fAios10.0.3

LowGainDriftPrecisionInstrumentationAmplifierAD8228Rev.
0InformationfurnishedbyAnalogDevicesisbelievedtobeaccurateandreliable.
However,noresponsibilityisassumedbyAnalogDevicesforitsuse,norforanyinfringementsofpatentsorotherrightsofthirdpartiesthatmayresultfromitsuse.
Specificationssubjecttochangewithoutnotice.
NolicenseisgrantedbyimplicationorotherwiseunderanypatentorpatentrightsofAnalogDevices.
Trademarksandregisteredtrademarksarethepropertyoftheirrespectiveowners.
OneTechnologyWay,P.
O.
Box9106,Norwood,MA02062-9106,U.
S.
A.
Tel:781.
329.
4700www.
analog.
comFax:781.
461.
31132008AnalogDevices,Inc.
Allrightsreserved.
FEATURESEasytousePinstrappablegainsof10and100Widepowersupplyrange:±2.
3Vto±18VDCspecifications(BGrade,G=10)2ppm/°Cgaindrift0.
02%gainerror50μVmaximuminputoffsetvoltage0.
8μV/°Cmaximuminputoffsetdrift0.
6nAmaximuminputbiascurrent100dBCMRRACspecifications650kHz,–3dBbandwidth(G=10)2V/μsslewrateLownoise8nV/√Hz,@1kHz(G=100)0.
3μVp-pfrom0.
1Hzto10Hz(G=100)APPLICATIONSWeighscalesIndustrialprocesscontrolsBridgeamplifiersPrecisiondataacquisitionsystemsMedicalinstrumentationStraingagesTransducerinterfacesGENERALDESCRIPTIONTheAD8228isahighperformanceinstrumentationamplifierwithveryhighgainaccuracy.
Becauseallgainsettingresistorsareinternalandlasertrimmed,gainaccuracyandgaindriftarebetterthancanbeachievedwithtypicalinstrumentationamplifiers.
Lowvoltageoffset,lowoffsetdrift,lowgaindrift,highgainaccuracy,andhighCMRRmakethispartanexcellentchoiceinapplicationsthatdemandthebestdcperformancepossible,suchasbridgesignalconditioning.
CONNECTIONDIAGRAM87651234–ING1G2+VSVOUTREF–VS+INTOPVIEW(NottoScale)AD822807035-001Figure1.
Table1.
InstrumentationAmplifiersbyCategoryGeneralPurposeZeroDriftMilitaryGradeLowPowerHighSpeedPGAAD82201AD82311AD620AD6271AD8250AD8221AD85531AD621AD6231AD8251AD8222AD85551AD524AD8253AD82241AD85561AD526AD8228AD85571AD6241Rail-to-railoutput.
TheAD8228operatesonbothsingleanddualsupplies.
Becausethepartcanoperateonsuppliesupto±18V,itiswellsuitedforapplicationswherehighcommon-modeinputvoltagesareencountered.
TheAD8228isavailablein8-leadMSOPandSOICpackages.
Performanceisspecifiedovertheentireindustrialtemperaturerangeof40°Cto+85°Cforallgrades.
Furthermore,theAD8228isoperationalfrom40°Cto+125°C.
Forapin-compatibleampli-fierwithsimilarspecifications,butwithagainrangeof1to1000,seetheAD8221.
AD8228*PRODUCTPAGEQUICKLINKSLastContentUpdate:02/23/2017COMPARABLEPARTSViewaparametricsearchofcomparableparts.
EVALUATIONKITSAD62x,AD822x,AD842xSeriesInAmpEvaluationBoardDOCUMENTATIONApplicationNotesAN-1401:InstrumentationAmplifierCommon-ModeRange:TheDiamondPlotDataSheetAD8228:LowGainDriftPrecisionInstrumentationAmplifierDataSheetTechnicalBooksADesigner'sGuidetoInstrumentationAmplifiers,3rdEdition,2006UserGuidesUG-261:EvaluationBoardsfortheAD62x,AD822xandAD842xSeriesTOOLSANDSIMULATIONSAD8228SPICEMacro-ModelREFERENCEMATERIALSTechnicalArticlesHigh-performanceAdderUsesInstrumentationAmplifiersDESIGNRESOURCESAD8228MaterialDeclarationPCN-PDNInformationQualityAndReliabilitySymbolsandFootprintsDISCUSSIONSViewallAD8228EngineerZoneDiscussions.
SAMPLEANDBUYVisittheproductpagetoseepricingoptions.
TECHNICALSUPPORTSubmitatechnicalquestionorfindyourregionalsupportnumber.
DOCUMENTFEEDBACKSubmitfeedbackforthisdatasheet.
ThispageisdynamicallygeneratedbyAnalogDevices,Inc.
,andinsertedintothisdatasheet.
Adynamicchangetothecontentonthispagewillnottriggerachangetoeithertherevisionnumberorthecontentoftheproductdatasheet.
Thisdynamicpagemaybefrequentlymodified.
AD8228Rev.
0|Page2of24TABLEOFCONTENTSFeatures1Applications.
1GeneralDescription.
1ConnectionDiagram1RevisionHistory2Specifications.
3Gain=103Gain=1005AbsoluteMaximumRatings.
7ThermalResistance.
