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C
T
(nf)
t
D
(s)
0.5
10
3
(s)
175
(1)
1.2v 3.3v
TPS3808G12 TPS3808G33 DSP
SENSE V
DD
V
DD
SENSE
V
i/o
V
核心
GPIO
GNDGNDGND
重置 MR
C
T
C
T
重置
IMMUNITYTOSENSEPINVOLTAGE
3.3v
TP S3808xxx
V
DD
SENSE
C
T
90k
Ω
G ND
SELECTINGTHERESETDELAYTIME
延迟 (s) = c
T
(nf) + 0.5 x 10
−3
(s)
20ms 延迟
300ms 延迟
(c)
(b)
(一个)
175
3.3v
TPS3808G33
V
DD
SENSE
C
T
重置
3.3v
TPS3808G33
V
DD
SENSE
C
T
C
T
重置
3.3v
TPS3808G33
V
DD
SENSE
C
T
50k
Ω
重置
TPS3808
SBVS050E–MAY2004–REVISEDOCTOBER2005
bythechoiceofresistor.Figure14bshowsafixed
20msdelaytimebyleavingtheC
T
pinopen.
Figure14cshowsagroundreferencedcapacitor
connectedtoC
T
forauser-definedprogramtime
between1.25msand10s.
ThecapacitorC
T
shouldbe
≥
100pFnominalvaluein
orderfortheTPS3808xxxtorecognizethatthe
capacitorispresent.thecapacitorvalueforagiven
delaytimecanbecalculatedusingthefollowing
等式:
Theresetdelaytimeisdeterminedbythetimeit
figure12.usingmrtomonitormultiplesystem
takesanon-chipprecision220nacurrentsourceto
电压
chargetheexternalcapacitorto1.23v.whena
resetisassertedthecapacitorisdischarged.当
theresetconditionsarecleared,theinternal
currentsourceisenabledandbeginstochargethe
externalcapacitor.whenthevoltageonthiscapacitor
reaches1.23v,resetisde-asserted.notethata
lowleakagetypecapacitorsuchasaceramicshould
beused,andthatstraycapacitancearoundthispin
maycauseerrorsintheresetdelaytime.
过往旅客
TheTPS3808isrelativelyimmunetoshortnegative
figure13.usinganexternalmosfettominimize
transientsonthesensepin.sensitivitytotransients
I
DD
WhenMRSignalDoesNotGotoV
DD
isdependentonthresholdoverdrive,asshowninthe
MaximumTransientDurationatSensevsSense
ThresholdOverdriveVoltage
图表(Figure6)inthe
typicalcharacteristicssection.
TheTPS3808hasthreeoptionsforsettingthe
RESETdelaytimeasshowninFigure14.Figure14一个
showstheconfigurationforafixed300mstypical
delaytimebytyingC
T
toV
DD
;aresistorfrom40k
Ω
至
200k
Ω
mustbeused.supplycurrentisnotaffected
figure14.configurationusedtosettheresetdelaytime
9
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