INA326INA327

SBOS222D – NOVEMBER 2001 – REVISED NOVEMBER 2004

www.ti.com

DESCRIPTIONThe INA326 and INA327 (with shutdown) are high-perfor-mance, low-cost, precision instrumentation amplifiers withrail-to-rail input and output. They are true single-supplyinstrumentation amplifiers with very low DC errors and inputcommon-mode ranges that extends beyond the positive andnegative rails. These features make them suitable for appli-cations ranging from general-purpose to high-accuracy.

Excellent long-term stability and very low 1/f noise assurelow offset voltage and drift throughout the life of the product.

The INA326 (without shutdown) comes in the MSOP-8 pack-age. The INA327 (with shutdown) is offered in an MSOP-10.Both are specified over the industrial temperature range,–40°C to +85°C, with operation from –40°C to +125°C.

FEATURES PRECISION

LOW OFFSET: 100µV (max)LOW OFFSET DRIFT: 0.4µV/°C (max)EXCELLENT LONG-TERM STABILITYVERY-LOW 1/f NOISE

TRUE RAIL-TO-RAIL I/OINPUT COMMON-MODE RANGE:

20mV Below Negative Rail to 100mV AbovePositive Rail

WIDE OUTPUT SWING: Within 10mV of RailsSUPPLY RANGE: Single +2.7V to +5.5V

SMALL SIZEmicroPACKAGE: MSOP-8, MSOP-10

LOW COST

PRODUCTION DATA information is current as of publication date.Products conform to specifications per the terms of Texas Instrumentsstandard warranty. Production processing does not necessarily includetesting of all parameters.

Copyright © 2001-2004, Texas Instruments Incorporated

Precision, Rail-to-Rail I/OINSTRUMENTATION AMPLIFIER

Please be aware that an important notice concerning availability, standard warranty, and use in critical applications ofTexas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.

APPLICATIONS LOW-LEVEL TRANSDUCER AMPLIFIER FOR

BRIDGES, LOAD CELLS, THERMOCOUPLES

WIDE DYNAMIC RANGE SENSORMEASUREMENTS

HIGH-RESOLUTION TEST SYSTEMS

WEIGH SCALES

MULTI-CHANNEL DATA ACQUISITIONSYSTEMS

MEDICAL INSTRUMENTATION

GENERAL-PURPOSE

INA326 AND INA327 RELATED PRODUCTSPRODUCT FEATURES

INA337 Precision, 0.4µV/°C Drift, Specified –40°C to +125°CINA114 50µV VOS, 0.5nA IB, 115dB CMR, 3mA IQ, 0.25µV/°C DriftINA118 50µV VOS, 1nA IB, 120dB CMR, 385µA IQ, 0.5µV/°C DriftINA122 250µV VOS, –10nA IB, 85µA IQ, Rail-to-Rail Output, 3µV/°C DriftINA128 50µV VOS, 2nA IB, 125dB CMR, 750µA IQ, 0.5µV/°C DriftINA321 500µV VOS, 0.5pA IB, 94dB CMRR, 60µA IQ, Rail-to-Rail Output

INA326R1

R2 C2

VIN−

VIN+

7

V+

4

V−

VO

5

6

21

83 G = 2(R2/R1)

INA327INA326

INA326, INA3272SBOS222Dwww.ti.com

SPECIFIEDPACKAGE TEMPERATURE PACKAGE ORDERING TRANSPORT

PRODUCT PACKAGE-LEAD DESIGNATOR RANGE MARKING NUMBER MEDIA, QUANTITY

INA326 MSOP-8 DGK –40°C to +85°C B26 INA326EA/250 Tape and Reel, 250" " " " " INA326EA/2K5 Tape and Reel, 2500

INA327 MSOP-10 DGS –40°C to +85°C B27 INA327EA/250 Tape and Reel, 250" " " " " INA327EA/2K5 Tape and Reel, 2500

NOTE: (1) For the most current package and ordering information, download the latest version of this data sheet and see the Package Option Addendum locatedat the end of the data sheet.

PACKAGE/ORDERING INFORMATION(1)

ABSOLUTE MAXIMUM RATINGS(1)

Supply Voltage .................................................................................. +5.5VSignal Input Terminals: Voltage(2) .............................. –0.5V to (V+) + 0.5V

Current(2) ................................................... ±10mAOutput Short-Circuit ................................................................. ContinuousOperating Temperature Range ....................................... –40°C to +125°CStorage Temperature Range .......................................... –65°C to +150°CJunction Temperature .................................................................... +150°CLead Temperature (soldering, 10s) ............................................... +300°C

NOTES: (1) Stresses above these ratings may cause permanent damage.Exposure to absolute maximum conditions for extended periods may degradedevice reliability. These are stress ratings only, and functional operation of thedevice at these or any other conditions beyond those specified is not implied.(2) Input terminals are diode clamped to the power-supply rails. Input signals thatcan swing more than 0.5V beyond the supply rails should be current limited to10mA or less.

ELECTROSTATICDISCHARGE SENSITIVITY

This integrated circuit can be damaged by ESD. TexasInstruments recommends that all integrated circuits be handledwith appropriate precautions. Failure to observe proper han-dling and installation procedures can cause damage.

ESD damage can range from subtle performance degrada-tion to complete device failure. Precision integrated circuitsmay be more susceptible to damage because very smallparametric changes could cause the device not to meet itspublished specifications.

