leadfree

LT1991

11991fd

–

+

5V

ΔV

IN

V

M(IN)

V

P(IN)

–

+

V

OUT

=V

REF

+ΔV

IN

SWING40mVTO

EITHERRAIL

R

OUT

<0.1Ω

V

REF

=2.5V

INPUTRANGE

–0.5VTO5.1V

R

IN

=900kΩ

LT1991

1991TA01

50k

50k

150k

150k

450k

450k

4pF

450k

450k

4pF

TYPICALAPPLICATION

FEATURES

APPLICATIONS

DESCRIPTION

Precision,100µA

GainSelectableAmplifier

TheLT®1991combinesaprecisionoperationalamplifier

witheightprecisionresistorstoformaone-chipsolution

rom–13to14

withagainaccuracyof0.04%canbeachievedusingno

iceisparticularlywellsuited

foruasadifferenceamplifier,wheretheexcellentresis-

tormatchingresultsinacommonmoderejectionratioof

greaterthan75dB.

Theamplifierfeaturesa50µVmaximuminputofftvolt-

ice

operatesfromanysupplyvoltagefrom2.7Vto36Vand

drawsonly100µ

outputswingstowithin40mVofeithersupplyrail.

Theresistorshaveexcellentmatching,0.04%overtem-

chingtemperature

coefficentisguaranteedlessthan3ppm/°istors

areextremelylinearwithvoltage,resultinginagainnon-

linearityoflessthan10ppm.

TheLT1991isfullyspecifiedat5Vand±15Vsuppliesand

from–40°Cto125°iceisavailableinspace

saving10-leadMSOPandlowprofile(0.8mm)3mm×

3mmDFNpackages.

Rail-to-RailGain=1DifferenceAmplifier

■PinConfigurableasaDifferenceAmplifier,

InvertingandNoninvertingAmplifier

■DifferenceAmplifier

GainRange1to13

CMRR>75dB

■NoninvertingAmplifier

GainRange0.07to14

■InvertingAmplifier

GainRange–0.08to–13

■GainError<0.04%

■GainDrift<3ppm/°C

■WideSupplyRange:Single2.7VtoSplit±18V

■Micropower:100µASupplyCurrent

■Precision:50µVMaximumInputOfftVoltage

■560kHzGainBandwidthProduct

■Rail-to-RailOutput

■SpaceSaving10-LeadMSOPandDFNPackages

■HandheldInstrumentation

■MedicalInstrumentation

■StrainGaugeAmplifiers

■DifferentialtoSingle-EndedConversion

RESISTORMATCHING(%)

P

E

R

C

E

N

T

A

G

E

O

F

U

NI

T

S

(

%)

0.04

1991TA01b

–0.02

0

0.02

40

35

30

25

20

15

10

5

0

–0.04

450kRESISTORS

LT1991A

DistributionofResistorMatching

,LTCandLTareregisteredtrademarksofLinearTechnologyCorporation.

pending.

LT1991

21991fd

ABSOLUTEMAXIMUMRATINGS

TotalSupplyVoltage(V+toV–)................................40V

InputVoltage(PinsP1/M1,Note2).......................±60V

InputVoltage

(OtherInputsNote2).................V++0.2VtoV––0.2V

OutputShort-CircuitDuration(Note3)...........Indefinite

OperatingTemperatureRange(Note4)

LT1991C..............................................–40°Cto85°C

LT1991I...............................................–40°Cto85°C

LT1991H............................................–40°Cto125°C

(Note1)

TOPVIEW

DDPACKAGE

10-LEAD(3mm×3mm)PLASTICDFN

10

9

6

7

8

4

5

3

2

1

M1

M3

M9

V

CC

OUT

P1

P3

P9

V

EE

REF

EXPOSEDPADCONNECTEDTOV

EE

PCB

CONNECTIONOPTIONAL

T

JMAX

=125°C,θ

JA

=43°C/W

1

2

3

4

5

P1

P3

P9

V

EE

REF

10

9

8

7

6

M1

M3

M9

V

CC

OUT

TOPVIEW

MSPACKAGE

10-LEADPLASTICMSOP

T

JMAX

=150°C,θ

JA

=230°C/W

ORDERPARTNUMBERDDPARTMARKING*ORDERPARTNUMBERMSPARTMARKING*

LT1991CDD

LT1991IDD

LT1991ACDD

LT1991AIDD

LT1991HDD

LBMM

LBMM

LBMM

LBMM

LBMM

LT1991CMS

LT1991IMS

LT1991ACMS

LT1991AIMS

LT1991HM

LTQD

LTQD

LTQD

LTQD

LTQD

OrderOptionsTapeandReel:Add#TR

LeadFree:Add#PBFLeadFreeTapeandReel:Add#TRPBF

LeadFreePartMarking:/leadfree/

ConsultLTCMarketingforpartsspecifiedwithwideroperatingtemperatureranges.*Thetemperaturegradeisidentifiedbyalabelontheshippingcontainer.

SpecifiedTemperatureRange(Note5)

LT1991C..............................................–40°Cto85°C

LT1991I...............................................–40°Cto85°C

LT1991H............................................–40°Cto125°C

MaximumJunctionTemperature

DDPackage..........................................................125°C

MSPackage.........................................................150°C

StorageTemperatureRange

DDPackage............................................–65°Cto125°C

MSPackage...........................................–65°Cto150°C

LeadTemperature(Soldering,10c).................300°C

PACKAGE/ORDERINFORMATION

LT1991

31991fd

ELECTRICALCHARACTERISTICS

SYMBOLPARAMETERCONDITIONSMINTYPMAXUNITS

ΔGGainErrorV

S

=±15V,V

OUT

=±10V;R

L

=10k

G=1;LT1991A

G=1;LT1991

G=3or9;LT1991A

G=3or9;LT1991

●

●

●

●

±0.04

±0.08

±0.06

±0.12

%

%

%

%

GNLGainNonlinearityV

S

=±15V;V

OUT

=±10V;R

L

=10k●110ppm

ΔG/ΔTGainDriftvsTemperature(Note6)V

S

=±15V;V

OUT

=±10V;R

L

=10k●0.33ppm/°C

CMRRCommonModeRejectionRatio,

ReferredtoInputs(RTI)

