Datasheet

MinimizingI
CC
WhenI/OIsUsedtoControlLED
V
C
C
V
CC
LED
Pn
100 kW
V
C
C
3.3 V 5 V
LED
Pn
PCA9555
www.ti.com .........................................................................................................................................................SCPS131E–AUGUST2005–REVISEDMAY2008
WhenanI/OisusedtocontrolanLED,normallyitisconnectedtoV
CC
througharesistorasshowninFigure15.
BecausetheLEDactsasadiode,whentheLEDisoff,theI/OV
IN
isabout1.2VlessthanV
CC
.TheΔI
CC
parameterinElectricalCharacteristicsshowshowI
CC
increasesasV
IN
becomeslowerthanV
CC
.For
battery-poweredapplications,itisessentialthatthevoltageofI/OpinsisgreaterthanorequaltoV
CC
whenthe
LEDisofftominimizecurrentconsumption.
Figure16showsahigh-valueresistorinparallelwiththeLED.Figure17showsV
CC
lessthantheLEDsupply
voltagebyatleast1.2V.BothofthesemethodsmaintaintheI/OV
IN
atoraboveV
CC
andpreventadditional
supplycurrentconsumptionwhentheLEDisoff.
Figure16.High-ValueResistorinParallelWithLED
Figure17.DeviceSuppliedbyLowerVoltage
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