INA326
INA327
SBOS222D – NOVEMBER 2001 – REVISED NOVEMBER 2004
www.ti.com
DESCRIPTION
The INA326 and INA327 (with shutdown) are high-perfor-
mance, low-cost, precision instrumentation amplifiers with
rail-to-rail input and output. They are true single-supply
instrumentation amplifiers with very low DC errors and input
common-mode ranges that extends beyond the positive and
negative 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 assure
low 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 STABILITY
VERY-LOW 1/f NOISE
●TRUE RAIL-TO-RAIL I/O
INPUT COMMON-MODE RANGE:
20mV Below Negative Rail to 100mV Above
Positive Rail
WIDE OUTPUT SWING: Within 10mV of Rails
SUPPLY RANGE: Single +2.7V to +5.5V
●SMALL SIZE
micro
PACKAGE: MSOP-8, MSOP-10
●LOW COST
PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of Texas Instruments
standard warranty. Production processing does not necessarily include
testing of all parameters.
Copyright © 2001-2004, Texas Instruments Incorporated
Precision, Rail-to-Rail I/O
INSTRUMENTATION AMPLIFIER
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of
Texas 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 SENSOR
MEASUREMENTS
●HIGH-RESOLUTION TEST SYSTEMS
●WEIGH SCALES
●MULTI-CHANNEL DATA ACQUISITION
SYSTEMS
●MEDICAL INSTRUMENTATION
●GENERAL-PURPOSE
INA326 AND INA327 RELATED PRODUCTS
PRODUCT FEATURES
INA337 Precision, 0.4µV/°C Drift, Specified –40°C to +125°C
INA114 50µV VOS, 0. 5nA I B, 115dB CMR, 3mA I Q, 0.25µV/°C D rift
INA118 50µV VOS, 1 nA IB, 120dB CMR, 38 5µA IQ, 0.5µV/°C D rift
INA122 250µV VOS, –10nA IB, 85µA IQ, Rail-to-Rail Output, 3µV/°C D rift
INA128 50µV VOS, 2 nA IB, 125dB CMR, 75 0µA IQ, 0.5µV/°C Drift
INA321 500µV VOS, 0. 5pA IB, 94dB CMRR, 60µA IQ, Rail-to-Rail Output
INA326R1
R2C2
VIN−
VIN+
7
V+
4
V−
VO
5
6
2
1
8
3G = 2(R2/R1)
INA327
INA326
INA326, INA327
2SBOS222D
www.ti.com
SPECIFIED
PACKAGE 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 located
at the end of the data sheet.
PACKAGE/ORDERING INFORMATION(1)
ABSOLUTE MAXIMUM RATINGS(1)
Supply Voltage.................................................................................. +5.5V
Signal Input Terminals: Voltage(2) ..............................–0.5V to (V+) + 0.5V
Current(2) ................................................... ±10mA
Output Short-Circuit ................................................................. Continuous
Operating Temperature Range ....................................... –40°C to +125°C
Storage Temperature Range .......................................... –65°C to +150°C
Junction Temperature .................................................................... +150°C
Lead Temperature (soldering, 10s) ............................................... +300°C
NOTES: (1) Stresses above these ratings may cause permanent damage.
Exposure to absolute maximum conditions for extended periods may degrade
device reliability. These are stress ratings only, and functional operation of the
device 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 that
can swing more than 0.5V beyond the supply rails should be current limited to
10mA or less.
ELECTROSTATIC
DISCHARGE SENSITIVITY
This integrated circuit can be damaged by ESD. Texas
Instruments recommends that all integrated circuits be handled
with 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 circuits
may be more susceptible to damage because very small
parametric changes could cause the device not to meet its
published specifications.
1
2
3
4
8
7
6
5
R
1
V+
V
O
R
2
R
1
V
IN−
V
IN+
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 3
SBOS222D www.ti.com
ELECTRICAL CHARACTERISTICS: VS = +2.7V to +5.5V
BOLDFACE limits apply over the specified temperature range, TA = –40°C to +85°C
At 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, unless
otherwise noted.