V

S

=±15V;V

CM

=±15.2V

G=9;LT1991A

G=3;LT1991A

G=1;LT1991A

AnyGain;LT1991

●

●

●

●

80

75

75

60

100

93

90

70

dB

dB

dB

dB

V

CM

InputVoltageRange(Note7)P1/M1Inputs

V

S

=±15V;V

REF

=0V

V

S

=5V,0V;V

REF

=2.5V

V

S

=3V,0V;V

REF

=1.25V

●

●

●

–28

–0.5

0.75

27.6

5.1

2.35

V

V

V

P1/M1Inputs,P9/M9ConnectedtoREF

V

S

=±15V;V

REF

=0V

V

S

=5V,0V;V

REF

=2.5V

V

S

=3V,0V;V

REF

=1.25V

●

●

●

–60

–14

–1.5

60

16.8

7.3

V

V

V

P3/M3Inputs

V

S

=±15V;V

REF

=0V

V

S

=5V,0V;V

REF

=2.5V

V

S

=3V,0V;V

REF

=1.25V

●

●

●

–15.2

0.5

0.95

15.2

4.2

1.95

V

V

V

P9/M9Inputs

V

S

=±15V;V

REF

=0V

V

S

=5V,0V;V

REF

=2.5V

V

S

=3V,0V;V

REF

=1.25V

●

●

●

–15.2

0.85

1.0

15.2

3.9

1.9

V

V

V

V

OS

OpAmpOfftVoltage(Note8)LT1991AMS,V

S

=5V,0V

●

1550

135

µV

µV

LT1991AMS,V

S

=±15V

●

1580

160

µV

µV

LT1991MS

●

25100

200

µV

µV

LT1991DD

●

25150

250

µV

µV

ΔV

OS

/ΔTOpAmpOfftVoltageDrift(Note6)●0.31µV/°C

IBOpAmpInputBiasCurrent(Note11)

●

2.55

7.5

nA

nA

I

OS

OpAmpInputOfftCurrent(Note11)LT1991A

●

50500

750

pA

pA

LT1991

●

501000

1500

pA

pA

OpAmpInputNoiVoltage0.01Hzto1Hz

0.01Hzto1Hz

0.1Hzto10Hz

0.1Hzto10Hz

0.35

0.07

0.25

0.05

µV

P-P

µV

RMS

µV

P-P

µV

RMS

e

n

InputNoiVoltageDensityG=1;f=1kHz

G=9;f=1kHz

180

46

nV/√Hz

nV/√Hz

The●denotesthespecificationswhichapplyovertheoperating

temperaturerangeof0°Cto70°CforC-gradepartsand–40°Cto85°CforI-gradeparts,otherwispecificationsareatT

A

=25°C.

Differenceamplifierconfiguration,V

S

=5V,0Vor±15V;V

CM

=V

REF

=halfsupply,unlessotherwinoted.

LT1991

41991fd

SYMBOLPARAMETERCONDITIONSMINTYPMAXUNITS

R

IN

InputImpedance(Note10)P1(M1=Ground)

P3(M3=Ground)

P9(M9=Ground)

●

●

●

630

420

350

900

600

500

1170

780

650

kΩ

kΩ

kΩ

M1(P1=Ground)

M3(P3=Ground)

M9(P9=Ground)

●

●

●

315

105

35

450

150

50

585

195

65

kΩ

kΩ

kΩ

ΔRResistorMatching(Note9)450kResistors,LT1991A

OtherResistors,LT1991A

450kResistors,LT1991

OtherResistors,LT1991

●

●

●

●

0.01

0.02

0.02

0.04

0.04

0.06

0.08

0.12

%

%

%

%

ΔR/ΔTResistorTemperatureCoefficient(Note6)ResistorMatching

AbsoluteValue

●

●

0.3

–30

3ppm/°C

ppm/°C

PSRRPowerSupplyRejectionRatioV

S

=±1.35Vto±18V(Note8)●105135dB

MinimumSupplyVoltage●2.42.7V

V

OUT

OutputVoltageSwing(toEitherRail)NoLoad

V

S

=5V,0V

V

S

=5V,0V

V

S

=±15V

●

●

4055

65

110

mV

mV

mV

1mALoad

V

S

=5V,0V

V

S

=5V,0V

V

S

=±15V

●

●

150225

275

300

mV

mV

mV

I

SC

OutputShort-CircuitCurrent(Sourcing)DriveOutputPositive;

ShortOutputtoGround●

8

4

12mA

mA

OutputShort-CircuitCurrent(Sinking)DriveOutputNegative;

ShortOutputtoV

S

orMidsupply●

8

4

21mA

mA

BW–3dBBandwidthG=1

G=3

G=9

110

78

40

kHz

kHz

kHz

GBWPOpAmpGainBandwidthProductf=10kHz560kHz

t

r

,t

f

RiTime,FallTimeG=1;0.1VStep;10%to90%

G=9;0.1VStep;10%to90%

3

8

µs

µs

t

s

SettlingTimeto0.01%G=1;V

S

=5V,0V;2VStep

G=1;V

S

=5V,0V;–2VStep

G=1;V

S

=±15V,10VStep

G=1;V

S

=±15V,–10VStep

42

48

114

74

µs

µs

µs

µs

SRSlewRateV

S

=5V,0V;V

OUT

=1Vto4V

V

S

=±15V;V

OUT

=±10V;V

MEAS

=±5V

●

●

0.06

0.08

0.12

0.12

V/µs

V/µs

I

s

SupplyCurrentV

S

=5V,0V

●

100110

150

µA

µA

V

S

=±15V

●

130160

210

µA

µA

ELECTRICALCHARACTERISTICSThe●denotesthespecificationswhichapplyovertheoperating

temperaturerangeof0°Cto70°CforC-gradepartsand–40°Cto85°CforI-gradeparts,otherwispecificationsareatT

A

=25°C.

Differenceamplifierconfiguration,V

S

=5V,0Vor±15V;V

CM

=V

REF

=halfsupply,unlessotherwinoted.

LT1991

51991fd

ELECTRICALCHARACTERISTICS

SYMBOLPARAMETERCONDITIONSMINTYPMAXUNITS

ΔGGainErrorV

S

=±15V,V

OUT

=±10V;R

L

=10k

G=1

G=3or9

●

●

±0.08

±0.12

%

%

GNLGainNonlinearityV

S

=±15V;V

OUT

=±10V;R

L

=10k●110ppm

ΔG/ΔTGainDriftvsTemperature(Note6)V

S

=±15V;V

OUT

=±10V;R

L

=10k●0.33ppm/°C

CMRRCommonModeRejectionRatio,

ReferredtoInputs(RTI)

V

S

=±15V;V

CM

=±15.2V

G=9

G=3

G=1

●

●

●

77

70

70

100

93

90

dB

dB

dB

V

CM

InputVoltageRange(Note7)P1/M1Inputs

V

S

=±15V;V

REF

=0V

V

S

=5V,0V;V

REF

=2.5V

V

S

=3V,0V;V

REF

=1.25V

●

●

●

–28

–0.5

0.75

27.6

5.1

2.35

V

V

V

P1/M1Inputs,P9/M9ConnectedtoREF

V

S

=±15V;V

REF

=0V

V

S

=5V,0V;V

REF

=2.5V

V

S

=3V,0V;V

REF

=1.25V

●

●

●

–60

–14

–1.5

60

16.8

7.3

V

V

V

P3/M3Inputs

V

S

=±15V;V

REF

=0V

V

S

=5V,0V;V

REF

=2.5V

V

S

=3V,0V;V

REF

=1.25V

●

●

●

–15.2

0.5

0.95

15.2

4.2

1.95

V

V

V

P9/M9Inputs

V

S

=±15V;V

REF

=0V

V

S

=5V,0V;V

REF

=2.5V

V

S

=3V,0V;V

REF

=1.25V

●

●

●

–15.2

0.85

1.0

15.2

3.9

1.9

V

V

V

V

OS

OpAmpOfftVoltage(Note8)LT1991MS

●

25100

285

µV

µV

LT1991DD

●

25150

295

µV

µV

ΔV

OS

/ΔTOpAmpOfftVoltageDrift(Note6)●0.31µV/°C

IBOpAmpInputBiasCurrent(Note11)