7ESDCaution.
7PinConfigurationandFunctionDescriptions.
8TypicalPerformanceCharacteristics9TheoryofOperation16Architecture16SettingtheGain.
16Common-ModeInputVoltageRange.
16ReferenceTerminal17Layout17InputProtection18RadioFrequencyInterference(RFI)18ApplicationsInformation.
19DifferentialDrive19PrecisionStrainGage.
19DrivingaDifferentialADC19OutlineDimensions.
20OrderingGuide21REVISIONHISTORY7/08—Revision0:InitialVersionAD8228Rev.
0|Page3of24SPECIFICATIONSGAIN=10VS=±15V,VREF=0V,TA=25°C,RL=2kΩ,allspecificationsreferredtoinput,unlessotherwisenoted.
Table2.
ConditionsAGradeBGradeParameter(Gain=10)MinTypMaxMinTypMaxUnitCOMMON-MODEREJECTIONRATIOCMRRDCto60Hzwith1kΩSourceImbalanceVCM=10Vto+10V94100dBCMRRat2kHzVCM=10Vto+10V90100dBNOISEVIN+=VIN=VREF=0VVoltageNoisef=1kHz1515nV/√Hzf=0.
1Hzto10Hz0.
50.
5μVp-pCurrentNoisef=1kHz4040fA/√Hzf=0.
1Hzto10Hz66pAp-pVOLTAGEOFFSETReferredtoinput,VS=±5Vto±15VOffset9050μVOverTemperatureT=40°Cto+85°C180100μVAverageTCT=40°Cto+85°C1.
50.
8μV/°COffsetvs.
Supply(PSR)104120106120dBINPUTCURRENTInputBiasCurrent0.
51.
50.
40.
6nAOverTemperatureT=40°Cto+85°C2.
01nAAverageTCT=40°Cto+85°C11pA/°CInputOffsetCurrent0.
20.
60.
10.
4nAOverTemperatureT=40°Cto+85°C0.
80.
6nAAverageTCT=40°Cto+85°C11pA/°CREFERENCEINPUTRIN2020kΩIINVIN+=VIN=VREF=0V50605060μAVoltageRangeVS+VSVS+VSVGaintoOutput1±0.
00011±0.
0001V/VDYNAMICRESPONSESmallSignal3dBBandwidth650650kHzSettlingTime0.
01%10Vstep66μsSettlingTime0.
001%10Vstep99μsSlewRate22.
522.
5V/μsGAINVOUT=10Vto+10VGainError0.
070.
02%GainNonlinearityRL=10kΩ310310ppmRL=2kΩ310310ppmGainvs.
Temperature11012ppm/°CINPUTInputImpedanceDifferential100||2100||2GΩ||pFCommonMode100||2100||2GΩ||pFInputOperatingVoltageRange1VS=±2.
3Vto±5VVS+1.
9+VS1.
1VS+1.
9+VS1.
1VOverTemperatureT=40°Cto+85°CVS+2.
0+VS1.
2VS+2.
0+VS1.
2VInputOperatingVoltageRange1VS=±5Vto±18VVS+1.
9+VS1.
2VS+1.
9+VS1.
2VOverTemperatureT=40°Cto+85°CVS+2.
0+VS1.
2VS+2.
0+VS1.
2VAD8228Rev.
0|Page4of24ConditionsAGradeBGradeParameter(Gain=10)MinTypMaxMinTypMaxUnitOUTPUTRL=10kΩOutputSwingVS=±2.
3Vto±5VVS+1.
1+VS1.
2VS+1.
1+VS1.
2VOverTemperatureT=40°Cto+85°CVS+1.
4+Vs1.
3VS+1.
4+VS1.
3VOutputSwingVS=±5Vto±18VVS+1.
2+VS1.
4VS+1.
2+VS1.
4VOverTemperatureT=–40°Cto+85°CVS+1.
6+VS1.
5VS+1.
6+VS1.
5VShort-CircuitCurrent1818mAPOWERSUPPLYOperatingRangeVS=±2.
3Vto±18V±2.
3±18±2.
3±18VQuiescentCurrent0.
8510.
851mAOverTemperatureT=40°Cto+85°C11.
211.
2mATEMPERATURERANGESpecifiedPerformance40+8540+85°COperatingRange240+12540+125°C1Operatingneartheinputvoltagerangelimitmayreducetheavailableoutputrange.
SeeFigure10andFigure11fortheinputcommon-moderangevs.
outputvoltage.
2SeetheTypicalPerformanceCharacteristicssectionforexpectedoperationbetween85°Cto125°C.
AD8228Rev.
0|Page5of24GAIN=100VS=±15V,VREF=0V,TA=25°C,RL=2kΩ,allspecificationsreferredtoinput,unlessotherwisenoted.
Table3.
ConditionsAGradeBGradeParameter(Gain=100)MinTypMaxMinTypMaxUnitCOMMON-MODEREJECTIONRATIOCMRRDCto60Hzwith1kΩSourceImbalanceVCM=10Vto+10V114120dBCMRRat2kHzVCM=10Vto+10V100105dBNOISEVIN+=VIN=VREF=0VVoltageNoisef=1kHz88nV/√Hzf=0.
1Hzto10Hz0.
30.