INA326EA, INA327EA
PARAMETER CONDITION MIN TYP MAX UNITS
INPUT
Offset Voltage, RTI VOS VS = +5V, VCM = VS/2 ±20 ±100 µV
Over Temperature ±124 µV
vs Temperature dVOS/dT ±0.1 ±0.4 µV/°C
vs Power Supply PSR VS = +2.7V to +5.5V, VCM = VS/2 ±20 ±3µV/V
Long-Term Stability See Note (1)
Input Impedance, Differential 1010 || 2 Ω || pF
Common-Mode 1010 || 14 Ω || pF
Input Voltage Range (V–) – 0.02 (V+) + 0.1 V
Safe Input Voltage (V–) – 0.5 (V+) + 0.5 V
Common-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/2
Bias Current IBVS = +5V ±0.2 ±2nA
vs Temperature See Typical Characteristics
Offset Current IOS VS = +5V ±0.2 ±2nA
NOISE
Voltage Noise, RTI RS = 0Ω, G = 100, R1 = 2kΩ, R2 = 100kΩ
f = 10Hz 33 nV/
√Hz
f = 100Hz 33 nV/
√Hz
f = 1kHz 33 nV/
√Hz
f = 0.01Hz to 10Hz 0.8 µVp-p
Voltage Noise, RTI RS = 0Ω, G = 10, R1 = 20kΩ, R2 = 100kΩ
f = 10Hz 120 nV/
√Hz
f = 100Hz 97 nV/
√Hz
f = 1kHz 97 nV/
√Hz
f = 0.01Hz to 10Hz 4µVp-p
Current Noise, RTI
f = 1kHz 0.15 pA/
√Hz
f = 0.01Hz to 10Hz 4.2 pAp-p
Output Ripple, VO Filtered(2) See Applications Information
GAIN
Gain Equation G = 2(R2/R1)
Range of Gain < 0.1 > 10000 V/V
Gain 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/°C
Nonlinearity G = 10, 100, VS = +5V, VO = 0.075V to 4.925V ±0.004 ±0.01 % of FS
OUTPUT
Voltage Output Swing from Rail RL = 100kΩ5mV
RL = 10kΩ, VS = +5V 75 10 mV
Over Temperature 75 mV
Capacitive Load Drive 500 pF
Short-Circuit Current ISC ±25 mA
INTERNAL OSCILLATOR
Frequency of Auto-Correction 90 kHz
Accuracy ±20 %
FREQUENCY RESPONSE
Bandwidth(4), –3dB BW G = 1 to 1k 1 kHz
Slew Rate(4) SR VS = +5V, All Gains, CL = 100pF Filter Limited
Settling Time(4), 0.1% tS
1kHz Filter, G = 1 to 1k, VO = 2V step, CL = 100pF
0.95 ms
0.01% 1.3 ms
0.1%
10kHz Filter, G = 1 to 1k, VO = 2V step, CL = 100pF
130 µs
0.01% 160 µs
Overload Recovery(4)
1kHz Filter,
50% Output Overload, G = 1 to 1k 30 µs
10kHz Filter,
50% Output Overload, G = 1 to 1k 5 µs
INA326, INA327
4SBOS222D
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PARAMETER CONDITION MIN TYP MAX UNITS
POWER SUPPLY
Specified Voltage Range +2.7 +5.5 V
Quiescent Current IQIO = 0, Diff VIN = 0V, VS = +5V 2.4 3.4 mA
Over Temperature 3.7 mA
SHUTDOWN
Disable (Logic Low Threshold) 0.25 V
Enable (Logic High Threshold) 1.6 V
Enable Time(5) 75 µs
Disable Time 100 µs
Shutdown Current and Enable Pin Current
VS = +5V, Disabled 2 5 µA
TEMPERATURE RANGE
Specified Range –40 +85 °C
Operating Range –40 +125 °C
Storage Range –65 +150 °C
Thermal Resistance
θ
JA
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 Applications
Information 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. Higher
bandwidths 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°C
At 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, unless
otherwise noted.
INA326EA, INA327EA
INA326, INA327 5
SBOS222D www.ti.com
TYPICAL CHARACTERISTICS
At TA = 25°C, VS = +5V, Gain = 100, and RL = 10kΩ with external equivalent filter corner of 1kHz, unless otherwise noted.