●

2.55

15

nA

nA

I

OS

OpAmpInputOfftCurrent(Note11)

●

501000

2500

pA

pA

OpAmpInputNoiVoltage0.01Hzto1Hz

0.01Hzto1Hz

0.1Hzto10Hz

0.1Hzto10Hz

0.35

0.07

0.25

0.05

µV

P-P

µV

RMS

µV

P-P

µV

RMS

e

n

InputNoiVoltageDensityG=1;f=1kHz

G=9;f=1kHz

180

46

nV/√Hz

nV/√

Hz

R

IN

InputImpedance(Note10)P1(M1=Ground)

P3(M3=Ground)

P9(M9=Ground)

●

●

●

630

420

350

900

600

500

1170

780

650

kΩ

kΩ

kΩ

M1(P1=Ground)

M3(P3=Ground)

M9(P9=Ground)

●

●

●

315

105

35

450

150

50

585

195

65

kΩ

kΩ

kΩ

ΔRResistorMatching(Note9)450kResistors

OtherResistors

●

●

0.02

0.04

0.08

0.12

%

%

ΔR/ΔTResistorTemperatureCoefficient(Note6)ResistorMatching

AbsoluteValue

●

●

0.3

–30

3ppm/°C

ppm/°C

The●denotesthespecificationswhichapplyovertheoperating

temperaturerangeof–40°Cto125°CforH-gradeparts,otherwispecificationsareatT

A

=25°enceamplifierconfiguration,

V

S

=5V,0Vor±15V;V

CM

=V

REF

=halfsupply,unlessotherwinoted.

LT1991

61991fd

SYMBOLPARAMETERCONDITIONSMINTYPMAXUNITS

PSRRPowerSupplyRejectionRatioV

S

=±1.35Vto±18V(Note8)●105135dB

MinimumSupplyVoltage●2.42.7V

V

OUT

OutputVoltageSwing(toEitherRail)NoLoad

V

S

=5V,0V

V

S

=5V,0V

V

S

=±15V

●

●

4055

75

120

mV

mV

mV

1mALoad

V

S

=5V,0V

V

S

=5V,0V

V

S

=±15V

●

●

150225

300

340

mV

mV

mV

I

SC

OutputShort-CircuitCurrent(Sourcing)DriveOutputPositive;

ShortOutputtoGround●

8

4

12mA

mA

OutputShort-CircuitCurrent(Sinking)DriveOutputNegative;

ShortOutputtoV

S

orMidsupply●

8

4

21mA

mA

BW–3dBBandwidthG=1

G=3

G=9

110

78

40

kHz

kHz

kHz

GBWPOpAmpGainBandwidthProductf=10kHz560kHz

t

r

,t

f

RiTime,FallTimeG=1;0.1VStep;10%to90%

G=9;0.1VStep;10%to90%

3

8

µs

µs

t

s

SettlingTimeto0.01%G=1;V

S

=5V,0V;2VStep

G=1;V

S

=5V,0V;–2VStep

G=1;V

S

=±15V,10VStep

G=1;V

S

=±15V,–10VStep

42

48

114

74

µs

µs

µs

µs

SRSlewRateV

S

=5V,0V;V

OUT

=1Vto4V

V

S

=±15V;V

OUT

=±10V;V

MEAS

=±5V

●

●

0.06

0.08

0.12

0.12

V/µs

V/µs

I

s

SupplyCurrentV

S

=5V,0V

●

100110

180

µA

µA

V

S

=±15V

●

130160

250

µA

µA

ELECTRICALCHARACTERISTICSThe●denotesthespecificationswhichapplyovertheoperating

temperaturerangeof–40°Cto125°CforH-gradeparts,otherwispecificationsareatT

A

=25°enceamplifierconfiguration,

V

S

=5V,0Vor±15V;V

CM

=V

REF

=halfsupply,unlessotherwinoted.

Note1:StressbeyondtholistedunderAbsoluteMaximumRatings

retoanyAbsolute

MaximumRatingconditionforextendedperiodsmayaffectdevice

reliabilityandlifetime.

Note2:TheP3/M3andP9/M9inputsshouldnotbetakenmorethan0.2V

1/M1inputscanwithstand±60VifP9/M9

aregroundedandV

S

=±15V(eApplicationsInformationctionabout

“HighVoltageCMDifferenceAmplifiers”).

Note3:Aheatsinkmayberequiredtokeepthejunctiontemperature

belowabsolutemaximumratings.

Note4:BoththeLT1991CandLT1991Iareguaranteedfunctionaloverthe

–40°Cto85°1991Hisguaranteedfunctional

overthe–40°Cto125°Ctemperaturerange.

Note5:TheLT1991Cisguaranteedtomeetthespecifiedperformance

from0°Cto70°Candisdesigned,characterizedandexpectedtomeet

specifiedperformancefrom–40°Cto85°CbutisnottestedorQAsampled

1991Iisguaranteedtomeetspecified

performancefrom–40°Cto85°1991Hisguaranteedtomeet

specifiedperformancefrom–40°Cto125°C.

Note6:Thisparameterisnot100%tested.

Note7:InputvoltagerangeisguaranteedbytheCMRRtestatV

S

=±15V.

Fortheothervoltages,thisparameterisguaranteedbydesignandthrough

correlationwiththe±ApplicationsInformationctionto

determinethevalidinputvoltagerangeundervariousoperatingconditions.

Note8:Offtvoltage,offtvoltagedriftandPSRRaredefinedas

calculateoutputofftasfollows.

Inthecaofbalancedsourceresistance,V

OS,OUT

=V

OS

•NOISEGAIN

+I

OS

•450k+I

B

•450k•(1–R

P

/R

N

)whereR

P

andR

N

arethetotal

resistanceattheopamppositiveandnegativeterminalrespectively.

Note9:Appliestoresistorsthatareconnectedtotheinvertinginputs.

Resistormatchingisnottesteddirectly,butisguaranteedbythegain

errortest.

Note10:Inputimpedanceistestedbyacombinationofdirect

measurementsandcorrelationtotheCMRRandgainerrortests.

Note11:I

B

andI

OS

aretestedatV

S

=5V,0Vonly.

