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DEVICEOPERATION
SENSEINPUT
RESETOUTPUT
V
在
TPS3808G01
V
DD
SENSE
地
重置
R
1
R
2
1nF
V
它
′
= (1 + )0.405
R
1
R
2
V
输出
manualreset(mr)输入
2.5v
TPS 380 8G25 O M AP 1510
V
DD
SENSE
V
DDSHV 1, 3, 6, 7, 9
GNDGND
C
T
MR
重置
1M
Ω
RESPWRON
TPS3808
SBVS050E–MAY2004–REVISEDOCTOBER2005
supplylinecanbeusedtoallowtheresetsignalfor
TheTPS3808microprocessorsupervisoryproduct
themicroprocessortohaveavoltagehigherthanV
DD
familyisdesignedtoassertaRESETsignalwhen
(upto6.5v).thepull-upresistorshouldbeno
eithertheSENSEpinvoltagedropsbelowV
它
orthe
smallerthan10k
Ω
asaresultofthefiniteimpedance
manualreset(mr)isdrivenlow.theresetoutput
oftheresetline.
remainsassertedforauser-adjustabletimeafterboth
themanualreset(mr)andsensevoltagesreturn
abovetheirthresholds.abroadrangeofvoltage
thresholdandresetdelaytimeadjustmentsare
TheSENSEinputprovidesaterminalatwhichany
有,allowingthesedevicestobeusedinawide
systemvoltagecanbemonitored.ifthevoltageon
arrayofapplications.resetthresholdvoltagescanbe
thispindropsbelowV
它
,thenresetisasserted.
工厂-setfrom0.82vto3.3vorfrom4.4vto5.0v,
thecomparatorhasabuilt-inhysteresistoensure
whiletheTPS3808G01canbesettoanyvoltage
smoothresetassertionsandde-assertions.itis
above0.405vusinganexternalresistordivider.二
goodanalogdesignpracticetoputa1nFto10nF
presetdelaytimesarealsouser-可选择的:
bypasscapacitorontheSENSEinputtoreduce
connectingtheC
T
pintoV
DD
resultsina300msreset
sensitivitytotransientsandlayoutparasitics.
延迟,whileleavingthec
T
pinopenyieldsa20ms
TheTPS3808G01canbeusedtomonitorany
resetdelay.inaddition,connectingacapacitor
voltageraildownto0.405vusingthecircuitshownin
betweenC
T
andGNDallowsthedesignertoselect
Figure11.
anyresetdelayperiodfrom1.25msto10s.
AtypicalapplicationoftheTPS3808G25usedwith
theOMAP1510processorisshowninFigure10.这
opendrainRESEToutputistypicallyconnectedto
theresetinputofamicroprocessor.apull-向上
resistormustbeusedtoholdthislinehighwhen
resetisnotasserted.theresetoutputis
undefinedforvoltagebelow0.8v,butthisisnormally
notaproblemsincemostmicroprocessorsdonot
functionbelowthisvoltage.resetremainshigh
figure11.usingthetps3808g01tomonitora
(unasserted)aslongassenseisaboveitsthreshold
用户-definedthresholdvoltage
(v
它
)andthemanualreset(mr)islogichigh.ifeither
SENSEfallsbelowV
它
ormrisdrivenlow,resetis
asserted,drivingtheresetpintoalowimpedance.
themanualreset(mr)inputallowsaprocessoror
otherlogiccircuitstoinitiateareset.alogiclow
(0.3v
DD
)onmrcausesresettoassert.aftermr
returnstoalogichighandSENSEisaboveitsreset
门槛,resetisde-assertedaftertheuser
definedresetdelayexpires.notethatmrisinternally
tiedtoV
DD
usinga90k
Ω
resistorsothispincanbe
leftunconnectedifmrwillnotbeused.
看Figure12forhowMRcanbeusedtomonitor
multiplesystemvoltages.notethatifthelogicsignal
figure10.typicalapplicationofthetps3808
drivingMRdoesnotgofullytoV
DD
,therewillbe
withanOMAPProcessor
someadditionalcurrentdrawintoV
DD
asaresultof
theinternalpull-upresistoronmr.tominimize
OnceMRisagainlogichighandSENSEisaboveV
它
currentdraw,alogic-levelfetcanbeusedas
+V
HYS
(thethresholdhysteresis),adelaycircuitis
illustratedinFigure13.
enabledwhichholdsRESETlowforaspecifiedreset
delayperiod.oncetheresetdelayhasexpired,这
resetpingoestoahighimpedancestate.这
拉-upresistorfromtheopendrainresettothe
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