
,V
DD_VIN
,V
DD_VOUT
2.Poweroff1.8V:V
DD_DDR
,V
DDA18
,V
DDA18_DAC
3.Poweroff1.3V:CV
DD
,V
DDA_PLL1/2
,V
DDD13_USB
,V
DDA13_USB
Youmaypower-offthe1.8Vand3.3Vpowersuppliessimultaneously.
NotethatwhenbootingtheDM355fromOneNAND,youmustensurethattheOneNANDdeviceisready
withvalidprograminstructionsbeforetheDM355attemptstoreadprograminstructionsfromit.In
particular,beforeyoureleaseDM355reset,youmustallowtimeforOneNANDdevicepowertostabilize
andfortheOneNANDdevicetocompleteitsinternalcopyroutine.Duringtheinternalcopyroutine,the
OneNANDdevicecopiesbootcodefromitsinternalnon-volatilememorytoitsinternalbootmemory
section.Boarddesignerstypicallyachievethisrequirementbydesignofthesystempowerandreset
supervisorcircuit.RefertoyourOneNANDdevicedatasheetforOneNANDpowerrampandstabilization
timesandforOneNANDbootcopytimes.
5.3.1.1Power-SupplyDesignConsiderations
CoreandI/OsupplyvoltageregulatorsshouldbelocatedclosetotheDM355tominimizeinductanceand
resistanceinthepowerdeliverypath.Additionally,whendesigningforhigh-performanceapplications
utilizingthedevice,thePCboardshouldincludeseparatepowerplanesforcore,I/O,andground,all
bypassedwithhigh-qualitylow-ESL/ESRcapacitors.
5.3.1.2Power-SupplyDecoupling
Inordertoproperlydecouplethesupplyplanesfromsystemnoise,placeasmanycapacitors(caps)as
possiblecloseto.Thesecapsneedtobeclosetothepowerpins,nomorethan1.25cmmaximum
distancetobeeffective.Physicallysmallercaps,suchas0402,arebetterbecauseoftheirlowerparasitic
inductance.Propercapacitancevaluesarealsoimportant.Smallbypasscaps(near560pF)shouldbe
closesttothepowerpins.Mediumbypasscaps(220nForaslargeascanbeobtainedinasmall
package)shouldbenextclosest.TIrecommendsnolessthan8smalland8mediumcapspersupplybe
placedimmediatelynexttotheBGAvias,usingthe"interior"BGAspaceandatleastthecornersofthe
"exterior".
Largercapsforeachsupplycanbeplacedfurtherawayforbulkdecoupling.Largebulkcaps(ontheorder
of100μF)shouldbefurthestaway,butstillascloseaspossible.Largecapsforeachsupplyshouldbe
placedoutsideoftheBGAfootprint.
Anycapselectionneedstobeevaluatedfromayield/manufacturingpoint-of-view.Aswiththeselectionof
anycomponent,verificationofcapacitoravailabilityovertheproduct’sproductionlifetimeshouldbe
considered.SeealsoSection5.5.1andSection5.5.2foradditionalrecommendationsonpowersupplies
fortheoscillator/PLLsupplies.
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