1

2

3

4

8

7

6

5

R1

V+

VO

R2

R1

VIN−

VIN+

V−

INA326

MSOP- 8

1

2

3

4

5

10

9

8

7

6

R1

V+

VO

R2

Enable

R1

VIN−

VIN+

V−

(Connect to V+)

INA327

MSOP- 10

Top View

PIN CONFIGURATION

INA326, INA327 3SBOS222D www.ti.com

ELECTRICAL CHARACTERISTICS: VS = +2.7V to +5.5VBOLDFACE limits apply over the specified temperature range, TA = –40°C to +85°CAt TA = +25°C, RL = 10kΩ, G = 100 (R1 = 2kΩ, R2 = 100kΩ), external gain set resistors, and IACOMMON = VS /2, with external equivalent filter corner of 1kHz, unlessotherwise noted.

INA326EA, INA327EA

PARAMETER CONDITION MIN TYP MAX UNITS

INPUTOffset Voltage, RTI VOS VS = +5V, VCM = VS /2 ±20 ±100 µV

Over Temperature ±124 µVvs Temperature dVOS/dT ±0.1 ±0.4 µV/°Cvs Power Supply PSR VS = +2.7V to +5.5V, VCM = VS /2 ±20 ±3 µV/VLong-Term Stability See Note (1)

Input Impedance, Differential 1010 || 2 Ω || pFCommon-Mode 1010 || 14 Ω || pF

Input Voltage Range (V–) – 0.02 (V+) + 0.1 VSafe Input Voltage (V–) – 0.5 (V+) + 0.5 VCommon-Mode Rejection CMR VS = +5V, VCM = (V–) – 0.02V to (V+) + 0.1V 100 114 dB

Over Temperature 94 dB

INPUT BIAS CURRENT VCM = VS /2Bias Current IB VS = +5V ±0.2 ±2 nA

vs Temperature See Typical CharacteristicsOffset Current IOS VS = +5V ±0.2 ±2 nA

NOISEVoltage Noise, RTI RS = 0Ω, G = 100, R1 = 2kΩ, R2 = 100kΩ

f = 10Hz 33 nV/√Hzf = 100Hz 33 nV/√Hzf = 1kHz 33 nV/√Hzf = 0.01Hz to 10Hz 0.8 µVp-p

Voltage Noise, RTI RS = 0Ω, G = 10, R1 = 20kΩ, R2 = 100kΩf = 10Hz 120 nV/√Hzf = 100Hz 97 nV/√Hzf = 1kHz 97 nV/√Hzf = 0.01Hz to 10Hz 4 µVp-p

Current Noise, RTIf = 1kHz 0.15 pA/√Hzf = 0.01Hz to 10Hz 4.2 pAp-p

Output Ripple, VO Filtered(2) See Applications Information

GAINGain Equation G = 2(R2/R1)Range of Gain < 0.1 > 10000 V/VGain Error(3) G = 10, 100, VS = +5V, VO = 0.075V to 4.925V ±0.08 ±0.2 %

vs Temperature G = 10, 100, VS = +5V, VO = 0.075V to 4.925V ±6 ±25 ppm/°CNonlinearity G = 10, 100, VS = +5V, VO = 0.075V to 4.925V ±0.004 ±0.01 % of FS

OUTPUTVoltage Output Swing from Rail RL = 100kΩ 5 mV

RL = 10kΩ, VS = +5V 75 10 mVOver Temperature 75 mV

Capacitive Load Drive 500 pFShort-Circuit Current ISC ±25 mA

INTERNAL OSCILLATORFrequency of Auto-Correction 90 kHz

Accuracy ±20 %

FREQUENCY RESPONSEBandwidth(4), –3dB BW G = 1 to 1k 1 kHzSlew Rate(4) SR VS = +5V, All Gains, CL = 100pF Filter LimitedSettling Time(4), 0.1% tS 1kHz Filter, G = 1 to 1k, VO = 2V step, CL = 100pF 0.95 ms

0.01% 1.3 ms0.1% 10kHz Filter, G = 1 to 1k, VO = 2V step, CL = 100pF 130 µs0.01% 160 µs

Overload Recovery(4) 1kHz Filter, 50% Output Overload, G = 1 to 1k 30 µs10kHz Filter, 50% Output Overload, G = 1 to 1k 5 µs

INA326, INA3274SBOS222Dwww.ti.com

PARAMETER CONDITION MIN TYP MAX UNITS

POWER SUPPLYSpecified Voltage Range +2.7 +5.5 VQuiescent Current IQ IO = 0, Diff VIN = 0V, VS = +5V 2.4 3.4 mA

Over Temperature 3.7 mA

SHUTDOWNDisable (Logic Low Threshold) 0.25 VEnable (Logic High Threshold) 1.6 VEnable Time(5) 75 µsDisable Time 100 µsShutdown Current and Enable Pin Current VS = +5V, Disabled 2 5 µA

TEMPERATURE RANGESpecified Range –40 +85 °COperating Range –40 +125 °CStorage Range –65 +150 °CThermal Resistance θJA MSOP-8, MSOP-10 Surface-Mount 150 °C/W

NOTES: (1) 1000-hour life test at 150°C demonstrated randomly distributed variation in the range of measurement limits—approximately 10µV. (2) See ApplicationsInformation section, and Figures 1 and 3. (3) Does not include error and TCR of external gain-setting resistors. (4) Dynamic response is limited by filtering. Higherbandwidths can be achieved by adjusting the filter. (5) See Typical Characteristics, “Input Offset Voltage vs Warm-Up Time”.

ELECTRICAL CHARACTERISTICS: VS = +2.7V to +5.5V (Cont.)BOLDFACE limits apply over the specified temperature range, TA = –40°C to +85°CAt TA = +25°C, RL = 10kΩ, G = 100 (R1 = 2kΩ, R2 = 100kΩ), external gain set resistors, and IACOMMON = VS /2, with external equivalent filter corner of 1kHz, unlessotherwise noted.