3μVp-pCurrentNoisef=1kHz4040fA/√Hzf=0.
1Hzto10Hz66pAp-pVOLTAGEOFFSETReferredtoinput,VS=±5Vto±15VOffset9050μVOverTemperatureT=40°Cto+85°C14080μVAverageTCT=40°Cto+85°C0.
90.
5μV/°COffsetvs.
Supply(PSR)118140124140dBINPUTCURRENTInputBiasCurrent0.
51.
50.
40.
6nAOverTemperatureT=40°Cto+85°C2.
01nAAverageTCT=40°Cto+85°C11pA/°CInputOffsetCurrent0.
20.
60.
10.
4nAOverTemperatureT=40°Cto+85°C0.
80.
6nAAverageTCT=40°Cto+85°C11pA/°CREFERENCEINPUTRIN2020kΩIINVIN+=VIN=VREF=0V50605060μAVoltageRangeVS+VSVS+VSVGaintoOutput1±0.
00011±0.
0001V/VDYNAMICRESPONSESmallSignal3dBBandwidth110110kHzSettlingTime0.
01%10Vstep1313μsSettlingTime0.
001%10Vstep1515μsSlewRate22.
522.
5V/μsGAINVOUT=10Vto+10VGainError0.
10.
05%GainNonlinearityRL=10kΩ515515ppmRL=2kΩ15451545ppmGainvs.
Temperature11012ppm/°CINPUTInputImpedanceDifferential100||2100||2GΩ||pFCommonMode100||2100||2GΩ||pFInputOperatingVoltageRange1VS=±2.
3Vto±5VVS+1.
9+VS1.
1VS+1.
9+VS1.
1VOverTemperatureT=40°Cto+85°CVS+2.
0+VS1.
2VS+2.
0+VS1.
2VInputOperatingVoltageRange1VS=±5Vto±18VVS+1.
9+VS1.
2VS+1.
9+VS1.
2VOverTemperatureT=40°Cto+85°CVS+2.
0+VS1.
2VS+2.
0+VS1.
2VAD8228Rev.
0|Page6of24ConditionsAGradeBGradeParameter(Gain=100)MinTypMaxMinTypMaxUnitOUTPUTRL=10kΩOutputSwingVS=±2.
3Vto±5VVS+1.
1+VS1.
2VS+1.
1+VS1.
2VOverTemperatureT=40°Cto+85°CVS+1.
4+Vs1.
3VS+1.
4+VS1.
3VOutputSwingVS=±5Vto±18VVS+1.
2+VS1.
4VS+1.
2+VS1.
4VOverTemperatureT=40°Cto+85°CVS+1.
6+VS1.
5VS+1.
6+VS1.
5VShort-CircuitCurrent1818mAPOWERSUPPLYOperatingRangeVS=±2.
3Vto±18V±2.
3±18±2.
3±18VQuiescentCurrent0.
8510.
851mAOverTemperatureT=40°Cto+85°C11.
211.
2mATEMPERATURERANGESpecifiedPerformance40+8540+85°COperatingRange240+12540+125°C1Operatingneartheinputvoltagerangelimitmayreducetheavailableoutputrange.
SeeFigure12andFigure13fortheinputcommon-moderangevs.
outputvoltage.
2SeetheTypicalPerformanceCharacteristicssectionforexpectedoperationbetween85°Cto125°C.
AD8228Rev.
0|Page7of24ABSOLUTEMAXIMUMRATINGSTable4.
ParameterRatingSupplyVoltage±18VOutputShort-CircuitCurrentIndefiniteInputVoltage(CommonMode)±VSDifferentialInputVoltage±VSStorageTemperatureRange65°Cto+150°COperatingTemperatureRange140°Cto+125°CMaximumJunctionTemperature140°CESDHumanBodyModel2kVChargeDeviceModel1kV1Temperaturerangeforspecifiedperformanceis40°Cto+85°C.
SeetheTypicalPerformanceCharacteristicssectionforexpectedoperationfrom85°Cto125°C.
StressesabovethoselistedunderAbsoluteMaximumRatingsmaycausepermanentdamagetothedevice.
Thisisastressratingonly;functionaloperationofthedeviceattheseoranyotherconditionsabovethoseindicatedintheoperationalsectionofthisspecificationisnotimplied.
Exposuretoabsolutemaximumratingconditionsforextendedperiodsmayaffectdevicereliability.
THERMALRESISTANCEθJAisspecifiedforadeviceinfreeair.
Table5.
PackageθJAUnit8-LeadMSOP,4-LayerJEDECBoard135°C/W8-LeadSOIC,4-LayerJEDECBoard121°C/WESDCAUTIONAD8228Rev.
0|Page8of24PINCONFIGURATIONANDFUNCTIONDESCRIPTIONS87651234–ING1G2+VSVOUTREF–VS+INTOPVIEW(NottoScale)AD822807035-004Figure2.
PinConfigurationTable6.
PinFunctionDescriptionsPinNo.
MnemonicDescription1INNegativeInput.
2,3G1,G2GainPins.
Shorttogetherforagainof100.
Leaveunconnectedforagainof10.
4+INPositiveInput.
5VSNegativeSupply.
6REFReference.
7VOUTOutput.
8+VSPositiveSupply.
AD8228Rev.
