iC-LV
5ꢀBITꢁOPTOꢁENCODER
RevꢁA3,ꢁPageꢁ8/12
DESCRIPTION OF FUNCTIONS
Illumination control
Track evaluation
TheꢁintegratedꢁLEDꢁpowerꢁcontrolꢁwithꢁaꢁdriverꢁstage
keepsꢁ theꢁ photocurrentꢁ ofꢁ referenceꢁ photosensor
DREFꢁconstant.ꢁThisꢁcompensatesꢁforꢁaging,ꢁdirtꢁand
dropsꢁinꢁefficiencyꢁofꢁtheꢁtransmittingꢁLEDꢁwithꢁrises
inꢁtemperature.
Theꢁswitchingꢁthresholdꢁsuppliedꢁtoꢁtheꢁtrackꢁcomꢀ
paratorsꢁliesꢁatꢁhalfꢁofꢁINREF,ꢁie.ꢁinꢁtheꢁcenterꢁbeꢀ
tweenꢁaꢁfullꢁlightꢁandꢁnoꢁlightꢁcondition,ꢁandꢁadjusts
automaticallyꢁtoꢁchangesꢁinꢁillumination.ꢁThisꢁenables
theꢁ deviceꢁ toꢁ beꢁ operatedꢁ withoutꢁ theꢁ LEDꢁ power
controlꢁ withꢁ aꢁ constantꢁ illuminationꢁ levelꢁ only.ꢁ The
hysteresisꢁ ofꢁ theꢁ currentꢁ comparatorsꢁ isꢁ also
photocurrentꢁtrackedꢁandꢁincreasesꢁnoiseꢁimmunity.
TheꢁphotocurrentꢁofꢁreferenceꢁsensorꢁDREFꢁandꢁthe
darkꢁcurrentꢁofꢁcompensationꢁsensorꢁDDꢁareꢁampliꢀ
fiedꢁinꢁtheꢁreceiver.ꢁTheꢁamplifiedꢁcurrentsꢁareꢁsubꢀ
tractedꢁfromꢁoneꢁanother,ꢁyieldingꢁanꢁactualꢁvalueꢁto
feedꢁtheꢁLEDꢁpowerꢁcontrol.ꢁTheꢁcurrentꢁadjustedꢁby
resistorꢁR1ꢁatꢁpinꢁRSETꢁgeneratesꢁtheꢁbiasꢁforꢁthe
control;ꢁtheꢁvoltageꢁatꢁpinꢁRSETꢁisꢁkeptꢁconstantꢁ(see
ElectricalꢁCharacteristicsꢁNo.ꢁE01).ꢁIfꢁpinꢁRSETꢁreꢀ
mainsꢁopenꢁanꢁinternalꢁbiasꢁcurrentꢁisꢁusedꢁwhichꢁis
equivalentꢁtoꢁanꢁexternalꢁresistorꢁofꢁca.ꢁ24ꢁkꢃ.
Theꢁ mostꢁ significantꢁ bitꢁ (MSB)ꢁ canꢁ beꢁ invertedꢁ by
connectingꢁpinꢁNDIRꢁtoꢁgroundꢁ(GND).ꢁIfꢁtheꢁpinꢁreꢀ
mainsꢁopen,ꢁanꢁinternalꢁpullꢀupꢁcurrentꢁsourceꢁgenerꢀ
atesꢁaꢁhighꢁlevel.ꢁWhenꢁGrayꢁcodeꢁdiscsꢁareꢁused,
invertingꢁtheꢁMSBꢁtrackꢁisꢁtantamountꢁtoꢁchangingꢁthe
directionꢁofꢁrotation.
IfꢁthereꢁisꢁanꢁopticalꢁfeedbackꢁloopꢁfromꢁtheꢁLEDꢁto
referenceꢁsensorꢁDREFꢁtheꢁpowerꢁdriverꢁaltersꢁthe
LEDꢁcurrentꢁuntilꢁtheꢁopticalꢁpowerꢁreceivedꢁcomplies
withꢁtheꢁgivenꢁsetpoint.ꢁTheꢁphotocurrentꢁgenerated
byꢁꢁreferenceꢁsensorꢁDREFꢁBꢁandꢁthusꢁalsoꢁtheꢁlevel
ofꢁilluminationꢁforꢁtheꢁoverallꢁsystemꢁBꢁisꢁkeptꢁconꢀ
stant.
AꢁmonitoringꢁcircuitꢁdetectsꢁwhenꢁandꢁifꢁtheꢁLEDꢁconꢀ
trolꢁrangeꢁisꢁovershotꢁorꢁundershotꢁandꢁsignalsꢁthisꢁby
switchingꢁerrorꢁoutputꢁNERRꢁtoꢁlowꢁandꢁviaꢁtheꢁerror
bitꢁduringꢁserialꢁcommunicationꢁ(whenꢁSEENꢁisꢁhigh
andꢁnoꢁsynchronizationꢁisꢁselected).
ResistorꢁR3ꢁconnectedꢁinꢁseriesꢁtoꢁtheꢁtransmitting
LEDꢁlimitsꢁtheꢁcurrentꢁandꢁgovernsꢁtheꢁoperatingꢁlimꢀ
itsꢁofꢁtheꢁLEDꢁpowerꢁcontrol.
Atꢁtheꢁsameꢁtimeꢁtheꢁamplifiedꢁdarkꢁcurrentꢁofꢁcomꢀ
pensationꢁsensorꢁDDꢁandꢁtheꢁreferenceꢁphotocurrent
ofꢁsensorꢁDREFꢁareꢁaddedꢁtogether.ꢁTheꢁresulting
current,ꢁnamedꢁINREF,ꢁisꢁusedꢁtoꢁprovideꢁtheꢁswitchꢀ
ingꢁthresholdꢁforꢁtheꢁtrackꢁcomparators.ꢁThisꢁenables
operationꢁofꢁiCꢀLVꢁwithꢁanꢁexternalꢁlightꢁsourceꢁinꢀ
steadꢁofꢁusingꢁpowerꢀcontrolledꢁLED.
ICHAUS [ IC-HAUS GMBH ]
