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DETAILEDDESCRIPTION
batteryfreshnessseal(tps3619)
电源-failcomparator(pfiandpfo)
backup-batteryswitchover
tps3619-33,tps3619-50
tps3620-33,tps3620-50
SLVS387E–APRIL2001–REVISEDSEPTEMBER2004
thebatteryfreshnesssealofthetps3619familydisconnectsthebackup-batteryfrominternalcircuitryuntilitis
需要.thisfunctionpreventsthebackup-batteryfrombeingdischargedunitlthefinalproductisputtouse.这
followingstepsexplainhowtoenablethefreshnesssealmode.
1.connectv
BAT
(v
BAT
>v
BAT
最小值)
2.groundpfo
3.connectpfitov
DD
(pfi=v
DD
)
4.connectv
DD
topowersupply(v
DD
>v
它
)andkeepconnectedfor5ms<t<35ms
thebatteryfreshnesssealmodeisautomaticallyremovedbythepositive-goingedgeofresetwhenv
DD
是
应用.
anadditionalcomparatorisprovidedtomonitorvoltagesotherthanthenominalsupplyvoltage.这
电源-失败-输入(pfi)iscomparedwithaninternalvoltagereferenceof1.15v.iftheinputvoltagefallsbelowthe
电源-failthresholdv
它(pfi)
oftypical1.15v,thepower-failoutput(pfo)goeslow.ifv
它(pfi)
goesaboveV
(pfi)
,
plusabout12-mvhysteresis,theoutputreturnstohigh.byconnectingtwoexternalresistors,itispossibleto
superviseanyvoltagesaboveV
(pfi)
.thesumofbothresistorsshouldbeabout1m
Ω
,tominimizepower
consumptionandalsotoassurethatthecurrentinthePFIpincanbeignoredcomparedwiththecurrentthrough
theresistornetwork.thetoleranceoftheexternalresistorsshouldbenotmorethan1%toensureminimal
variationofsensedvoltage.ifthepower-failcomparatorisunused,pfishouldbeconnectedtogroundandpfo
leftunconnected.
incaseofabrownoutorpowerfailure,itmaybenecessarytopreservethecontentsofram.ifabackupbattery
isinstalledatV
BAT
,thedeviceautomaticallyswitchestheconnectedramtobackuppowerwhenv
DD
失败.在
ordertoallowthebackupbattery(e.g.,a3.6-vlithiumcell)tohaveahighervoltagethanv
DD
,thesesupervisors
donotconnectV
BAT
toV
输出
whenV
BAT
isgreaterthanV
DD
.v
BAT
onlyconnectstoV
输出
(througha15-
Ω
转变)
whenV
DD
fallsbelowV
它
andV
BAT
isgreaterthanV
DD
.whenv
DD
recovers,switchoverisdeferredeitheruntil
V
DD
crossesV
BAT
,oruntilv
DD
risesabovetheresetthresholdV
它
.v
输出
connectstoV
DD
througha1-
Ω
(最大值)
PMOSswitchwhenV
DD
crossestheresetthreshold.
FUNCTIONTABLE
V
DD
>v
BAT
V
DD
>v
它
V
输出
11V
DD
10V
DD
01V
DD
00V
BAT
10
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