LT1991

71991fd

SUPPLYVOLTAGE(±V)

0

S

U

P

P

L

Y

C

U

R

R

E

N

T

(

μ

A

)

200

175

150

125

100

75

50

25

0

16

1991G01

426101418

8

12

20

T

A

=85°C

T

A

=–40°C

T

A

=25°C

TEMPERATURE(°C)

–50

O

U

T

P

U

T

V

O

L

T

A

G

E

S

WI

N

G

(

m

V

)

100

1991G02

050

60

40

20

V

EE

–252575125

V

S

=5V,0V

NOLOAD

OUTPUTHIGH

(RIGHTAXIS)

OUTPUTLOW

(LEFTAXIS)

V

CC

–20

–40

–60

LOADCURRENT(mA)

0

O

U

T

P

U

T

V

O

L

T

A

G

E

(

m

V

)

1400

1200

1000

800

600

400

200

V

EE

1991G03

2

1098765

1

34

V

S

=5V,0V

T

A

=85°C

T

A

=–40°C

T

A

=25°C

LOADCURRENT(mA)

V

CC

–100

–200

–300

–400

–500

–600

–700

–800

–900

–1000

O

U

T

P

U

T

V

O

L

T

A

G

E

S

WI

N

G

(

m

V

)

1991G04

0123

4

5

678910

V

S

=5V,0V

T

A

=85°C

T

A

=–40°C

T

A

=25°C

TEMPERATURE(°C)

–50

O

U

T

P

U

T

S

H

O

R

T

-

CI

R

C

UI

T

C

U

R

R

E

N

T

(

m

A

)

25

20

15

10

5

0

0

50

75

1991G05

–25

25

100

125

V

S

=5V,0V

SINKING

SOURCING

GAIN(V/V)

1

I

N

P

U

T

O

F

F

S

E

T

V

O

L

T

A

G

E

(

μ

V

)

150

100

50

0

–50

–100

–150

1291011135

1991G06

238764

V

S

=5V,0V

REPRESENTATIVEPARTS

GAIN(V/V)

1

O

U

T

P

U

T

O

F

F

S

E

T

V

O

L

T

A

G

E

(

μ

V

)

1000

750

500

250

0

–250

–500

–750

–1000

1291011135

1991G07

238764

V

S

=5V,0V

REPRESENTATIVEPARTS

LOADCURRENT(mA)

0

G

AI

N

E

R

R

O

R

(

%)

3

5

1991G08

124

0.04

0.03

0.02

0.01

0

–0.01

–0.02

–0.03

–0.04

GAIN=1

V

S

=±15V

V

OUT

=±10V

T

A

=25°C

REPRESENTATIVEUNITS

TEMPERATURE(°C)

–50

S

L

E

W

R

A

T

E

(

V/

μ

s

)

0.30

0.25

0.20

0.15

0.10

0.05

0

2575

1991G09

–250

50100125

GAIN=1

V

S

=±15V

V

OUT

=±10V

SR

–

(FALLINGEDGE)

SR

+

(RISINGEDGE)

TYPICALPERFORMANCECHARACTERISTICS

SupplyCurrentvsSupplyVoltage

OutputVoltageSwing

vsTemperature

OutputVoltageSwing

vsLoadCurrent(OutputLow)

OutputVoltageSwing

vsLoadCurrent(OutputHigh)

OutputShort-CircuitCurrent

vsTemperature

InputOfftVoltage

vsDifferenceGain

OutputOfftVoltage

vsDifferenceGainGainErrorvsLoadCurrentSlewRatevsTemperature

(DifferenceAmplifierConfiguration)

LT1991

81991fd

GAINSETTING(V/V)

1

–

3

d

B

B

A

N

D

WI

D

T

H

(

k

H

z

)

120

100

80

60

40

20

0

3579

1991G10

2

V

S

=5V,0V

T

A

=25°C

BandwidthvsGainCMRRvsFrequencyPSRRvsFrequency

OutputImpedancevsFrequencyCMRRvsTemperatureGainErrorvsTemperature

GainvsFrequencyGainandPhavsFrequency0.01Hzto1HzVoltageNoi

(DifferenceAmplifierConfiguration)

FREQUENCY(Hz)

C

M

R

R

(

d

B

)

120

110

100

90

80

70

60

50

40

30

20

10

0

101k10k1M

1991G11

100100k

V

S

=5V,0V

T

A

=25°C

GAIN=9

GAIN=1

GAIN=3

P

S

R

R

(

d

B

)

120

110

100

90

80

70

60

50

40

30

20

10

0

V

S

=5V,0V

T

A

=25°C

GAIN=9

GAIN=1

GAIN=3

FREQUENCY(Hz)

101k10k

1991G12

100100k

FREQUENCY(Hz)

O

U

T

P

U

T

I

M

P

E

D

A

N

C

E

(

Ω)

11001k100k10k

1991G13

10

1000

100

10

1

0.1

0.01

V

S

=5V,0V

T

A

=25°C

GAIN=9

GAIN=1

GAIN=3

TEMPERATURE(°C)

–50

C

M

R

R

(

d

B

)

120

100

80

60

40

20

0

2575

1991G14

–250

50100125

GAIN=1

V

S

=±15V

REPRESENTATIVEUNITS

TEMPERATURE(°C)

–50

G

AI

N

E

R

R

O

R

(

%)

0.030

0.025

0.020

0.015

0.010

0.005

0

2575

1991G15

–250

50100125

GAIN=1

V

S

=±15V

REPRESENTATIVEUNITS

FREQUENCY(kHz)

1

G

AI

N

(

d

B

)

30

20

10

0

–10

–20

10100

600

1991G16

GAIN=9

GAIN=3

GAIN=1

V

S

=5V,0V

T

A

=25°C

FREQUENCY(kHz)

1

G

AI

N

(

d

B

)PHASE(deg)

2

1

0

–1

–2

–3

–4

–5

–6

–7

–8

0

–45

–90

–135

–180

10100

400

1991G17

0.5

V

S

=5V,0V

T

A

=25°C

GAIN=1

PHASE

GAIN

V

S

=±15V

T

A

=25°C

MEASUREDING=13

REFERREDTOOPAMPINPUTS

TIME(s)

O

P

A

M

P

V

O

L

T

A

G

E

N

OI

S

E

(

1

0

0

n

V/

DI

V

)

1991G21

TYPICALPERFORMANCECHARACTERISTICS

LT1991

91991fd

TYPICALPERFORMANCECHARACTERISTICS

BLOCKDIAGRAM

PINFUNCTIONS

P1(Pin1):tsa450k

internalresistortotheopamp’snoninvertinginput.

P3(Pin2):tsa150k

internalresistortotheopamp’snoninvertinginput.

P9(Pin3):tsa50k

internalresistortotheopamp’snoninvertinginput.

V

EE

(Pin4):itherground

(insinglesupplyapplications),oranegativevoltage(in

splitsupplyapplications).

REF(Pin5):eoutputlevelwhen

tsa450kinternal

resistortotheopamp’snoninvertinginput.

OUT(Pin6):Output.V

OUT

=V

REF

+1•(V

P1

–V

M1

)+3•

(V

P3

–V

M3

)+9•(V

P9

–V

M9

).