INA326EA, INA327EA

INA326, INA327 5SBOS222D www.ti.com

TYPICAL CHARACTERISTICSAt TA = 25°C, VS = +5V, Gain = 100, and RL = 10kΩ with external equivalent filter corner of 1kHz, unless otherwise noted.

GAIN vs FREQUENCY1kHz FILTER

Frequency (Hz)

10 100 1k 10k 100k 1M

Gai

n (d

B)

80

60

40

20

0

−20

−40

G = 1k

G = 100

G = 10

G = 1

GAIN vs FREQUENCY10kHz FILTER

Frequency (Hz)

10 100 1k 10k 100k 1M

Gai

n (d

B)

80

60

40

20

0

−20

−40

G = 1k

G = 100

G = 10

G = 1

COMMON- MODE REJECTION vs FREQUENCY1kHz FILTER

Frequency (Hz)

10 100 1k 10k 100k 1M

CM

R (

dB)

160

140

120

100

80

60

40

20

G = 1k

G = 100

G = 10

G = 1

COMMON- MODE REJECTION vs FREQUENCY10kHz FILTER

Frequency (Hz)

10 100 1k 10k 100k 1M

CM

R (

dB)

160

140

120

100

80

60

40

20

G = 100

G = 10G = 1

G = 1k

POWER- SUPPLY REJECTION vs FREQUENCY

Frequency (Hz)

10 100 1k 10k 100k

PS

R (

dB)

120

100

80

60

40

20

0

G = 100, 1k

G = 10

G = 1

Filter Frequency10kHz1kHz

INPUT- REFERRED VOLTAGE NOISE AND INPUT BIAS CURRENT NOISE vs FREQUENCY

10kHz FILTER

1

10k

1k

100

10

1

0.1

0.01

0.00110 100 1k 10k

Frequency (Hz)

Inpu

t-R

efer

red

Vol

tage

Noi

se (

nV/√

Hz)

Inpu

t Bia

s C

urre

nt N

oise

(pA

/√H

z)G = 1

G = 100

Current Noise(all gains)

G = 10

G = 1000

INA326, INA3276SBOS222Dwww.ti.com

TYPICAL CHARACTERISTICS (Cont.)At TA = 25°C, VS = +5V, Gain = 100, and RL = 10kΩ with external equivalent filter corner of 1kHz, unless otherwise noted.

SMALL- SIGNAL RESPONSEG = 1, 10, AND 100

50m

V/d

iv

500µs/div

1kHz Filter

10kHz Filter

SMALL- SIGNAL STEP RESPONSEG = 1000

50m

V/d

iv

500µs/div

1kHz Filter

LARGE- SIGNAL RESPONSEG = 1 TO 1000

2V/d

iv

500µs/div

1kHz Filter

10kHz Filter

INPUT OFFSET VOLTAGE vs TURN- ON TIME1kHz FILTER, G = 100

Inpu

t Offs

et V

olta

ge (

20µV

/div

)

10 2

Turn- On Time (ms)

FilterSettling

Time

DeviceTurn- On

Time(75µs)

INPUT OFFSET VOLTAGE vs WARM- UP TIME10kHz FILTER, G = 100

Inpu

t Offs

et V

olta

ge (

20µV

/div

)

0.2 0.30 0.1 0.4

Warm- Up Time (ms)

FilterSettling

Time

DeviceTurn- On

Time

0.01Hz TO 10Hz VOLTAGE NOISE

200n

V/d

iv

10s/div

INA326, INA327 7SBOS222D www.ti.com

TYPICAL CHARACTERISTICS (Cont.)At TA = 25°C, VS = +5V, Gain = 100, and RL = 10kΩ with external equivalent filter corner of 1kHz, unless otherwise noted.

OFFSET VOLTAGE DRIFT PRODUCTION DISTRIBUTIONG = 1

Offset Voltage Drift (µV/°C)

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40

Pop

ulat

ion

OFFSET VOLTAGE PRODUCTION DISTRIBUTIONG = 1

Offset Voltage (µV)

−10,

000

−900

0−8

000

−700

0−6

000

−500

0−4

000

−300

0−2

000

−100

0 010

0020

0030

0040

0050

0060

0070

0080

0090

0010

,000

Pop

ulat

ion

OFFSET VOLTAGE DRIFT PRODUCTION DISTRIBUTIONG = 10

Offset Voltage Drift (µV/°C)

00.

20.

40.

60.

81.

01.

21.

41.

61.

82.

02.

22.

42.

62.

83.

03.

23.

43.

63.

84.

0

Pop

ulat

ion

OFFSET VOLTAGE PRODUCTION DISTRIBUTIONG = 10

Offset Voltage (µV)

−100

0−9

00−8

00−7

00−6

00−5

00−4

00−3

00−2

00−1

00 010

020

030

040

050

060

070

080

090

010

00

Pop

ulat

ion

OFFSET VOLTAGE DRIFT PRODUCTION DISTRIBUTIONG = 100, 1000

Offset Voltage Drift (µV/°C)

00.

020.

040.

060.

080.

100.

120.

140.

160.

180.

200.

220.

240.

260.

280.

300.

320.

340.

360.

380.

40

Pop

ulat

ion

OFFSET VOLTAGE PRODUCTION DISTRIBUTIONG = 100, 1000

Offset Voltage (µV)

−100 −9

0−8

0−7

0−6

0−5

0−4

0−3

0−2

0−1

0 0 10 20 30 40 50 60 70 80 90 100

Pop

ulat

ion

INA326, INA3278SBOS222Dwww.ti.com

TYPICAL CHARACTERISTICS (Cont.)At TA = 25°C, VS = +5V, Gain = 100, and RL = 10kΩ with external equivalent filter corner of 1kHz, unless otherwise noted.

