Datasheet

MinimizingI
CC
WhenI/OsControlLEDs
LED
LEDx
V
CC
100 kW
V
CC
LED
3.3 V
5 V
LEDx
V
CC
PCA9554A
www.ti.com ...........................................................................................................................................SCPS127D–SEPTEMBER2006–REVISEDAUGUST2008
WhentheI/OsareusedtocontrolLEDs,theyarenormallyconnectedtoV
CC
througharesistorasshownin
Figure14.BecausetheLEDactsasadiode,whentheLEDisoff,theI/OV
IN
isabout1.2VlessthanV
CC
.The
supplycurrent,I
CC
,increasesasV
IN
becomeslowerthanV
CC
andisspecifiedasΔI
CC
inElectrical
Characteristics.
Forbattery-poweredapplications,itisessentialthatthevoltageofI/OpinsisgreaterthanorequaltoV
CC
when
theLEDisofftominimizecurrentconsumption.Figure15showsahigh-valueresistorinparallelwiththeLED.
Figure16showsV
CC
lessthantheLEDsupplyvoltagebyatleast1.2V.BothofthesemethodsmaintaintheI/O
V
IN
atoraboveV
CC
andpreventsadditionalsupply-currentconsumptionwhentheLEDisoff.
Figure15.High-ValueResistorinParallelWiththeLED
Figure16.DeviceSuppliedbyaLowerVoltage
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