loadingDAC0830SeriesApplicationHints
(Continued)
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FIGURE15.SingleSupplyDACwithLevelShiftandSpan-AdjustableOutput
GainandLinearityErrorVariationvs.SupplyVoltage
GainandLinearityErrorVariationvs.ReferenceVoltage
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Note:Forthesecurves,VREFisthevoltageappliedtopin11(IOUT1)withpin12(IOUT2)grounded.
FIGURE17.
FIGURE16.
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DAC0830SeriesApplicationHints
(Continued)
GainandLinearityErrorVariationvs.Temperature
theoutputoftheopamptobiasnearthenegativesupplypo-tential.NoharmisdonetotheDAC,however,astheon-chip15k?feedbackresistorsufficientlylimitsthecurrentflowfromIOUT1whenthisleadisinternallyclampedtoonediodedropbelowground.
Carefulcircuitconstructionwithminimizationofleadlengthsaroundtheanalogcircuitry,isaprimaryconcern.Goodhighfrequencysupplydecouplingwillaidinpreventinginadvert-antnoisefromappearingontheanalogoutput.
Overallnoisereductionandreferencestabilityisofparticularconcernwhenusingthehigheraccuracyversions,theDAC0830andDAC0831,ortheiradvantagesarewasted.3.0GENERALAPPLICATIONIDEAS
Theconnectionsforthecontrolpinsofthedigitalinputregis-tersarepurposelyomitted.Anyofthecontrolformatsdis-cussedinSection1oftheaccompanyingtextwillworkwithanyofthecircuitsshown.Themethoduseddependsontheoverallsystemprovisionsandrequirements.
ThedigitalinputcodeisreferredtoasDandrepresentsthedecimalequivalentvalueofthe8-bitbinaryinput,forex-ample:
BinaryInput
Pin13MSB11000
10000
10000
10100
10000
10000
Pin7LSB10010
10000
DDecimalEquivalent
2551281620
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FIGURE18.
2.8MiscellaneousApplicationHints
TheseconvertersareCMOSproductsandreasonablecareshouldbeexercisedinhandlingthemtopreventcatastrophicfailuresduetostaticdischarge.
Conversionaccuracyisonlyasgoodastheappliedrefer-encevoltagesoprovidingastablesourceovertimeandtem-peraturechangesisanimportantfactortoconsider.A“good”groundismostdesirable.Asinglepointgrounddis-tributiontechniqueforanalogsignalsandsupplyreturnskeepsotherdevicesinasystemfromaffectingtheoutputoftheDACs.
Duringpower-upsupplyvoltagesequencing,the?15V(or?12V)supplyoftheopampmayappearfirst.Thiswillcause
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Applications
DACControlledAmplifier(VolumeControl)
CapacitanceMultiplier
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VariablefO,VariableQO,ConstantBWBandpassFilter
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Applications
(Continued)
DACControlledFunctionGenerator
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Applications
(Continued)
TwoTerminalFloating4to20mACurrentLoopController
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????
DAC0830linearlycontrolsthecurrentflowfromtheinputterminaltotheoutputterminaltobe4mA(forD=0)to19.94mA(forD=255).
Circuitoperateswithaterminalvoltagedifferentialof16Vto55V.
P2adjuststhemagnitudeoftheoutputcurrentandP1adjuststhezerotofullscalerangeofoutputcurrent.
DigitalinputscanbesuppliedfromaprocessorusingoptoisolatorsoneachinputortheDAClatchescanflow-through(con-nectcontrollinestopins3and10oftheDAC)andtheinputdatacanbesetbySPSTtoggleswitchestoground(pins3and10).
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