INPUT BIAS CURRENT vs TEMPERATURE

Temperature (°C)

−50 −25 0 25 50 75 100 125

I B (

nA)

2.0

1.5

1.0

0.5

0

−0.5

−1.0

−1.5

−2.0

IB+

IB−

QUIESCENT CURRENT vs TEMPERATURE

Temperature (°C)

−50 −25 0 25 50 75 100 125

I Q (

mA

)

3.0

2.5

2.0

1.5

1.0

0.5

0

VS = +2.7V

VS = +5V

GAIN ERROR PRODUCTION DISTRIBUTIONG = 100

Gain Error (m%)

−200

−180

−160

−140

−120

−100 −8

0−6

0−4

0−2

0 0 20 40 60 80 100

120

140

160

180

200

Pop

ulat

ion

INPUT- REFERRED RIPPLE SPECTRUMG = 100

Frequency (Hz)

0 200k 400k 600k 800k 1M

VO

UT (

dBV

)

−100

−110

−120

−130

−140

−150

−160

−170

−180

VO

UT (

µVrm

s)

100.000

31.600

1.000

0.316

0.100

0.030

0.010

0.003

0.001

INA326, INA327 9SBOS222D www.ti.com

IACOMMON(2)

INA326R1

VIN−

VIN+

VO FilteredVO

6

2

1

8

3G = 2(R2/R1)

fO = 1kHz

RO100Ω

CO(1)

1µF

R2 C2(1)

7

+2.5V

4

0.1µF

−2.5V

5

(1) C2 and CO combine to form a 2-pole response that is −3dB at 1kHz. Each individual pole is at 1.5kHz.(2) Output voltage is referenced to IACOMMON (see text).

DESIRED R1 R2 || C2GAIN (Ω) (Ω || nF)

0.1 400k 20k || 50.2 400k 40k || 2.50.5 400k 100k || 11 400k 200k || 0.52 200k 200k || 0.55 80k 200k || 0.510 40k 200k || 0.520 20k 200k || 0.550 8k 200k || 0.5100 4k 200k || 0.5200 2k 200k || 0.5500 2k 500k || 0.2

1000 2k 1M || 0.12000 2k 2M || 0.055000 2k 5M || 0.0210000 2k 10M || 0.01

APPLICATIONS INFORMATIONFigure 1 shows the basic connections required for operation ofthe INA326. A 0.1µF capacitor, placed close to and across thepower-supply pins is strongly recommended for highest accu-racy. RoCo is an output filter that minimizes auto-correctioncircuitry noise. This output filter may also serve as an anti-aliasing filter ahead of an Analog-to-Digital (A/D) converter. Itis also optional based on desired precision.

The output reference terminal is taken at the low side of R2

(IACOMMON).

The INA326 uses a unique internal topology to achieve excel-lent Common-Mode Rejection (CMR). Unlike conventionalinstrumentation amplifiers, CMR is not affected by resistancein the reference connections or sockets. See “Inside theINA326” for further detail. To achieve best high-frequencyCMR, minimize capacitance on pins 1 and 8.

FIGURE 1. Basic Connections. NOTE: Connections for INA327 differ—see Pin Configuration for detail.

SETTING THE GAIN

The INA326 is a 2-stage amplifier with each stage gain setby R1 and R2, respectively (see Figure 5, “Inside the INA326”,for details). Overall gain is described by the equation:

GRR

= 2 2

1(1)

The stability and temperature drift of the external gain-settingresistors will affect gain by an amount that can be directlyinferred from the gain equation (1).

Resistor values for commonly used gains are shown inFigure 1. Gain-set resistor values for best performance aredifferent for +5V single-supply and for ±2.5V dual-supplyoperation. Optimum value for R1 can be calculated by:

R1 = VIN, MAX/12.5µA (2)

where R1 must be no less than 2kΩ.

DESIRED R1 R2 || C2GAIN (Ω) (Ω || nF)

0.1 400k 20k || 50.2 400k 40k || 2.50.5 400k 100k || 11 200k 100k || 12 100k 100k || 15 40k 100k || 110 20k 100k || 120 10k 100k || 150 4k 100k || 1100 2k 100k || 1200 2k 200k || 0.5500 2k 500k || 0.2

1000 2k 1M || 0.12000 2k 2M || 0.055000 2k 5M || 0.0210000 2k 10M || 0.01

NOTES: (1) C2 and CO combine to form a 2-pole response that is –3dB at 1kHz. Each individual pole is at 1.5kHz. (2) Output voltage is referenced toIACOMMON (see text). (3) Output offset voltage required for measurement near zero (see Figure 6).

INA326 VO FilteredVO

6

G = 2(R2/R1)

fO = 1kHz

RO100Ω

CO(1)

1µF

R2 C2(1)

7

V+

4

0.1µF

5

IACOMMON(2)

R1

(1) C2 and CO combine to form a 2-pole response that is −3dB at 1kHz. Each individual pole is at 1.5kHz.(2) Output voltage is referenced to IACOMMON (see text).(3) Output offset voltage required for measurement near zero (see Figure 28).

Single-supply operation may require R2 > 100kΩ for full output swing. This may produce higher input referred offset voltage. See Offset Voltage, Drift, and Circuit Values for detail.

1

8

VIN−

VIN+

2

3(3)

INA326, INA32710SBOS222Dwww.ti.com

Following this design procedure for R1 produces the maximumpossible input stage gain for best accuracy and lowest noise.

Circuit layout and supply bypassing can affect performance.Minimize the stray capacitance on pins 1 and 8. Use recom-mended supply bypassing, including a capacitor directly frompin 7 to pin 4 (V+ to V–), even with dual (split) power supplies(see Figure 1).