0|Page9of24TYPICALPERFORMANCECHARACTERISTICST=25°C,VS=±15V,RL=10kΩ,unlessotherwisenoted.
706050403020100–100–50050100G10SYSTEMVOSRTI@15V(V)HITS07035-043MEAN:–5.
5SD:12.
4Figure3.
TypicalDistributionofInputOffsetVoltage(G=10)6050403020100–1.
5–1.
0–0.
500.
51.
01.
5G10SYSTEMVOSDRIFTRTI(V)HITS07035-045MEAN:–0.
079SD:0.
27Figure4.
TypicalDistributionofInputOffsetVoltageDrift(G=10)806040200–100–50050100G100SYSTEMVOSRTI@15V(V)HITS07035-046MEAN:7.
1SD:10.
1Figure5.
TypicalDistributionofInputOffsetVoltage(G=100)100806040200–1.
0–0.
500.
51.
01.
5G100SYSTEMVOSDRIFTRTI(V)HITS07035-047MEAN:0.
20SD:0.
12Figure6.
TypicalDistributionofInputOffsetVoltageDrift(G=100)100806040200–3–2–10123CMRRG100RTI(V/V)HITS07035-048MEAN:0.
29SD:0.
27Figure7.
TypicalDistributionforCMR(G=100)1001208060402001.
5–0.
500.
51.
0NEGIBIASCURRENTS±15V(nA)HITS07035-049MEAN:0.
42SD:0.
08Figure8.
TypicalDistributionofInputBiasCurrentAD8228Rev.
0|Page10of24806040200–0.
6–0.
4–0.
200.
20.
40.
6IOS@15V(nA)HITS07035-050MEAN:–0.
097SD:0.
07Figure9.
TypicalDistributionofInputOffsetCurrent543210–1–2–3–4–5–5–4–3–2–1012345OUTPUTVOLTAGE(V)INPUTCOMMON-MODEVOLTAGE(V)07035-033VS=±5VVS=±2.
5VFigure10.
InputCommon-ModeVoltagevs.
OutputVoltage,VS=±2.
5V,±5V;G=10151050–5–10–15–15–10–5051015OUTPUTVOLTAGE(V)INPUTCOMMON-MODEVOLTAGE(V)07035-034VS=±15VFigure11.
InputCommon-ModeVoltagevs.
OutputVoltage,VS=±15V,G=10543210–1–2–3–4–5–5–4–3–2–1012345OUTPUTVOLTAGE(V)INPUTCOMMON-MODEVOLTAGE(V)07035-035VS=±5VVS=±2.
5VFigure12.
InputCommon-ModeVoltagevs.
OutputVoltage,VS=±2.
5V,±5V;G=100151050–5–10–15–15–10–5051015OUTPUTVOLTAGE(V)INPUTCOMMON-MODEVOLTAGE(V)07035-036VS=±15VFigure13.
InputCommon-ModeVoltagevs.
OutputVoltage,VS=±15V,G=1000.
600.
550.
500.
450.
400.
350.
300.
250.
20–15–10–5051015COMMON-MODEVOLTAGE(V)INPUTBIASCURRENT(nA)07035-051+INIBIAS,±15VSUPPLIES–INIBIAS,±15VSUPPLIES+INIBIAS,±5VSUPPLIES–INIBIAS,±5VSUPPLIESFigure14.
InputBiasCurrentvs.
Common-ModeVoltageAD8228Rev.
0|Page11of242.
001.
751.
501.
251.
000.
750.
500.
2500.
010.
1110WARM-UPTIME(Minutes)CHANGEININPUTOFFSETVOLTAGE(V)07035-002Figure15.
ChangeinInputOffsetVoltagevs.
Warm-UpTime3210–1–2–34–4–40–20020406080100120140TEMPERATURE(°C)INPUTBIASCURRENT(nA)07035-052–INIBIAS+INIBIASIOSFigure16.
InputBiasCurrentandOffsetCurrentvs.
Temperature16014012010080604020101001k10k100k1MFREQUENCY(Hz)POSITIVEPSRR(dB)07035-012G=100G=10Figure17.
PositivePSRRvs.
Frequency,RTI160140120100806040200.
11101001k10k100k1MFREQUENCY(Hz)NEGATIVEPSRR(dB)07035-013G=100G=10Figure18.
NegativePSRRvs.
Frequency706050403020100–10–20–301001k10k100k1M10MFREQUENCY(Hz)GAIN(dB)07035-019G=100G=10Figure19.
Gainvs.
Frequency150100500–50–100–150–45–15154575105–300306090120135TEMPERATURE(°C)GAINERROR(V/V)07035-007G=100G=10Figure20.
GainErrorvs.
TemperatureAD8228Rev.
0|Page12of2414012010080604001101001k10k100k1MFREQUENCY(Hz)CMRR(dB)07035-039G=100G=10Figure21.
CMRRvs.
Frequency,RTI14012010080604001101001k10k100k1MFREQUENCY(Hz)CMRR(dB)07035-040G=100G=10Figure22.
CMRRvs.
Frequency,RTI,1kΩSourceImbalance151050–5–10–1520–20–40–20020406080100120140TEMPERATURE(°C)CMR(V/V)07035-008Figure23.
CMRvs.