V

CC

(Pin7):nythingfrom

2.7Vto36VabovetheV

EE

voltage.

M9(Pin8):tsa50k

internalresistortotheopamp’sinvertinginput.

M3(Pin9):tsa150k

internalresistortotheopamp’sinvertinginput.

M1(Pin10):tsa450k

internalresistortotheopamp’sinvertinginput.

ExpodPad:MustbesolderedtoPCB.

(DifferenceAmplifierConfiguration)

50mV/DIV

5μs/DIV

GAIN=1

1991G18

50mV/DIV

5μs/DIV1991G19

GAIN=3

50mV/DIV

5μs/DIV

GAIN=9

1991G20

BandwidthvsGainCMRRvsFrequencyPSRRvsFrequency

LT1991

1991BD

98

2345

7610

1

M1M3M9

P1P3P9

V

CC

V

EE

OUT

REF

50k

50k

150k

150k

450k

450k

450k

450k

INM

INP

OUT

4pF

4pF

LT1991

101991fd

Introduction

TheLT1991maybethelastopampyoueverhavetostock.

Becauitprovidesyouwithveralprecisionmatched

resistors,youcaneasilyconfigureitintoveraldifferent

classicalgaincircuitswithoutaddingexternalcomponents.

Theveralpagesofsimplecircuitsinthisdatasheet

beconfiguredintodifferenceamplifiers,aswellasinto

invertingandnoninvertingsingleendedamplifi

factthattheresistorsandopampareprovidedtogether

insuchasmallpackagewilloftensaveyouboardspace

andreducecomplexityforeasyprobing.

TheOpAmp

TheopampinternaltotheLT1991isaprecisiondevice

with15µVtypicalofftvoltageand3nAinputbiascurrent.

Theinputofftcurrentixtremelylow,somatchingthe

sourceresistanceenbytheopampinputswillprovide

mpinputsarenot

rail-to-rail,butextendtowithin1.2VofV

CC

and1Vof

V

EE

.Formanyconfigurationsthough,thechipinputswill

functionrail-to-railbecauofeffectiveattenuationtothe

+putistrulyrail-to-rail,gettingtowithin

nbandwidthproductof

egainsof2ormore,

egains

below2,itisstableintocapacitiveloadsupto100pF.

TheResistors

TheresistorsinternaltotheLT1991areverywellmatched

SiChromebadelementsprotectedwithbarriermetal.

Althoughtheirabsolutetoleranceisfairlypoor(±30%),

theirmatchingistowithin0.04%.Thisallowsthechipto

achieveaCMRRof75dB,andgainerrorswithin0.04%.

Theresistorvaluesare50k,150k,and2of450k,con-

istorshavepower

limitationsof1wattforthe450kresistors,0.3wattforthe

150kresistorsand0.5wattforthe50kresistors;however,

inpractice,powerdissipationwillbelimitedwellbelow

thevaluesbythemaximumvoltageallowedonthe

450kresistorsconnectedtothe

M1andP1inputsareisolatedfromthesubstrate,andcan

ing

ofthepins“P1,”“P3,”“P9,”etc.,isbadontheirrelative

eithas9timestheadmittance,the

voltageappliedtotheP9inputhas9timestheeffectof

thevoltageappliedtotheP1input.

Bandwidth

ThebandwidthoftheLT1991willdependonthegainyou

lect(ormoreaccuratelythenoigainresultingfrom

thegainyoulect).Inthelowestconfigurablegainof1,

the–3dBbandwidthislimitedto450kHz,withpeakingof

ighestconfigurablegains,

bandwidthislimitedto32kHz.

InputNoi

TheLT1991inputnoiisdominatedbytheJohnson

noioftheinternalresistors(√

4kTR).Parallelingall

fourresistorstothe+inputgivesa32.1kΩresistance,for

23nV/√

ivalentnetworkonthe

–inputgivesanother23nV/√

Hz,andtakingtheirRMSsum

givesatotal33nV/√

Hzinputreferrednoifl

noidependsonconfigurationandnoigain.

InputResistance

TheLT1991inputresistancesvarywithconfiguration,but

onceconfiat

resistorsconnectedtotheopamp’s–inputarelooking

intoavirtualground,dback

resistancearoundtheopampdoesnotcontributetoinput

orsconnectedtotheopamp’s+input

arelookingintoahighimpedance,sotheyaddasparal-

lelorriesdependingonhowtheyareconnected,and

mp

+inputitlfprentsaveryhighGΩ

classicalnoninvertingopampconfiguration,theLT1991

prentsthehighinputimpedanceoftheopamp,asis

usualforthenoninvertingca.

CommonModeInputVoltageRange

TheLT1991validcommonmodeinputrangeislimited

bythreefactors:

mallowedvoltageonthepins

utvoltagerangeoftheinternalopamp

utputvoltage

APPLICATIONSINFORMATION

LT1991

111991fd

ThemaximumvoltageallowedontheP3,M3,P9,and

M9inputsincludesthepositiveandnegativesupplyplus

insshouldnotbedrivenmorethan

becautheyare

connectedthroughdiodestointernalmanufacturingpost-

packagetrimcircuitry,andthroughasubstratediodeto

V

EE

.Ifmorethan10mAisallowedtoflowthroughthe

pins,thereisariskthattheLT1991willbedetrimmedor

1andM1inputsdonothaveclampdiodes

orsubstratediodesortrimcircuitryandcanbetakenwell

imumallowedvoltageon

theP1andM1pinsis±60V.

Theinputvoltagerangeoftheinternalopampextends

towithin1.2VofV

CC

and1VofV

EE

.Thevoltageatwhich

theopampinputscommonmodeisdeterminedbythe

voltageattheopamp’s+input,andthisisdeterminedby

thevoltagesonpinsP1,P3,P9andREF(e“Calculating

InputVoltageRange”ction).Thisistrueprovidedthat

theopampisfunctioningandfeedbackismaintainingthe

inputsatthesamevoltage,whichbringsustothethird

requirement.

Forvalidcircuitfunction,theopampoutputmustnotbe

putwillclipiftheinputsignalsareattempt-

usuallyhappensduetotoolargeasignallevel,butitcan

alsooccurwithzeroinputdifferentialandmusttherefore

beincludedasanexampleofacommonmodeproblem.

owstheLT1991configured

asagainof13differenceamplifieronasinglesupply

agreat

circuit,butitdoesnotsupportV

DM

=0Vatanycommon

modebecautheoutputclipsintogroundwhiletrying

toproduce0V

OUT

.Itcanbefixedsimplybydeclaringthe

validinputdifferentialrangenottoextendbelow+4mV,

orbyelevatingtheREFpinabove40mV,orbyproviding

anegativesupply.

CalculatingInputVoltageRange

Figure2showstheLT1991inthegeneralizedcaof

adifferenceamplifier,withtheinputsshortedforthe

uesofR

F

andR

G

are

dictatedbyhowthePinputsandREFpinareconnected.