GAIN vs FREQUENCY
1kHz FILTER
Frequency (Hz)
10 100 1k 10k 100k 1M
Gain (dB)
80
60
40
20
0
−20
−40
G = 1k
G = 100
G = 10
G = 1
GAIN vs FREQUENCY
10kHz FILTER
Frequency (Hz)
10 100 1k 10k 100k 1M
Gain (dB)
80
60
40
20
0
−20
−40
G = 1k
G = 100
G = 10
G = 1
COMMON- MODE REJECTION vs FREQUENCY
1kHz FILTER
Frequency (Hz)
10 100 1k 10k 100k 1M
CMR (dB)
160
140
120
100
80
60
40
20
G = 1k
G = 100
G = 10
G = 1
COMMON- MODE REJECTION vs FREQUENCY
10kHz FILTER
Frequency (Hz)
10 100 1k 10k 100k 1M
CMR (dB)
160
140
120
100
80
60
40
20
G = 100
G = 10
G = 1
G = 1k
POWER- SUPPLY REJECTION vs FREQUENCY
Frequency (Hz)
10 100 1k 10k 100k
PSR (dB)
120
100
80
60
40
20
0
G = 100, 1k
G = 10
G = 1
Filter Frequency
10kHz
1kHz
INPUT- REFERRED VOLTAGE NOISE AND
INPUT BIAS CURRENT NOISE vs FREQUENCY
10kHz FILTER
1
10k
1k
100
10
1
0.1
0.01
0.001
10 100 1k 10k
Frequency (Hz)
Input-Referred Voltage Noise (nV/√Hz)
Input Bias Current Noise (pA/√Hz)
G = 1
G = 100
Current Noise
(all gains)
G = 10
G = 1000
INA326, INA327
6SBOS222D
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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 RESPONSE
G = 1, 10, AND 100
50mV/div
500µs/div
1kHz Filter
10kHz Filter
SMALL- SIGNAL STEP RESPONSE
G = 1000
50mV/div
500µs/div
1kHz Filter
LARGE- SIGNAL RESPONSE
G = 1 TO 1000
2V/div
500µs/div
1kHz Filter
10kHz Filter
INPUT OFFSET VOLTAGE vs TURN- ON TIME
1kHz FILTER, G = 100
Input Offset Voltage (20µV/div)
102
Turn- On Time (ms)
Filter
Settling
Time
Device
Turn- On
Time
(75µs)
INPUT OFFSET VOLTAGE vs WARM- UP TIME
10kHz FILTER, G = 100
Input Offset Voltage (20µV/div)
0.2 0.30 0.1 0.4
Warm- Up Time (ms)
Filter
Settling
Time
Device
Turn- On
Time
0.01Hz TO 10Hz VOLTAGE NOISE
200nV/div
10s/div
INA326, INA327 7
SBOS222D 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 DISTRIBUTION
G = 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
Population
OFFSET VOLTAGE PRODUCTION DISTRIBUTION
G = 1
Offset Voltage (µV)
−10,000
−9000
−8000
−7000
−6000
−5000
−4000
−3000
−2000
−1000
0
1000
2000
3000
4000
5000
6000
7000
8000
9000
10,000
Population
OFFSET VOLTAGE DRIFT PRODUCTION DISTRIBUTION
G = 10
Offset Voltage Drift (µV/°C)
0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
2.2
2.4
2.6
2.8
3.0
3.2
3.4
3.6
3.8
4.0
Population
OFFSET VOLTAGE PRODUCTION DISTRIBUTION
G = 10
Offset Voltage (µV)
−1000
−900
−800
−700
−600
−500
−400
−300
−200
−100
0
100
200
300
400
500
600
700
800
900
1000
Population
OFFSET VOLTAGE DRIFT PRODUCTION DISTRIBUTION
G = 100, 1000
Offset Voltage Drift (µV/°C)
0
0.02
0.04
0.06
0.08
0.10
0.12
0.14
0.16
0.18
0.20
0.22
0.24
0.26
0.28
0.30
0.32
0.34
0.36
0.38
0.40
Population
OFFSET VOLTAGE PRODUCTION DISTRIBUTION
G = 100, 1000
Offset Voltage (µV)
−100
−90
−80
−70
−60
−50
−40
−30
−20
−10
0
10
20
30
40
50
60
70
80
90
100
Population
INA326, INA327
8SBOS222D
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.