OFFSET VOLTAGE, DRIFT, AND CIRCUIT VALUES

As with other multi-stage instrumentation amplifiers, input-referred offset voltage depends on gain and circuit values. Thespecified offset and drift performance is rated at R1 = 2kΩ,R2 = 100kΩ, and VS = ±2.5V. Offset voltage and drift for othercircuit values can be estimated from the following equations:

VOS = 10µV + (50nA)(R2)/G (3)

dVOS/dT = 0.12µV/°C + (0.16nA/°C)(R2)/G (4)

These equations might imply that offset and drift can beminimized by making the value of R2 much lower than thevalues indicated in Figure 1. These values, however, havebeen chosen to assure that the output current into R2 is keptless than or equal to ±25µA, while maintaining R1’s valuegreater than or equal to 2kΩ. Some applications with limitedoutput voltage swing or low power-supply voltage may allowlower values for R2, thus providing lower input-referred offsetvoltage and offset voltage drift.

Conversely, single-supply operation with R2 grounded re-quires that R2 values be made larger to assure that currentremains under 25µA. This will increase the input-referredoffset voltage and offset voltage drift.

Circuit conditions that cause more than 25µA to flow in R2 willnot cause damage, but may produce more nonlinearity.

INA327 ENABLE FUNCTION

The INA327 adds an enable/shutdown function to the INA326.Its pinout differs from the INA326—see the Pin Configurationfor detail.

The INA327 can be enabled by applying a logic HIGHvoltage level to the Enable pin. Conversely, a logic LOWvoltage level will disable the amplifier, reducing its supplycurrent from 2.4mA to typically 2µA. For battery-operatedapplications, this feature may be used to greatly reduce theaverage current and extend battery life. This pin should beconnected to a valid high or low voltage or driven, not leftopen circuit. The Enable pin can be modeled as a CMOSinput gate as in Figure 2.

The enable time following shutdown is 75µs plus the settlingtime due to filters (see Typical Characteristics, “Input OffsetVoltage vs Warm-up Time”). Disable time is 100µs. Thisallows the INA327 to be operated as a “gated” amplifier, orto have its output multiplexed onto a common output bus.When disabled, the output assumes a high-impedance state.

INA327 PIN 5

Pin 5 of the INA327 should be connected to V+ to ensureproper operation.

DYNAMIC PERFORMANCE

The typical characteristic “Gain vs Frequency” shows that theINA326 has nearly constant bandwidth regardless of gain.This results from the bandwidth limiting from the recom-mended filters.

NOISE PERFORMANCE

Internal auto-correction circuitry eliminates virtually all 1/fnoise (noise that increases at low frequency) in gains of 100or greater. Noise performance is affected by gain-settingresistor values. Follow recommendations in the “SettingGain” section for best performance.

Total noise is a combination of input stage noise and outputstage noise. When referred to the input, the total mid-bandnoise is:

V nV HznV Hz

GN = +33800

//

(5)

The output noise has some 1/f components that affectperformance in gains less than 10. See typical characteristic“Input-Referred Voltage Noise vs Frequency.”

High-frequency noise is created by internal auto-correctioncircuitry and is highly dependent on the filter characteristicschosen. This may be the dominant source of noise visiblewhen viewing the output on an oscilloscope. Low cutofffrequency filters will provide lowest noise. Figure 3 shows thetypical noise performance as a function of cutoff frequency.

FIGURE 2. Enable Pin Model.

V+

Enable

6

2µA

FIGURE 3. Total Output Noise vs Required Filter CutoffFrequency.

1001 10 1k 10kRequired Filter Cutoff Frequency (Hz)

Tota

l Out

put N

oise

(µV

RM

S)

1k

100

10

1

G = 10

G = 1

G = 100

G = 1000

INA326, INA327 11SBOS222D www.ti.com

Applications sensitive to the spectral characteristics of high-frequency noise may require consideration of the spuriousfrequencies generated by internal clocking circuitry. “Spurs”occur at approximately 90kHz and its harmonics (see typicalcharacteristic “Input-Referred Ripple Spectrum”) which maybe reduced by additional filtering below 1kHz.

Insufficient filtering at pin 5 can cause nonlinearity with largeoutput voltage swings (very near the supply rails). Noisemust be sufficiently filtered at pin 5 so that noise peaks do not“hit the rail” and change the average value of the signal.Figure 3 shows guidelines for filter cutoff frequency.

HIGH-FREQUENCY NOISE

C2 and CO form filters to reduce internally generated auto-correction circuitry noise. Filter frequencies can be chosen tooptimize the trade-off between noise and frequency re-sponse of the application, as shown in Figure 3. The cutofffrequencies of the filters are generally set to the samefrequency. Figure 3 shows the typical output noise for fourgains as a function of the –3dB cutoff frequency of each filterresponse. Small signals may exhibit the addition of internallygenerated auto-correction circuitry noise at the output. Thisnoise, combined with broadband noise, becomes most evi-dent in higher gains with filters of wider bandwidth.

INPUT BIAS CURRENT RETURN PATH

The input impedance of the INA326 is extremely high—approximately 1010Ω. However, a path must be provided forthe input bias current of both inputs. This input bias current isapproximately ±0.2nA. High input impedance means that thisinput bias current changes very little with varying input voltage.

Input circuitry must provide a path for this input bias currentfor proper operation. Figure 4 shows provision for an inputbias current path in a thermocouple application. Without abias current path, the inputs will float to an undefined poten-tial and the output voltage may not be valid.

INPUT COMMON-MODE RANGE

Common instrumentation amplifiers do not respond linearly withcommon-mode signals near the power-supply rails, even if “rail-to-rail” op amps are used. The INA326 uses a unique topologyto achieve true rail-to-rail input behavior (see Figure 5, “Insidethe INA326”). The linear input voltage range of each inputterminal extends to 20mV below the negative rail, and 100mVabove the positive rail.