Temperature+VS–0+VS–0.
4+VS–0.
8+VS–1.
2+VS–1.
6+VS–2.
0–VS+2.
0–VS+1.
6–VS+1.
2–VS+0.
8–VS+0.
4–VS+005101520SUPPLYVOLTAGE(±V)INPUTVOLTAGELIMIT(V)REFERREDTOSUPPLYVOLTAGES07035-014Figure24.
InputVoltageLimitvs.
SupplyVoltage+VS–0+VS–0.
4+VS–0.
8+VS–1.
2+VS–1.
6+VS–2.
0–VS+2.
0–VS+1.
6–VS+1.
2–VS+0.
8–VS+0.
4–VS+005101520SUPPLYVOLTAGE(±V)OUTPUTVOLTAGELIMIT(V)REFERREDTOSUPPLYVOLTAGES07035-015RL=10kRL=2kRL=10kRL=2kFigure25.
OutputVoltageSwingvs.
SupplyVoltage3025201510501101001k10kLOADRESISTANCE()OUTPUTVOLTAGE(Vp-p)07035-020VS=±15VFigure26.
OutputVoltageSwingvs.
LoadResistanceAD8228Rev.
0|Page13of24+VS–0–1–2–3+3+2+1–VS+00123456789101112OUTPUTCURRENT(mA)OUTPUTVOLTAGESWING(V)REFERREDTOSUPPLYVOLTAGE07035-021Figure27.
OutputVoltageSwingvs.
OutputCurrent,G=1–10–8–6–4–20246810OUTPUTVOLTAGE(V)07035-016ERROR(10ppm/DIV)Figure28.
GainNonlinearity,G=10,RL=10kΩ–10–8–6–4–20246810OUTPUTVOLTAGE(V)07035-029ERROR(10ppm/DIV)Figure29.
GainNonlinearity,G=100,RL=10kΩ1k1001011101001k10k100kFREQUENCY(Hz)VOLTAGENOISERTI(nV/√Hz)07035-022G=100G=10Figure30.
VoltageNoiseSpectralDensityvs.
Frequency0.
2V/DIV1s/DIV07035-023Figure31.
0.
1Hzto10HzRTIVoltageNoise,G=1010001001011101001k10kFREQUENCY(Hz)CURRENTNOISE(fA/Hz)07035-030Figure32.
CurrentNoiseSpectralDensityvs.
FrequencyAD8228Rev.
0|Page14of2407035-0315pA/DIV1s/DIVFigure33.
0.
1Hzto10HzCurrentNoise3025201510501k10k100k1MFREQUENCY(Hz)OUTPUTVOLTAGE(Vp-p)07035-024VS=±15VG=10,100Figure34.
LargeSignalFrequencyResponse5V/DIV0.
002%/DIV20s/DIV07035-025Figure35.
LargeSignalPulseResponseandSettlingTime(G=10)5V/DIV0.
002%/DIV20s/DIV07035-026Figure36.
LargeSignalPulseResponseandSettlingTime(G=100)20mV/DIV4s/DIV07035-027Figure37.
SmallSignalResponse,G=10,RL=2kΩ,CL=100pF20mV/DIV4s/DIV07035-028Figure38.
SmallSignalResponse,G=100,RL=2kΩ,CL=100pFAD8228Rev.
0|Page15of2415105OUTPUTVOLTAGESTEPSIZE(Vp-p)SETTLINGTIME(s)07035-04115105002020.
017.
515.
012.
510.
002015105OUTPUTVOLTAGESTEPSIZE(Vp-p)SETTLINGTIME(s)07035-0420.
001%SETTLINGTIMEG=10RL=10k0.
01%SETTLINGTIME0.
001%SETTLINGTIMEG=100RL=10k0.
01%SETTLINGTIMEFigure39.
SettlingTimevs.
StepSize,G=10Figure40.
SettlingTimevs.
StepSize,G=100AD8228Rev.
0|Page16of24THEORYOFOPERATIONC1C2IIIBCOMPENSATIONIBCOMPENSATIONVBIASA1A2A3R4489G1G2GAINSETR34.
889kR222kR122kV1V2+VS+VS–VS+VS–VSQ1Q2600–VS–IN+VS600–VS+IN+VS–VS10k10k10k10k+VS–VSOUTPUTREF07035-018Figure41.
SimplifiedSchematicARCHITECTURETheAD8228isbasedontheclassicthreeopamptopology.
Thistopologyhastwostages:apreamplifiertoprovidedifferentialamplification,followedbyadifferenceamplifiertoremovethecommon-modevoltage.
Figure41showsasimplifiedschematicoftheAD8228.
ThefirststageiscomposedoftheA1andA2amplifiers,theQ1andQ2inputtransistors,andtheR1throughR4resistors.
ThefeedbackloopofA1,R1,andQ1ensuresthattheV1voltageisaconstantdiodedropbelowinthenegativeinputvoltage.
Similarly,V2iskeptaconstantdiodedropbelowthepositiveinput.
Therefore,areplicaofthedifferentialinputvoltageisplacedacrosseitherR3(whenthegainpinsareleftopen)orR3||R4(whenthegainpinsareshorted).
ThecurrentthatflowsacrossthisresistancemustalsoflowthroughtheR1andR2resistors,creatingagaineddifferentialsignalbetweentheA2andA1outputs.