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
I
B+
I
B−
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
V
S
= +2.7V
V
S
= +5V
GAIN ERROR PRODUCTION DISTRIBUTION
G = 100
Gain Error (m%)
−200
−180
−160
−140
−120
−100
−80
−60
−40
−20
0
20
40
60
80
100
120
140
160
180
200
Population
INPUT- REFERRED RIPPLE SPECTRUM
G = 100
Frequency (Hz)
0 200k 400k 600k 800k 1M
V
OUT
(dBV)
−100
−110
−120
−130
−140
−150
−160
−170
−180
V
OUT
(µVrms)
100.000
31.600
1.000
0.316
0.100
0.030
0.010
0.003
0.001
INA326, INA327 9
SBOS222D www.ti.com
IACOMMON(2)
INA326R1
VIN−
VIN+
VO Filtered
VO
6
2
1
8
3G = 2(R2/R1)
fO = 1kHz
RO
100Ω
CO(1)
1µF
R2C2(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 R1R2|| C2
GAIN (Ω)(Ω|| nF)
0.1 400k 20k || 5
0.2 400k 40k || 2.5
0.5 400k 100k || 1
1 400k 200k || 0.5
2 200k 200k || 0.5
5 80k 200k || 0.5
10 40k 200k || 0.5
20 20k 200k || 0.5
50 8k 200k || 0.5
100 4k 200k || 0.5
200 2k 200k || 0.5
500 2k 500k || 0.2
1000 2k 1M || 0.1
2000 2k 2M || 0.05
5000 2k 5M || 0.02
10000 2k 10M || 0.01
APPLICATIONS INFORMATION
Figure 1 shows the basic connections required for operation of
the INA326. A 0.1µF capacitor, placed close to and across the
power-supply pins is strongly recommended for highest accu-
racy. RoCo is an output filter that minimizes auto-correction
circuitry noise. This output filter may also serve as an anti-
aliasing filter ahead of an Analog-to-Digital (A/D) converter. It
is 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 conventional
instrumentation amplifiers, CMR is not affected by resistance
in the reference connections or sockets. See “Inside the
INA326” for further detail. To achieve best high-frequency
CMR, 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 set
by R1 and R2, respectively (see Figure 5, “Inside the INA326”,
for details). Overall gain is described by the equation:
GR
R
=22
1
(1)
The stability and temperature drift of the external gain-setting
resistors will affect gain by an amount that can be directly
inferred from the gain equation (1).
Resistor values for commonly used gains are shown in
Figure 1. Gain-set resistor values for best performance are
different for +5V single-supply and for ±2.5V dual-supply
operation. Optimum value for R1 can be calculated by:
R1 = VIN, MAX/12.5µA (2)
where R1 must be no less than 2kΩ.
DESIRED R1R2|| C2
GAIN (Ω)(Ω|| nF)
0.1 400k 20k || 5
0.2 400k 40k || 2.5
0.5 400k 100k || 1
1 200k 100k || 1
2 100k 100k || 1
5 40k 100k || 1
10 20k 100k || 1
20 10k 100k || 1
50 4k 100k || 1
100 2k 100k || 1
200 2k 200k || 0.5
500 2k 500k || 0.2
1000 2k 1M || 0.1
2000 2k 2M || 0.05
5000 2k 5M || 0.02
10000 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 to
IACOMMON (see text). (3) Output offset voltage required for measurement near zero (see Figure 6).
INA326 V
O
Filtered
V
O
6
G = 2(R
2
/R
1
)
f
O
= 1kHz
R
O
100Ω
C
O(1)
1µF
R
2
C
2(1)
7
V+
4
0.1µF
5
IA
COMMON(2)
R
1
(1) C
2
and C
O
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 IA
COMMON
(see text).
(3) Output offset voltage required for measurement near zero (see Figure 28).
Single-supply operation may require
R
2
> 100kΩ for full output swing.
This may produce higher input referred
offset voltage. See
Offset Voltage,
Drift, and Circuit Values
for detail.