INPUT PROTECTION

The inputs of the INA326 are protected with internal diodesconnected to the power-supply rails. These diodes will clampthe applied signal to prevent it from damaging the inputcircuitry. If the input signal voltage can exceed the powersupplies by more than 0.5V, the input signal current shouldbe limited to less than 10mA to protect the internal clampdiodes. This can generally be done with a series inputresistor. Some signal sources are inherently current-limitedand do not require limiting resistors.

FILTERING

Filtering can be adjusted through selection of R2C2 andROCO for the desired trade-off of noise and bandwidth.Adjustment of these components will result in more or lessripple due to auto-correction circuitry noise and will alsoaffect broadband noise. Filtering limits slew rate, settlingtime, and output overload recovery time.

It is generally desirable to keep the resistance of RO relativelylow to avoid DC gain error created by the subsequent stageloading. This may result in relatively high values for CO toproduce the desired filter response. The impedance of ROCO

can be scaled higher to produce smaller capacitor values ifthe load impedance is very high.

Certain capacitor types greater than 0.1µF may have dielec-tric absorption effects that can significantly increase settlingtime in high-accuracy applications (settling to 0.01%). Polypro-pylene, polystyrene, and polycarbonate types are generallygood. Certain “high-K” ceramic types may produce slowsettling “tails.” Settling time to 0.1% is not generally affectedby high-K ceramic capacitors. Electrolytic types are notrecommended for C2 and CO.

INA326Thermocouple5

FIGURE 4. Providing Input Bias Current Return Path.

INA326, INA32712SBOS222Dwww.ti.com

The INA326 uses a new, unique internal circuit topologythat provides true rail-to-rail input. Unlike other instrumen-tation amplifiers, it can linearly process inputs up to 20mVbelow the negative power-supply rail, and 100mV abovethe positive power-supply rail. Conventional instrumenta-tion amplifier circuits cannot deliver such performance,even if rail-to-rail op amps are used.

The ability to reject common-mode signals is derived inmost instrumentation amplifiers through a combination ofamplifier CMR and accurately matched resistor ratios.The INA326 converts the input voltage to a current.Current-mode signal processing provides rejection of com-mon-mode input voltage and power-supply variation with-out accurately matched resistors.

A simplified diagram shows the basic circuit function. Thedifferential input voltage, (VIN+) – (VIN–) is applied acrossR1. The signal-generated current through R1 comes from

A1 and A2’s output stages. A2 combines the current in R1

with a mirrored replica of the current from A1. The result-ing current in A2’s output and associated current mirror istwo times the current in R1. This current flows in (or out)of pin 5 into R2. The resulting gain equation is:

GRR

= 2 2

1

Amplifiers A1, A2, and their associated mirrors are pow-ered from internal charge-pumps that provide voltagesupplies that are beyond the positive and negative supplyrails. As a result, the voltage developed on R2 can actuallyswing 20mV below the negative power-supply rail, and100mV above the positive supply rail. A3 provides abuffered output of the voltage on R2. A3’s input stage isalso operated from the charge-pumped power supplies fortrue rail-to-rail operation.

FIGURE 5. Simplified Circuit Diagram.

INSIDE THE INA326

A1

V+ V−

Current Mirror

Current Mirror

IR1

IR1

IR1 R1

R2 C2

VO

VIN−

VIN+

IR1

2IR1

2IR1 2IR1

2IR1

2IR1

A3A2

IACOMMON

0.1µF

Current Mirror

Current Mirror

7 4

6

5

3

8

1

2

INA326

INA326, INA327 13SBOS222D www.ti.com

FIGURE 6. Generating Output Offset Voltage.

R1

R′2

5

R0

R2 C2

C0VREF

VO

G = 2 (R2 || R′2)/R1

INA326

R2 and R′2 are chosen to create a small output offset voltage (e.g., 100mV).Gain is determined by the parallel combinationof R2 and R′2.

2

1

8

3

6

FIGURE 7. Output Referenced to VREF/2.

2kΩ

200kΩ

200kΩ

VREF

RO100Ω

5

6

2

1

8

3

CO1µF

C2

INA326A/D

Converter

G = 2(200kΩ || 200kΩ)/2kΩ = 100

FIGURE 8. High-Side Current Shunt Measurement.

INA326

+5V

RL

5

2

1

8

3

6

7 RO100Ω

RS

IL

R1

2kΩ

R2 C2

VO

CO1µF

NOTE: Connection pointof V+ will include ( ) or exclude ( ) quiescent current in the measurementas desired. Output offsetrequired for measurements near zero (see Figure 6).

RS must be chosenso that the input voltagedoes not exceed 100mV beyond the rail.

VO = 2(IL × RS)R2

R1

APPLICATION CIRCUITS

INA326, INA32714SBOS222Dwww.ti.com

FIGURE 10. Low-Side –48V Current Shunt Monitor.

INA326

RL

IL

5

4

2

1

8

3

6

7

RI = 2kΩ 0.1µF

OPA336PA

1nF

+5V

76

2

VCC

GND

34

RF = 100kΩ

RSTART100kΩ

RPULL- DOWN200kΩ

VO = 2(IL × RS)

8.45kΩ

ZMM5231BDICT5.1V

ZVN4525G(zetex)

(High- Voltage n- Channel

FET)

RSVS = 0mVto 50mV max

−

+

−48V

NOTE: 0.2% accuracy. Current shunt monitor circuit can be designed for −250V supplywith appropriate selection of high- voltage FET.

RF

RI

FIGURE 11. High-Side +48V Current Shunt Monitor.