Notethat,inadditiontoagaineddifferentialsignal,theoriginalcommon-modesignal,shiftedadiodedropdown,isalsostillpresent.
Thesecondstageisadifferenceamplifier,composedofA3andfour10kΩresistors.
Thepurposeofthisstageistoremovethecommon-modesignalfromtheamplifieddifferentialsignal.
TheAD8228doesnotdependonexternalresistors.
Muchofthedcperformanceofprecisioncircuitsdependsontheaccuracyandmatchingofresistors.
TheresistorsontheAD8228arelaidouttobetightlymatched.
Theresistorsofeachpartarelasertrimmedandtestedfortheirmatchingaccuracy.
Becauseofthistrimmingandtesting,theAD8228canguaranteehighaccuracyforspeci-ficationssuchasgaindrift,common-moderejection(CMRR),andgainerror.
SETTINGTHEGAINTheAD8228canbeconfiguredforagainof10or100withnoexternalcomponents.
LeavePin2andPin3openforagainof10;shortPin2andPin3togetherforagainof100(seeFigure42).
07035-003AD822812348567+VS–VSREF–IN+INAD822812348567+VS–VSREFVOUTVOUT–IN+ING=10PIN2ANDPIN3OPENG=100PIN2ANDPIN3SHORTEDFigure42.
SettingtheGainThetransferfunctionwithPin2andPin3openisVOUT=10*(VIN+VIN)+VREFThetransferfunctionwithPin2andPin3shortedisVOUT=100*(VIN+VIN)+VREFCOMMON-MODEINPUTVOLTAGERANGEThethreeopamparchitectureoftheAD8228appliesgainandthenremovesthecommon-modevoltage.
Therefore,internalnodesintheAD8228experienceacombinationofboththegainedsignalandthecommon-modesignal.
Thiscombinedsignalcanbelimitedbythevoltagesuppliesevenwhentheindividualinputandoutputsignalsarenot.
Figure10throughFigure13showtheallowablecommon-modeinputvoltagerangesforvariousoutputvoltagesandsupplyvoltages.
AD8228Rev.
0|Page17of24REFERENCETERMINALTheoutputvoltageoftheAD8228isdevelopedwithrespecttothepotentialonthereferenceterminal.
Thisisusefulwhentheoutputsignalneedstobeoffsettoaprecisemidsupplylevel.
Forexample,avoltagesourcecanbetiedtotheREFpintolevel-shifttheoutputsothattheAD8228candriveasingle-supplyADC.
TheREFpinisprotectedwithESDdiodesandshouldnotexceedeither+VSorVSbymorethan0.
3V.
Forbestperformance,sourceimpedancetotheREFterminalshouldbekeptbelow1Ω.
AsshowninFigure41,thereferenceterminal,REF,isatoneendofa10kΩresistor.
Additionalimped-anceattheREFterminaladdstothis10kΩresistorandresultsinamplificationofthesignalconnectedtothepositiveinput.
TheamplificationfromtheadditionalRREFcanbecomputedby()REFREFRR++*kΩ20kΩ102Onlythepositivesignalpathisamplified;thenegativepathisunaffected.
ThisunevenamplificationdegradestheCMRRoftheamplifier.
INCORRECTVCORRECTAD8228OP1177+–V07035-005REFAD8228REFFigure43.
DrivingtheReferenceLAYOUTTheAD8228isahighprecisiondevice.
ToensureoptimumperformanceatthePCBlevel,caremustbetakeninthedesignoftheboardlayout.
TheAD8228pinsarearrangedinalogicalmannertoaidinthistask.
87651234–ING1G2+VSVOUTREF–VS+INTOPVIEW(NottoScale)AD822807035-044Figure44.
PinoutDiagramCommon-ModeRejectionRatiooverFrequencyTheAD8228hasahigherCMRRoverfrequencythantypicalin-amps,whichgivesitgreaterimmunitytodisturbancessuchaslinenoiseanditsassociatedharmonics.
TheAD8228pinoutwasdesignedsothattheboarddesignercantakefulladvantageofthisperformancewithawell-implementedlayout.
Poorlayoutcancausesomeofthecommon-modesignaltobeconvertedtoadifferentialsignalbeforeitreachesthein-amp.
Suchconversionsoccurwhenoneinputpathhasafrequencyresponsethatisdifferentfromtheother.
TokeepCMRRacrossfrequencyhigh,inputsourceimpedanceandcapacitanceofeachpathshouldbecloselymatched.
Additionalsourceresistanceintheinputpath(forexample,forinputprotection)shouldbeplacedclosetothein-ampinputs,whichminimizestheirinteractionwithparasiticcapacitancefromthePCBtraces.
ParasiticcapacitanceatthegainsettingpinscanalsoaffectCMRRoverfrequency.
Iftheboarddesignhasacomponentatthegainsettingpins(forexample,aswitchorjumper),thepartshouldbechosensothattheparasiticcapacitanceisassmallaspossible.
PowerSuppliesAstabledcvoltageshouldbeusedtopowertheinstrumentationamplifier.
Noiseonthesupplypinscanadverselyaffectperform-ance.
SeethePSRRperformancecurvesinFigure17andFigure18formoreinformation.