1
8
V
IN−
V
IN+
2
3
(3)
INA326, INA327
10 SBOS222D
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Following this design procedure for R1 produces the maximum
possible 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 from
pin 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. The
specified offset and drift performance is rated at R1 = 2kΩ,
R2 = 100kΩ, and VS = ±2.5V. Offset voltage and drift for other
circuit 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 be
minimized by making the value of R
2
much lower than the
values indicated in Figure 1. These values, however, have
been chosen to assure that the output current into R
2
is kept
less than or equal to ±25µA, while maintaining R
1
’s value
greater than or equal to 2kΩ. Some applications with limited
output voltage swing or low power-supply voltage may allow
lower values for R
2
, thus providing lower input-referred offset
voltage and offset voltage drift.
Conversely, single-supply operation with R2 grounded re-
quires that R2 values be made larger to assure that current
remains under 25µA. This will increase the input-referred
offset voltage and offset voltage drift.
Circuit conditions that cause more than 25µA to flow in R2 will
not 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 Configuration
for detail.
The INA327 can be enabled by applying a logic HIGH
voltage level to the Enable pin. Conversely, a logic LOW
voltage level will disable the amplifier, reducing its supply
current from 2.4mA to typically 2µA. For battery-operated
applications, this feature may be used to greatly reduce the
average current and extend battery life. This pin should be
connected to a valid high or low voltage or driven, not left
open circuit. The Enable pin can be modeled as a CMOS
input gate as in Figure 2.
The enable time following shutdown is 75µs plus the settling
time due to filters (see Typical Characteristics, “Input Offset
Voltage vs Warm-up Time”). Disable time is 100µs. This
allows the INA327 to be operated as a “gated” amplifier, or
to 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 ensure
proper operation.
DYNAMIC PERFORMANCE
The typical characteristic “Gain vs Frequency” shows that the
INA326 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/f
noise (noise that increases at low frequency) in gains of 100
or greater. Noise performance is affected by gain-setting
resistor values. Follow recommendations in the “Setting
Gain” section for best performance.
Total noise is a combination of input stage noise and output
stage noise. When referred to the input, the total mid-band
noise is:
VnVHznV Hz
G
N=+33 800
//
(5)
The output noise has some 1/f components that affect
performance in gains less than 10. See typical characteristic
“Input-Referred Voltage Noise vs Frequency.”
High-frequency noise is created by internal auto-correction
circuitry and is highly dependent on the filter characteristics
chosen. This may be the dominant source of noise visible
when viewing the output on an oscilloscope. Low cutoff
frequency filters will provide lowest noise. Figure 3 shows the
typical 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 Cutoff
Frequency.
100110 1k10k
Required Filter Cutoff Frequency (Hz)
Total Output Noise (µVRMS)
1k
100
10
1
G = 10
G = 1
G = 100
G = 1000
INA326, INA327 11
SBOS222D www.ti.com
Applications sensitive to the spectral characteristics of high-
frequency noise may require consideration of the spurious
frequencies generated by internal clocking circuitry. “Spurs”
occur at approximately 90kHz and its harmonics (see typical
characteristic “Input-Referred Ripple Spectrum”) which may
be reduced by additional filtering below 1kHz.
Insufficient filtering at pin 5 can cause nonlinearity with large
output voltage swings (very near the supply rails). Noise
must 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 to
optimize the trade-off between noise and frequency re-
sponse of the application, as shown in Figure 3. The cutoff
frequencies of the filters are generally set to the same
frequency. Figure 3 shows the typical output noise for four
gains as a function of the –3dB cutoff frequency of each filter
response. Small signals may exhibit the addition of internally
generated auto-correction circuitry noise at the output. This
noise, 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 for
the input bias current of both inputs. This input bias current is
approximately ±0.2nA. High input impedance means that this
input bias current changes very little with varying input voltage.
Input circuitry must provide a path for this input bias current
for proper operation. Figure 4 shows provision for an input
bias current path in a thermocouple application. Without a
bias 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 with
common-mode signals near the power-supply rails, even if “rail-
to-rail” op amps are used. The INA326 uses a unique topology
to achieve true rail-to-rail input behavior (see Figure 5, “Inside
the INA326”). The linear input voltage range of each input
terminal extends to 20mV below the negative rail, and 100mV
above the positive rail.
INPUT PROTECTION
The inputs of the INA326 are protected with internal diodes
connected to the power-supply rails. These diodes will clamp
the applied signal to prevent it from damaging the input
circuitry. If the input signal voltage can exceed the power
supplies by more than 0.5V, the input signal current should
be limited to less than 10mA to protect the internal clamp
diodes. This can generally be done with a series input
resistor. Some signal sources are inherently current-limited
and do not require limiting resistors.