INA326

Load

5

7

2

1

8

3

6

4

7

2

3

6

4

RI2kΩ

OPA336PA

1nF

0.1µF

49.9kΩ

75kΩ

165kΩ

VO = 0.1V to 4.9V

8.45kΩ

ZMM5231BDICT5.1V

RSHUNT

VSHUNT = 0mVto 50mV

−

++48V

VCC

GND

(High- Voltage p- Channel FET)

ZVP4525(zetex)

+5V

FIGURE 9. Low-Side Current Shunt Measurement.

INA326

+5V

RL

RS

IL

RO100Ω

5

2

1

8

3

67

C2

CO1µF

2kΩ

VO

R2

R1

NOTE: Connection point of V− will include ( ) orexclude ( ) quiescent current in the measurementas desired. Output offset required for measurements near zero (see Figure 6).

RS must be chosen so thatthe input voltage does notexceed 20mV beyond the rail.

VO = 2(IL × RS)R2

R1

INA326, INA327 15SBOS222D www.ti.com

FIGURE 15. Programmable ±25µA Current Source with HighOutput Resistance.

FIGURE 12. Output Offset Adjustment.

2kΩ

100kΩ1nF

5

VO = VIN (100) + VDAC

VDAC = 0.075Vto 4.925V

INA326

2

1

8

3

6

DAC

+

−

VIN

INA326

45

72

1

8

3

6

RF = 10k

NOTE: Output resistance is typically 800MΩ.Resolution < 5nA. Recommended values of CF = 1nF to 1µF.

+5V

CF

VREF = +2.5V

R1200kΩ

DAC IOUT = ((+VREF) − (VDAC))

R1 ± 50nA

0V < VDAC < +5V

FIGURE 14. Output from Pin 5 to Allow Swing Beyond the Rail.

INA326

+5V

NC(1)

VO

+15V

−15V

OPA277

VD

C2R2

R1

VCM

5

6

72

1

8

34

4

672

3(2)

NOTES: (1) NC denotes No Connection.(2) Typical swing capability −20mV to (+5V + 100mV).

FIGURE 13. Multiplexed Output.

INA327

4

7

96

2

1

10

3

8R1

R3

R5

+5V

Enable

NOTE: (1) R2, R4, and R6 could be a single, shared resistor to save board space.

INA327

4

7

96

2

1

10

3

8

R4(1)

R2(1)

+5V

Enable

INA327

4

7

96

2

1

10

3

8

R6(1)

+5V

Enable

+1.8V to +5V

Logic

VO

1nF

1nF

1nF

INA326, INA32716SBOS222Dwww.ti.com

FIGURE 16. Programmable ±5mA Current Source.

FIGURE 17. ±27V Output at 200mA Amplifier with 100µV Offset.

INA326

45

72

1

8

3

6

IO = ±5mA with 0.1µA stability.

+2.5V

−2.5V

IO

0.1µF

VREF = +2.5V

RI = 200kΩ

10kΩ49.9Ω

DAC

RLIOUT = 2

VREF − VDAC

200kΩ1 +

10kΩ49.9Ω

INA326

4

4

5

7

7

2

1

8

3

2

3

6

6

+5V

−30V

+30V

IB

10nF

2kΩ

1MΩ

RI = 1kΩ

20kΩ

VI

20kΩ

RF = 100kΩ

OPA551

Internal charge pump in the INA326 allows this node to swing 20mV below ground without a negative supply.

Offset of the high- voltage op amp is controlled by the INA326.

VO = –27V

VOS = –100µV at 200mA

G = − = −100V/VRF

RI

NOTES: (1) The OPA551 is a 60V op amp. (2) The INA326 does not require anegative supply to correct for negative VOS values from the high-voltage op amp.(3) Voltage offset contribution of IB (OPA551) is 100pA • 2kΩ = 0.2µV.

INA326, INA327 17SBOS222D www.ti.com

FIGURE 18. Single-Supply PID Temperature Control Loop.

VS

V−

V+

V−

V+

R19

100k

Ω

R20

5k‰

PO

T

R17

5kΩ

PO

T

R2

100k

Ω

RD

IFF

1MΩ

Dif

fere

nti

ato

r T

C:

100m

s to

1s

R1

100k

Ω

C8

0.1µ

F

R25

10kΩ

R22

10kΩR

2310

kΩ

R21

10kΩ

Pro

po

rtio

nal

Err

or

Am

plif

ier

Bia

s G

ener

ato

r

Lo

op

Gai

nA

dju

st

Set

Tem

p

Gai

n =

100

V/V

Inte

gra

tor

TC

: 1s

to

10s

1/4

OPA

4340

1/4

OPA

4340

1/2

OPA

2340

1/4

OPA

4340

1/4

OPA

4340

CIN

T1µ

FR

INT

10M

Ω

R18

10kΩ

R15

200Ω

R16

2kΩ

PO

T

C3

1nF

VB

IAS

VB

IAS

VB

IAS

VS

VS

VB

IAS

Com

mon

Out

put t

oT

EC

Driv

er

Com

mon

+5V

Inpu

t

VB

IAS

VB

IAS

CD

IFF

1µF

Su

mm

ing

Am

plif

ier

INA

326

VO

6

R14

10kΩ

R13

20Ω

R10

1kΩ

C7

22nF

R8

100k

Ω

R9

2kΩ

R7

1kΩ

PO

T

R11

14.3

kΩ

R12

15kΩ RT

HE

RM

10k‰

R6

9.53

kΩ

C5

1nF

R5

20kΩ

R4

20kΩ

C2

470n

F

C6

10µF

RE

F10

04-

2.5

D1 7V+

4

0.1µ

F

V− 5

88 4 1

IN+

IN−

3 2

+

C4

10F

+

1/2

OPA

2340

VS

VS

C1

1nF

VB

IAS

PACKAGE OPTION ADDENDUM

www.ti.com 10-Jun-2014

Addendum-Page 1

PACKAGING INFORMATION

Orderable Device Status(1)

