Datasheet

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Power-OnReset
VoltageTranslation
V (V)
CC
V (V)
pass
2
1
1.5
4.5
3.5
2.5
5
4
3
2
2.5 3 3.5 4 4.5 5 5.5
Typical
Maximum
Minimum
I = 100 A
SW
out
- m
BusTransactions
Writes
PCA9548A
8-CHANNELI
2
CSWITCH
WITHRESET
SCPS143C–OCTOBER2006–REVISEDJUNE2007
Whenpower(from0V)isappliedtoV
CC
,aninternalpower-onresetholdsthePCA9548Ainaresetcondition
untilV
CC
hasreachedV
POR
.Atthatpoint,theresetconditionisreleasedandthePCA9548AregistersandI
2
C
statemachineinitializetotheirdefaultstates.Afterthat,V
CC
mustbeloweredtobelow0.2Vandthenbackup
totheoperatingvoltageforapower-resetcycle.
Thepass-gatetransistorsofthePCA9548AareconstructedsuchthattheV
CC
voltagecanbeusedtolimitthe
maximumvoltagethatispassedfromoneI
2
Cbustoanother.Figure6showsthevoltagecharacteristicsofthe
pass-gatetransistors(notethatthegraphwasgeneratedusingthedataspecifiedintheElectrical
Characteristicssectionofthisdatasheet).
Figure6.Pass-GateVoltagevsSupplyVoltageatThreeProcessPoints
ForthePCA9548Atoactasavoltagetranslator,theV
o(sw)
voltagemustbeequalto,orlowerthan,thelowest
busvoltage.Forexample,ifthemainbusisrunningat5Vandthedownstreambusesare3.3Vand2.7V,
V
o(sw)
shouldbeequaltoorbelow2.7Vtoeffectivelyclampthedownstreambusvoltages.Asshownin
Figure6,V
o(sw)
(max)is2.7VwhenthePCA9548Asupplyvoltageis3.5Vorlower,sothePCA9548Asupply
voltagecanbesetto3.3V.Pullupresistorsthencanbeusedtobringthebusvoltagestotheirappropriate
levels(seeFigure11).
DataisexchangedbetweenthemasterandPCA9548Athroughwriteandreadcommands.
DataistransmittedtothePCA9548Abysendingthedeviceaddressandsettingtheleast-significantbit(LSB)to
alogic0(seeFigure4fordeviceaddress).Thecommandbyteissentaftertheaddressanddetermineswhich
SCn/SDnchannelreceivesthedatathatfollowsthecommandbyte(seeFigure7).Thereisnolimitationonthe
numberofdatabytessentinonewritetransmission.
8
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