FILTERING
Filtering can be adjusted through selection of R2C2 and
ROCO for the desired trade-off of noise and bandwidth.
Adjustment of these components will result in more or less
ripple due to auto-correction circuitry noise and will also
affect broadband noise. Filtering limits slew rate, settling
time, and output overload recovery time.
It is generally desirable to keep the resistance of RO relatively
low to avoid DC gain error created by the subsequent stage
loading. This may result in relatively high values for CO to
produce the desired filter response. The impedance of ROCO
can be scaled higher to produce smaller capacitor values if
the load impedance is very high.
Certain capacitor types greater than 0.1µF may have dielec-
tric absorption effects that can significantly increase settling
time in high-accuracy applications (settling to 0.01%). Polypro-
pylene, polystyrene, and polycarbonate types are generally
good. Certain “high-K” ceramic types may produce slow
settling “tails.” Settling time to 0.1% is not generally affected
by high-K ceramic capacitors. Electrolytic types are not
recommended for C2 and CO.
INA326
Thermocouple 5
FIGURE 4. Providing Input Bias Current Return Path.
INA326, INA327
12 SBOS222D
www.ti.com
The INA326 uses a new, unique internal circuit topology
that provides true rail-to-rail input. Unlike other instrumen-
tation amplifiers, it can linearly process inputs up to 20mV
below the negative power-supply rail, and 100mV above
the 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 in
most instrumentation amplifiers through a combination of
amplifier 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. The
differential input voltage, (VIN+) – (VIN–) is applied across
R1. 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 is
two times the current in R1. This current flows in (or out)
of pin 5 into R2. The resulting gain equation is:
GR
R
=22
1
Amplifiers A1, A2, and their associated mirrors are pow-
ered from internal charge-pumps that provide voltage
supplies that are beyond the positive and negative supply
rails. As a result, the voltage developed on R2 can actually
swing 20mV
below
the negative power-supply rail, and
100mV
above
the positive supply rail. A3 provides a
buffered output of the voltage on R2. A3’s input stage is
also operated from the charge-pumped power supplies for
true rail-to-rail operation.
FIGURE 5. Simplified Circuit Diagram.
INSIDE THE INA326
A1
V+ V−
Current Mirror
Current Mirror
I
R1
I
R1
I
R1
R
1
R
2
C
2
V
O
V
IN−
V
IN+
I
R1
2I
R1
2I
R1
2I
R1
2I
R1
2I
R1
A3
A2
IA
COMMON
0.1µF
Current Mirror
Current Mirror
74
6
5
3
8
1
2INA326
INA326, INA327 13
SBOS222D www.ti.com
FIGURE 6. Generating Output Offset Voltage.
R
1
R′
2
5
R
0
R
2
C
2
C
0
V
REF
V
O
G = 2 (R
2
|| R′
2
)/R
1
INA326
R
2
and R′
2
are chosen to
create a small output offset
voltage (e.g., 100mV).
Gain is determined by
the parallel combination
of R
2
and R′
2
.
2
1
8
3
6
FIGURE 7. Output Referenced to VREF/2.
2kΩ
200kΩ
200kΩ
V
REF
R
O
100Ω
5
6
2
1
8
3
C
O
1µF
C
2
INA326 A/D
Converter
G = 2(200kΩ || 200kΩ)/2kΩ = 100
FIGURE 8. High-Side Current Shunt Measurement.
INA326
+5V
RL
5
2
1
8
3
6
7RO
100Ω
RS
IL
R1
2kΩ
R2C2
VO
CO
1µF
NOTE: Connection point
of V+ will include ( ) or
exclude ( ) quiescent
current in the measurement
as desired. Output offset
required for measurements
near zero (see Figure 6).
RS must be chosen
so that the input voltage
does not exceed 100mV
beyond the rail.
VO = 2(IL × RS)R2
R1
APPLICATION CIRCUITS
INA326, INA327
14 SBOS222D
www.ti.com
FIGURE 10. Low-Side –48V Current Shunt Monitor.