A0.
1μFcapacitorshouldbeplacedascloseaspossibletoeachsupplypin.
AsshowninFigure45,a10μFtantalumcapacitorcanbeusedfartherawayfromthepart.
Inmostcases,itcanbesharedbyotherprecisionintegratedcircuits.
AD8228+VS+IN–INLOADREF0.
1F10F0.
1F10F–VSVOUT07035-006Figure45.
SupplyDecoupling,REF,andOutputReferredtoLocalGroundAD8228Rev.
0|Page18of24ReferencesTheoutputvoltageoftheAD8228isdevelopedwithrespecttothepotentialonthereferenceterminal.
CareshouldbetakentotieREFtotheappropriatelocalground.
InputBiasCurrentReturnPathTheinputbiascurrentoftheAD8228musthaveareturnpathtocommon.
Whenthesource,suchasathermocouple,cannotprovideareturncurrentpath,oneshouldbecreated,asshowninFigure46.
THERMOCOUPLE+VSREF–VSAD8228CAPACITIVELYCOUPLED+VSREFCC–VSAD8228TRANSFORMER+VSREF–VSAD8228INCORRECTCAPACITIVELYCOUPLED+VSREFCRRC–VSAD82281fHIGH-PASS=2πRCTHERMOCOUPLE+VSREF–VS10MAD8228TRANSFORMER+VSREF–VSAD8228CORRECT07035-009Figure46.
CreatinganIBIASPathINPUTPROTECTIONAllterminalsoftheAD8228areprotectedagainstESD(1kV,humanbodymodel).
Inaddition,theinputstructureallowsfordcoverloadconditionsofabout3.
5Vbeyondthesupplies.
InputVoltagesBeyondtheRailsForlargerinputvoltages,anexternalresistorshouldbeusedinserieswitheachinputtolimitcurrentduringoverloadconditions.
TheAD8228cansafelyhandleacontinuous6mAcurrent.
ThelimitingresistorcanbecomputedfromΩ600mA6≥SUPPLYINLIMITVVRForapplicationswheretheAD8228encountersextremeoverloadvoltages,suchascardiacdefibrillators,externalseriesresistorsandlowleakagediodeclampssuchastheBAV199L,theFJH1100s,ortheSP720shouldbeused.
LargeDifferentialVoltagesWhenG=100Whenoperatingatagainof100,largedifferentialinputvoltagescancausemorethan6mAofcurrenttoflowintotheinputs.
Thisconditionoccurswhenthevoltagebetween+INand–INexceeds5V.
Thisistruefordifferentialvoltagesofeitherpolarity.
Themaximumalloweddifferentialvoltagecanbeincreasedbyaddinganinputprotectionresistorinserieswitheachinput.
ThevalueofeachprotectionresistorshouldbeRPROTECT=(VDIFF_MAX5V)/6mARADIOFREQUENCYINTERFERENCE(RFI)RFrectificationisoftenaproblemwhenamplifiersareusedinapplicationshavingstrongRFsignals.
Thedisturbancecanappearasasmalldcoffsetvoltage.
Highfrequencysignalscanbefilteredwithalow-passRCnetworkplacedattheinputoftheinstru-mentationamplifier,asshowninFigure47.
Thefilterlimitstheinputsignalbandwidth,accordingtothefollowingrelationship:FilterFrequencyDIFF=)2(π21CDCCR+FilterFrequencyCM=CRCπ21whereCD≥10CC.
RRAD8228+15V+IN–IN0.
1F10F10F0.
1FREFVOUT–15VCDCCCC10nF1nF1nF07035-0104.
02k4.
02kFigure47.
RFISuppressionCDaffectsthedifferencesignal,andCCaffectsthecommon-modesignal.
ValuesofRandCCshouldbechosentominimizeRFI.
MismatchbetweentheR*CCatthepositiveinputandtheR*CCatthenegativeinputdegradestheCMRRoftheAD8228.
ByusingavalueofCDonemagnitudelargerthanCC,theeffectofthemismatchisreduced,andperformanceisimproved.
AD8228Rev.
0|Page19of24APPLICATIONSINFORMATIONDIFFERENTIALDRIVEFigure48showshowtoconfiguretheAD8228fordifferentialoutput.
TheadvantageofthiscircuitisthatthedcdifferentialaccuracydependsontheAD8228andnotontheopamportheresistors.
ThiscircuittakesadvantageoftheprecisecontroltheAD8228hasofitsoutputvoltagerelativetothereferencevoltage.
Theidealequationforthedifferentialoutputisasfollows:VDIFF_OUT=VOUT+VOUT=Gain*(VIN+VIN)Opampdcperformanceandresistormatchingdeterminethedccommon-modeoutputaccuracy.
However,becausecommon-modeerrorsarelikelytoberejectedbythenextdeviceinthesignalchain,theseerrorstypicallyhavelittleeffectonoverallsystemaccuracy.
Theidealequationforthecommon-modeoutputisasfollows:VCM_OUT=2++OUTOUTVV=VREFForbestacperformance,anopampwithatleast3MHzgainbandwidthproductand2V/μsslewrateisrecommended.
+IN–INREFAD8228VREF10k+–AD8641+OUT–OUT07035-01710kFigure48.