Bysuperpositionwecanwrite:

V

INT

=V

EXT

•(R

F

/(R

F

+R

G

))+V

REF

•(R

G

/(R

F

+R

G

))

Or,solvingforV

EXT

:

V

EXT

=V

INT

•(1+R

G

/R

F

)–V

REF

•R

G

/R

F

ButvalidV

INT

voltagesarelimitedtoV

CC

–1.2VandV

EE

+1V,so:

MAXV

EXT

=(V

CC

–1.2)•(1+R

G

/R

F

)–V

REF

•R

G

/R

F

and:

MINV

EXT

=(V

EE

+1)•(1+R

G

/R

F

)–V

REF

•R

G

/R

F

Thetwovoltagesreprentthehighandlowextremes

ofthecommonmodeinputrange,iftheotherlimitshave

notalreadybeenexceeded(1and3,above).Inmost

cas,theinvertinginputsM1throughM9canbetaken

furtherthanthetwoextremesbecaudoingthisdoes

ulate

thelimitonthisadditionalrange,at,

–

+

1991F01

50k

150k

450k

50k

150k

450k

450k

450k

REF

5V

V

CM

2.5V

V

DM

0V

–

+

8

7

6

5

4

9

10

1

2

3

LT1991

V

OUT

=13•V

DM

4pF

4pF

–

+

V

REF

R

F

R

F

R

G

R

G

1991F02

V

EXT

V

INT

V

CC

V

EE

enceAmplifierCannotProduce

eaNegative

Supply,orRaiPin5,orProvide4mVofV

DM

atingCMInputVoltageRange

APPLICATIONSINFORMATION

LT1991

121991fd

withV

MORE

=0,theopampoutputisatV

REF

.Fromthe

maxV

EXT

(thehighcmlimit),asV

MORE

goespositive,the

opampoutputwillgomorenegativefromV

REF

bythe

amountV

MORE

•R

F

/R

G

,so:

V

OUT

=V

REF

–V

MORE

•R

F

/R

G

Or:

V

MORE

=(V

REF

–V

OUT

)•R

G

/R

F

ThemostnegativethatV

OUT

cangoisV

EE

+0.04V,so:

MaxV

MORE

=(V

REF

–V

EE

–0.04V)•R

G

/R

F

(shouldbepositive)

Thesituationwherethisfunctionisnegative,andthere-

foreproblematic,whenV

REF

=0andV

EE

=0,hasalready

engthoftheequation

isdemonstratedinthatitprovidesthethreesolutions

suggestedinFigure1:raiV

REF

,lowerV

EE

,orprovide

somenegativeV

MORE

.

Likewi,fromthelowercommonmodeextreme,mak-

ingthenegativeinputmorenegativewillraitheoutput

voltage,limitedbyV

CC

–0.04V.

MINV

MORE

=(V

REF

–V

CC

+0.04V)•R

G

/R

F

(shouldbenegative)

Again,theadditionalinputrangecalculatedhereisonly

availableprovidedtheotherremainingconstraintisnot

violated,themaximumvoltageallowedonthepin.

TheClassicalNoninvertingAmplifier:HighInputZ

Perhapsthemostcommonopampconfigurationisthe

noninvertingamplifi4showsthetextbook

1991is

shownonthebottomconfiguredinaprecisiongainof5.5.

Oneofthebenefitsofthenoninvertingopampconfigura-

LT1991maintainsthisbenefihefinitenumberof

availablefeedbackresistorsintheLT1991,thenumberof

gainconfigurationsisalsofipletelistofsuch

Hi-Zinputnoninvertinggainconfigurationsisshownin

thearealsoreprentedinFigure5in

attheP-sideresistorinputshave

beenconnectedsoastomatchthesourceimpedance

sothatgain

andnoigainareidentical,foroptimalprecision.

–

+

V

REF

R

F

R

F

R

G

R

G

1991F03

V

EXT

MAXORMIN

V

INT

V

MORE

V

CC

V

EE

–

+

R

F

R

G

V

IN

V

IN

V

OUT

V

OUT

V

OUT

=GAIN•V

IN

GAIN=1+R

F

/R

G

–

+

1991F04

50k

150k

450k

50k

150k

450k

450k

450k

8

6

5

9

10

1

2

3

LT1991

CLASSICALNONINVERTINGOPAMPCONFIGURATION.

YOUPROVIDETHERESISTORS.

CLASSICALNONINVERTINGOPAMPCONFIGURATION

IMPLEMENTEDWITHLT1991.R

F

=225k,R

G

=50k,GAIN=5.5.

GAINISACHIEVEDBYGROUNDING,FLOATINGORFEEDINGBACK

THEAVAILABLERESISTORSTOARRIVEATDESIREDR

F

ANDR

G

.

WEPROVIDEYOUWITH<0.1%RESISTORS.

4pF

4pF

atingAdditional

VoltageRangeofInvertingInputs

1991asaClassicalNoninvertingOpAmp

APPLICATIONSINFORMATION

LT1991

131991fd

figuringtheMPinsforSimpleNoninvertingGains.

ThePInputsaredrivenasshownintheexamplesonthe

nextpage.