Package Type PackageDrawing

Pins PackageQty

Eco Plan(2)

Lead/Ball Finish(6)

MSL Peak Temp(3)

Op Temp (°C) Device Marking(4/5)

Samples

INA326EA/250 ACTIVE VSSOP DGK 8 250 Green (RoHS& no Sb/Br)

CU NIPDAUAG Level-2-260C-1 YEAR -40 to 85 B26

INA326EA/250G4 ACTIVE VSSOP DGK 8 250 Green (RoHS& no Sb/Br)

CU NIPDAUAG Level-2-260C-1 YEAR -40 to 85 B26

INA326EA/2K5 ACTIVE VSSOP DGK 8 2500 Green (RoHS& no Sb/Br)

CU NIPDAUAG Level-2-260C-1 YEAR -40 to 85 B26

INA326EA/2K5G4 ACTIVE VSSOP DGK 8 2500 Green (RoHS& no Sb/Br)

CU NIPDAUAG Level-2-260C-1 YEAR -40 to 85 B26

INA327EA/250 ACTIVE VSSOP DGS 10 250 Green (RoHS& no Sb/Br)

CU NIPDAUAG Level-2-260C-1 YEAR -40 to 85 B27

INA327EA/250G4 ACTIVE VSSOP DGS 10 250 Green (RoHS& no Sb/Br)

CU NIPDAUAG Level-2-260C-1 YEAR -40 to 85 B27

INA327EA/2K5 ACTIVE VSSOP DGS 10 2500 Green (RoHS& no Sb/Br)

CU NIPDAUAG Level-2-260C-1 YEAR -40 to 85 B27

(1) The marketing status values are defined as follows:ACTIVE: Product device recommended for new designs.LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.PREVIEW: Device has been announced but is not in production. Samples may or may not be available.OBSOLETE: TI has discontinued the production of the device.

(2) Eco Plan - The planned eco-friendly classification: Pb-Free (RoHS), Pb-Free (RoHS Exempt), or Green (RoHS & no Sb/Br) - please check http://www.ti.com/productcontent for the latest availabilityinformation and additional product content details.TBD: The Pb-Free/Green conversion plan has not been defined.Pb-Free (RoHS): TI's terms "Lead-Free" or "Pb-Free" mean semiconductor products that are compatible with the current RoHS requirements for all 6 substances, including the requirement thatlead not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, TI Pb-Free products are suitable for use in specified lead-free processes.Pb-Free (RoHS Exempt): This component has a RoHS exemption for either 1) lead-based flip-chip solder bumps used between the die and package, or 2) lead-based die adhesive used betweenthe die and leadframe. The component is otherwise considered Pb-Free (RoHS compatible) as defined above.Green (RoHS & no Sb/Br): TI defines "Green" to mean Pb-Free (RoHS compatible), and free of Bromine (Br) and Antimony (Sb) based flame retardants (Br or Sb do not exceed 0.1% by weightin homogeneous material)

(3) MSL, Peak Temp. - The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature.

(4) There may be additional marking, which relates to the logo, the lot trace code information, or the environmental category on the device.

PACKAGE OPTION ADDENDUM

www.ti.com 10-Jun-2014

Addendum-Page 2

(5) Multiple Device Markings will be inside parentheses. Only one Device Marking contained in parentheses and separated by a "~" will appear on a device. If a line is indented then it is a continuationof the previous line and the two combined represent the entire Device Marking for that device.

(6) Lead/Ball Finish - Orderable Devices may have multiple material finish options. Finish options are separated by a vertical ruled line. Lead/Ball Finish values may wrap to two lines if the finishvalue exceeds the maximum column width.

Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is provided. TI bases its knowledge and belief on informationprovided by third parties, and makes no representation or warranty as to the accuracy of such information. Efforts are underway to better integrate information from third parties. TI has taken andcontinues to take reasonable steps to provide representative and accurate information but may not have conducted destructive testing or chemical analysis on incoming materials and chemicals.TI and TI suppliers consider certain information to be proprietary, and thus CAS numbers and other limited information may not be available for release.

In no event shall TI's liability arising out of such information exceed the total purchase price of the TI part(s) at issue in this document sold by TI to Customer on an annual basis.

TAPE AND REEL INFORMATION

*All dimensions are nominal

Device PackageType

PackageDrawing

Pins SPQ ReelDiameter

(mm)

ReelWidth

W1 (mm)

A0(mm)

B0(mm)

K0(mm)

P1(mm)

W(mm)

Pin1Quadrant

INA326EA/250 VSSOP DGK 8 250 330.0 12.4 5.3 3.4 1.4 8.0 12.0 Q1

INA326EA/2K5 VSSOP DGK 8 2500 330.0 12.4 5.3 3.4 1.4 8.0 12.0 Q1

INA327EA/250 VSSOP DGS 10 250 180.0 12.4 5.3 3.4 1.4 8.0 12.0 Q1

INA327EA/2K5 VSSOP DGS 10 2500 330.0 12.4 5.3 3.4 1.4 8.0 12.0 Q1

PACKAGE MATERIALS INFORMATION

www.ti.com 26-Jan-2013

Pack Materials-Page 1

*All dimensions are nominal

Device Package Type Package Drawing Pins SPQ Length (mm) Width (mm) Height (mm)

INA326EA/250 VSSOP DGK 8 250 366.0 364.0 50.0

INA326EA/2K5 VSSOP DGK 8 2500 366.0 364.0 50.0

INA327EA/250 VSSOP DGS 10 250 210.0 185.0 35.0

INA327EA/2K5 VSSOP DGS 10 2500 367.0 367.0 35.0

PACKAGE MATERIALS INFORMATION

www.ti.com 26-Jan-2013

Pack Materials-Page 2

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