DifferentialOutputUsinganOpAmpPRECISIONSTRAINGAGEThelowoffsetandhighCMRRoverfrequencyoftheAD8228makeitanexcellentcandidateforbridgemeasurements.
AsshowninFigure49,thebridgecanbeconnecteddirectlytotheinputsoftheamplifier.
5V2.
5V07035-01110F0.
1FAD8228+IN–IN350350350350+–Figure49.
PrecisionStrainGageDRIVINGADIFFERENTIALADCFigure50showshowtheAD8228canbeusedtodriveadifferentialADC.
TheAD8228isconfiguredwithanopampandtworesistorsfordifferentialdrive.
The510Ωresistorsand2200pFcapacitorsisolatetheinstrumentationamplifierfromtheswitchingtransientsproducedbytheswitchedcapacitorfrontendofatypicalSARconverter.
ThesecomponentsbetweentheADCandtheamplifieralsocreateafilterat142kHz,whichprovidesantialiasingandnoisefiltering.
TheadvantageofthisconfigurationisthatituseslesspowerthanadedicatedADCdriver:theAD8641typicallyconsumes200μA,andthecurrentthroughthetwo10kΩresistorsis250μAatfulloutputvoltage.
WiththeAD7688,thisconfigurationgivesexcellentdcperform-anceandaTHDof71dB(10kHzinput).
Forapplicationsthatneedbetterdistortionperformance,adedicatedADCdriver,suchastheADA4941-1orADA4922-1,isrecommended.
07035-032IN+VDDREFGNDAD7688IN–0.
1F+5VADR435GNDVINVOUT0.
1F+8V0.
1F10FX5R10k10k0.
1F5100.
1F5100.
1F0.
1FAD8228+IN–INREF+8V–8V0.
1F0.
1F–8V+8VAD864110k10kFigure50.
DrivingaDifferentialADCAD8228Rev.
0|Page20of24OUTLINEDIMENSIONSCOMPLIANTTOJEDECSTANDARDSMO-187-AA0.
800.
600.
408°0°4815PIN10.
65BSCSEATINGPLANE0.
380.
221.
10MAX3.
203.
002.
80COPLANARITY0.
100.
230.
083.
203.
002.
805.
154.
904.
650.
150.
000.
950.
850.
75Figure51.
8-LeadMiniSmallOutlinePackage[MSOP](RM-8)DimensionsshowninmillimetersCONTROLLINGDIMENSIONSAREINMILLIMETERS;INCHDIMENSIONS(INPARENTHESES)AREROUNDED-OFFMILLIMETEREQUIVALENTSFORREFERENCEONLYANDARENOTAPPROPRIATEFORUSEINDESIGN.
COMPLIANTTOJEDECSTANDARDSMS-012-AA012407-A0.
25(0.
0098)0.
17(0.
0067)1.
27(0.
0500)0.
40(0.
0157)0.
50(0.
0196)0.
25(0.
0099)45°8°0°1.
75(0.
0688)1.
35(0.
0532)SEATINGPLANE0.
25(0.
0098)0.
10(0.
0040)41855.
00(0.
1968)4.
80(0.
1890)4.
00(0.
1574)3.
80(0.
1497)1.
27(0.
0500)BSC6.
20(0.
2441)5.
80(0.
2284)0.
51(0.
0201)0.
31(0.
0122)COPLANARITY0.
10Figure52.
8-LeadStandardSmallOutlinePackage[SOIC_N]NarrowBody(R-8)Dimensionsshowninmillimetersand(inches)AD8228Rev.
0|Page21of24ORDERINGGUIDEModelTemperatureRangePackageDescriptionPackageOptionBrandingAD8228ARMZ1–40°Cto+85°C8-LeadMSOPRM-8Y16AD8228ARMZ-RL1–40°Cto+85°C8-LeadMSOP,13"TapeandReelRM-8Y16AD8228ARMZ-R71–40°Cto+85°C8-LeadMSOP,7"TapeandReelRM-8Y16AD8228ARZ1–40°Cto+85°C8-LeadSOIC_NR-8AD8228ARZ-RL1–40°Cto+85°C8-LeadSOIC_N,13"TapeandReelR-8AD8228ARZ-R71–40°Cto+85°C8-LeadSOIC_N,7"TapeandReelR-8AD8228BRMZ1–40°Cto+85°C8-LeadMSOPRM-8Y1MAD8228BRMZ-RL1–40°Cto+85°C8-LeadMSOP,13"TapeandReelRM-8Y1MAD8228BRMZ-R71–40°Cto+85°C8-LeadMSOP,7"TapeandReelRM-8Y1MAD8228BRZ1–40°Cto+85°C8-LeadSOIC_NR-8AD8228BRZ-RL1–40°Cto+85°C8-LeadSOIC_N,13"TapeandReelR-8AD8228ARZ-R71–40°Cto+85°C8-LeadSOIC_N,7"TapeandReelR-81Z=RoHSCompliantPart.
AD8228Rev.
0|Page22of24NOTESAD8228Rev.
0|Page23of24NOTESAD8228Rev.
0|Page24of24NOTES2008AnalogDevices,Inc.
Allrightsreserved.
Trademarksandregisteredtrademarksarethepropertyoftheirrespectiveowners.
D07035-0-7/08(0)