M9,M3,M1Connection

GainM9M3M1

1OutputOutputOutput

1.077OutputOutputGround

1.1OutputFloatGround

1.25FloatOutputGround

1.273OutputGroundOutput

1.3OutputGroundFloat

1.4OutputGroundGround

2FloatFloatGround

2.5FloatGroundOutput

2.8GroundOutputOutput

3.25GroundOutputFloat

3.5GroundOutputGround

4FloatGroundFloat

5FloatGroundGround

5.5GroundFloatOutput

7GroundGroundOutput

10GroundFloatFloat

11GroundFloatGround

13GroundGroundFloat

14GroundGroundGround

APPLICATIONSINFORMATION

LT1991

141991fd

V

S

–

V

S

–

V

S

+

1991F05

M9

M3

M1

P1

P3

P9

OUT

V

CC

V

OUT

V

IN

V

EE

V

S

+

V

S

–

V

S

+

V

S

–

V

S

+

V

S

–

V

S

+

V

S

–

V

S

+

V

S

–

V

S

+

V

S

–

V

S

+

V

S

–

V

S

+

V

S

–

V

S

+

V

S

–

V

S

+

REF

LT1991

8

9

10

1

2

3

7

6

5

4

M9

M3

M1

P1

P3

P9

OUT

V

CC

V

OUT

V

IN

V

EE

REF

LT1991

8

9

10

1

2

3

7

6

5

4

M9

M3

M1

P1

P3

P9

OUT

V

CC

V

OUT

V

IN

V

EE

REF

LT1991

8

9

10

1

2

3

7

6

5

4

M9

M3

M1

P1

P3

P9

OUT

V

CC

V

OUT

V

EE

REF

LT1991

8

9

10

1

2

3

7

6

5

4

M9

M3

M1

P1

P3

P9

OUT

V

CC

V

OUT

V

IN

V

EE

REF

LT1991

8

9

10

1

2

3

7

6

5

4

M9

M3

M1

P1

P3

P9

V

IN

V

IN

V

IN

OUT

V

CC

V

OUT

V

IN

V

EE

REF

LT1991

8

9

10

1

2

3

7

6

5

4

M9

M3

M1

P1

P3

P9

OUT

V

CC

V

OUT

V

IN

V

EE

REF

LT1991

8

9

10

1

2

3

7

6

5

4

M9

M3

M1

P1

P3

P9

OUT

V

CC

V

OUT

V

IN

V

EE

REF

LT1991

8

9

10

1

2

3

7

6

5

4

M9

M3

M1

P1

P3

P9

OUT

V

CC

V

OUT

V

EE

REF

LT1991

8

9

10

1

2

3

7

6

5

4

M9

M3

M1

P1

P3

P9

OUT

V

CC

V

OUT

V

IN

V

EE

REF

LT1991

8

9

10

1

2

3

7

6

5

4

M9

M3

M1

P1

P3

P9

OUT

V

CC

V

OUT

V

EE

REF

LT1991

8

9

10

1

2

3

7

6

5

4

GAIN=1GAIN=2GAIN=3.25

GAIN=4GAIN=5GAIN=5.5

GAIN=7GAIN=10

GAIN=13GAIN=14

GAIN=11

plementationsofClassicalNoninverting

putZIsMaintained.

APPLICATIONSINFORMATION

LT1991

151991fd

V

IN

OKAYUP

TO±60V

+

50k

150k

450k

450k

5

1

2

3

LT1991ATTENUATINGTOTHE+INPUTBY

DRIVINGANDGROUNDINGANDFLOATING

INPUTSR

A

=450k,R

G

=50k,SOA=0.1.

V

INT

V

INT

V

INT

=A•V

IN

A=R

G

/(R

A

+R

G

)

V

IN

LT1991

R

A

R

G

1991F06

CLASSICALATTENUATOR

4pF

AttenuationUsingthePInputResistors

Attenuationhappensasamatteroffactindifference

amplifierconfigurations,butitisalsoudforreducing

peaksignallevelorimprovinginputcommonmoderange

gnalconditioning

indicatesaneedforattenuation,theLT1991resistorsare

rprecisionresistorscanprovide

veralattenuationlevels,andthearetabulatedin

Table2asadesignreference.

Becautheattenuationsandthenoninvertinggainsaret

independently,ovideshigh

gainresolution,about340uniquegainsbetween0.077

and14,toolargeanumber

totabulate,butthedesignercancalculateachievablegain

bytakingthevectorproductofthegainsandattenuations

inTables1and2,e

gainresolutionis1.5%,withaworst-caof7%.

1991ProvidesforEasyAttenuationtotheOpAmp’s

+1InputCanBeTakenWellOutsideoftheSupplies.

346UniqueGainSettingsAchievablewiththe

LT1991byCombiningAttenuationwithNoninvertingGain

COUNT

0

100

10

1

0.1

0.01

150

1991F07

50100200

250350

300

G

A

I

N

figuringthePPinsforVariousAttenuations.

ThoShowninBoldAreFunctionalEvenWhentheInputDrive

ExceedstheSupplies.

P9,P3,P1,REFConnection

AP9P3P1REF

0.0714GroundGroundDriveGround

0.0769GroundGroundDriveFloat

0.0909GroundFloatDriveGround

0.1GroundFloatDriveFloat

0.143GroundGroundDriveDrive

0.182GroundFloatDriveDrive

0.2FloatGroundDriveGround

0.214GroundDriveGroundGround

0.231GroundDriveFloatGround

0.25FloatGroundDriveFloat

0.286GroundDriveDriveGround

0.308GroundDriveDriveFloat

0.357GroundDriveDriveDrive

0.4FloatGroundDriveDrive

0.5FloatFloatDriveGround

0.6FloatDriveGroundGround

0.643DriveGroundGroundGround

0.692DriveGroundFloatGround

0.714DriveGroundDriveGround

0.75FloatDriveFloatGround

0.769DriveGroundDriveFloat

0.786DriveGroundDriveDrive

0.8FloatDriveDriveGround

0.818DriveFloatGroundGround

0.857DriveDriveGroundGround

0.9DriveFloatFloatGround

0.909DriveFloatDriveGround

0.923DriveDriveFloatGround

0.929DriveDriveDriveGround

1DriveDriveDriveDrive

APPLICATIONSINFORMATION

LT1991

161991fd

InvertingConfiguration

Theinvertingamplifier,showninFigure8,isanother

classicalopampconficuitisactually

identicaltothenoninvertingamplifierofFigure4,except

thatV

IN

tofavail-

ablegainsisshowninTable3,andsomeofthecircuits

ainis1+|Gain|,asisthe

usualcaforinvertingamplifi,forthebestDC

performance,matchthesourceimpedanceenbythe

opampinputs.

–

+

R

F

R

G

V

IN

V

IN

(DRIVE)

V

OUT

V

OUT

V

OUT

=GAIN•V

IN

GAIN=–R

F

/R

G

–

+

1991F08

50k

150k

450k

50k

150k

450k

450k

450k

8

6

5

9

10

1

2

3

LT1991

CLASSICALINVERTINGOPAMPCONFIGURATION.

YOUPROVIDETHERESISTORS.

CLASSICALINVERTINGOPAMPCONFIGURATIONIMPLEMENTED

WITHLT1991.R

F

=225k,R

G

=50k,GAIN=–4.5.

GAINISACHIEVEDBYGROUNDING,FLOATINGORFEEDINGBACK

THEAVAILABLERESISTORSTOARRIVEATDESIREDR

F

ANDR

G

.

WEPROVIDEYOUWITH<0.1%RESISTORS.

4pF

4pF

1991asaClassicalInvertingOpAmp.

NotetheCircuitIsIdenticaltotheNoninvertingAmplifier,

ExceptthatV

IN

andGroundHaveBeenSwapped.

figuringtheMPinsforSimpleInvertingGains

M9,M3,M1Connection

GainM9M3M1

–0.077OutputOutputDrive

–0.1OutputFloatDrive

–0.25FloatOutputDrive

–0.273OutputDriveOutput

–0.3OutputDriveFloat

–0.4OutputDriveDrive

–1FloatFloatDrive

–1.5FloatDriveOutput

–1.8DriveOutputOutput

–2.25DriveOutputFloat

–2.5DriveOutputDrive

–3FloatDriveFloat

–4FloatDriveDrive

–4.5DriveFloatOutput

–6DriveDriveOutput

–9DriveFloatFloat

–10DriveFloatDrive

–12DriveDriveFloat

–13DriveDriveDrive

APPLICATIONSINFORMATION

LT1991

171991fd

4

V

S

–

4

V

S

–

V

S

+

1991F09

M9

M3

M1

P1

P3

P9

OUT

V

CC

V

OUT

V

IN

V

EE

V

S

–

V

S

+

V

S

–

V

S

+

V

S

+

V

S

–

V

S

+

V

S

–

V

S

+

V

S

–

V

S

+

V

S

–

V

S

+

V

S

–

V

S

+

V

S

–

V

S

+

V

S

–

V

S

+

REF

LT1991

8

9

10

1

2

3

7

6

5

M9

M3

M1

P1

P3

P9

OUT

V

CC

V

OUT

V

IN

V

EE

REF

LT1991

8

9

10

1

2

3

7

6

5

4

M9

M3

M1

P1

P3

P9

OUT

V

CC

V

OUT

V

IN

V

EE

REF

LT1991

8

9

10

1

2

3

7

6

5

4

M9

M3

M1

P1

P3

P9

OUT

V

CC

V

OUT

V

EE

REF

LT1991

8

9

10

1

2

3

7

6

5

4

M9

M3

M1

P1

P3

P9

OUT

V

CC

V

OUT

V

IN

V

EE

REF

LT1991

8

9

10

1

2

3

7

6

5

4

M9

M3

M1

P1

P3

P9

V

IN

V

IN

V

IN

OUT

V

CC

V

OUT

V

IN

V

EE

REF

LT1991

8

9

10

1

2

3

7

6

5

4

M9

M3

M1

P1

P3

P9

OUT

V

CC

V

OUT

V

IN

V

EE

REF

LT1991

8

9

10

1

2

3

7

6

5

4

M9

M3

M1

P1

P3

P9

OUT

V

CC

V

OUT

V

IN

V

EE

REF

LT1991

8

9

10

1

2

3

7

6

5

4

M9

M3

M1

P1

P3

P9

OUT

V

CC

V

OUT

V

EE

REF

LT1991

8

9

10

1

2

3

7

6

5

M9

M3

M1

P1

P3

P9

OUT

V

CC

V

OUT

V

IN

V

EE

REF

LT1991

8

9

10

1

2

3

7

6

5

4

M9

M3

M1

P1

P3

P9

OUT

V

CC

V

OUT

V

EE

REF

LT1991

8

9

10

1

2

3

7

6

5

4

GAIN=–0.25GAIN=–1GAIN=–2.25

GAIN=–3GAIN=–4GAIN=–4.5

GAIN=–6GAIN=–9

GAIN=–12GAIN=–13

GAIN=–10

mpletoGetPrecisionInvertingGainswiththeLT1991.

InputImpedanceVariesfrom45kΩ(Gain=–13)to450kΩ(Gain=–1).

APPLICATIONSINFORMATION

LT1991

181991fd

DifferenceAmplifiers

TheresistorsintheLT1991allowittoeasilymakediffer-

enceamplifi10showsthebasic4-resistor

differenceamplifirencegainof

3isshown,butnoticetheeffectoftheadditionaldashed

ectingthe450kresistorsinparal-

lel,,with

somanyresistors,

4showsthedifferencegainsandhowtheyareachieved.

Notethat,asforinvertingamplifiers,thenoigainis1

morethanthesignalgain.

–

+

R

F

R

G

R

G

V

IN

+

V

IN

+

V

IN

–

V

IN

–

V

OUT

V

OUT

V

OUT

=GAIN•(V

IN

+–V

IN

–)

GAIN=R

F

/R

G

–

+

1991F10

50k

150k

450k

50k

150k

450k

450k

450k

8

6

5

9

10

1

2

3

LT1991

CLASSICALDIFFERENCEAMPLIFIERUSINGTHELT1991

CLASSICALDIFFERENCEAMPLIFIERIMPLEMENTED

WITHLT1991.R

F

=450k,R

G

=150k,GAIN=3.

ADDINGTHEDASHEDCONNECTIONSCONNECTSTHE

TWO450kRESISTORSINPARALLEL,SOR

F

ISREDUCED

COMES225k/150k=1.5.

R

F

PARALLEL

TOCHANGE

R

F

,R

G

M9

M3

M1

P1

P3

P9

4pF

4pF

enceAmplifiSet

SimplybyConnectingtheCorrectResistorsorCombinations

3IsShown,withDashedLinesModifying

ainIsOptimal.

tionsGivingDifferenceGainsfortheLT1991

GainV

IN

+V

IN

–OutputGND(REF)

0.077P1M1M3,M9P3,P9

0.1P1M1M9P9

0.25P1M1M3P3

0.273P3M3M1,M9P1,P9

0.3P3M3M9P9

0.4P1,P3M1,M3M9P9

1P1M1

1.5P3M3M1P1

1.8P9M9M1,M3P1,P3

2.25P9M9M3P3

2.5P1,P9M1,M9M3P3

3P3M3

4P1,P3M1,M3

4.5P9M9M1P1

6P3,P9M3,M9M1P1

9P9M9

10P1,P9M1,M9

12P3,P9M3,M9

13P1,P3,P9M1,M3,M9

APPLICATIONSINFORMATION

LT1991

191991fd

fferenceGainsAreAchievableJustbyStrappingthePins

V

S

–

V

S

+

1991F11

M9

M3

M1

P1

P3

P9

OUT

V

CC

V

OUT

V

EE

V

S

–

V

S

+

V

S

–

V

S

+

V

S

–

V

S

+

V

S

–

V

S

+

V

S

–

V

S

+

V

S

–

V

S

+

V

S

–

V

S

+

V

S

–

V

S

+

V

S

–

V

S

+

V

S

–

V

S

+

REF

LT1991

8

9

10

1

2

3

7

6

5

4

M9

M3

M1

P1

P3

P9

OUT

V

CC

V

OUT

V

EE

REF

LT1991

8

9

10

1

2

3

7

6

5

4

M9

M3

M1

P1

P3

P9

OUT

V

CC

V

OUT

V

EE

REF

LT1991

8

9

10

1

2

3

7

6

5

4

M9

M3

M1

P1

P3

P9

OUT

V

CC

V

OUT

V

EE

REF

LT1991

8

9

10

1

2

3

7

6

5

4

M9

M3

M1

P1

P3

P9

OUT

V

CC

V

OUT

V

EE

REF

LT1991

8

9

10

1

2

3

7

6

5

4

M9

M3

M1

P1

P3

P9

OUT

V

CC

V

OUT

V

EE

REF

LT1991

8

9

10

1

2

3

7

6

5

4

M9

M3

M1

P1

P3

P9

OUT

V

CC

V

OUT

V

EE

REF

LT1991

8

9

10

1

2

3

7

6

5

4

M9

M3

M1

P1

P3

P9

OUT

V

CC

V

OUT

V

EE

REF

LT1991

8

9

10

1

2

3

7

6

5

4

M9

M3

M1

P1

P3

P9

OUT

V

CC

V

OUT

V

EE

REF

LT1991

8

9

10

1

2

3

7

6

5

4

M9

M3

M1

P1

P3

P9

OUT

V

CC

V

OUT

V

EE

REF