INA326
RL
IL
5
4
2
1
8
3
6
7
RI = 2kΩ0.1µF
OPA336PA
1nF
+5V
76
2
VCC
GND
34
RF = 100kΩ
RSTART
100kΩRPULL- DOWN
200kΩ
VO = 2(IL × RS)
8.45kΩ
ZMM5231BDICT
5.1V
ZVN4525G
(zetex)
(High- Voltage
n- Channel
FET)
RS
VS
=
0mV
to 50mV max
−
+
−48V
NOTE: 0.2% accuracy. Current shunt
monitor circuit can be designed for −250V supply
with 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
R
I
2kΩ
OPA336PA
1nF
0.1µF
49.9kΩ
75kΩ
165kΩ
V
O
= 0.1V to 4.9V
8.45kΩ
ZMM5231BDICT
5.1V
R
SHUNT
V
SHUNT
= 0mV
to 50mV
−
+
+48V
V
CC
GND
(High- Voltage
p- Channel FET)
ZVP4525
(zetex)
+5V
FIGURE 9. Low-Side Current Shunt Measurement.
INA326
+5V
RL
RS
IL
RO
100Ω
5
2
1
8
3
6
7
C2
CO
1µF
2kΩ
VO
R2
R1
NOTE: Connection point of V− will include ( ) or
exclude ( ) quiescent current in the measurement
as desired. Output offset required for measurements
near zero (see Figure 6).
RS must be chosen so that
the input voltage does not
exceed 20mV beyond the rail.
VO = 2(IL × RS)R2
R1
INA326, INA327 15
SBOS222D www.ti.com
FIGURE 15. Programmable ±25µA Current Source with High
Output Resistance.
FIGURE 12. Output Offset Adjustment.
2kΩ
100kΩ1nF
5
V
O
= V
IN
(100) + V
DAC
V
DAC
= 0.075V
to 4.925V
INA326
2
1
8
3
6
DAC
+
−
V
IN
INA326
45
7
2
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
R1
200kΩ
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
C2
R2
R1
VCM
5
6
7
2
1
8
34
4
6
7
2
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
8
R
1
R
3
R
5
+5V
Enable
NOTE: (1) R
2
, R
4
, and R
6
could be a
single, shared resistor to save board space.
INA327
4
7
96
2
1
10
3
8
R
4(1)
R
2(1)
+5V
Enable
INA327
4
7
96
2
1
10
3
8
R
6(1)
+5V
Enable
+1.8V to +5V
Logic
V
O
1nF
1nF
1nF
INA326, INA327
16 SBOS222D
www.ti.com
FIGURE 16. Programmable ±5mA Current Source.
FIGURE 17. ±27V Output at 200mA Amplifier with 100µV Offset.
INA326
45
7
2
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
RL
IOUT = 2 VREF − VDAC
200kΩ1 + 10kΩ
49.9Ω
INA326
4
4
5
7
7
2
1
8
3
2
3
6
6
+5V
−30V
+30V
I
B
10nF
2kΩ
1MΩ
R
I
= 1kΩ
20kΩ
V
I
20kΩ
R
F
= 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.
V
O
= –27V
V
OS
= –100µV at 200mA
G = −= −100V/V
R
F
R
I
NOTES: (1) The OPA551 is a 60V op amp. (2) The INA326 does not require a
negative supply to correct for negative V
OS
values from the high-voltage op amp.
(3) Voltage offset contribution of I
B
(OPA551) is 100pA • 2kΩ = 0.2µV.
INA326, INA327 17
SBOS222D www.ti.com
FIGURE 18. Single-Supply PID Temperature Control Loop.
VS
V−
V+
V−
V+
R19
100kΩ
R20
5k‰
POT
R17
5kΩ
POT
R2
100kΩ
RDIFF
1MΩ
Differentiator
TC: 100ms to 1s
R1
100kΩ
C8
0.1µF
R25
10kΩ
R22
10kΩ
R23
10kΩ
R21
10kΩ
Proportional
Error Amplifier
Bias Generator
Loop Gain
Adjust
Set Temp
Gain = 100V/V
Integrator
TC: 1s to 10s
1/4
OPA4340
1/4
OPA4340 1/2
OPA2340
1/4
OPA4340
1/4
OPA4340
CINT
1µF
RINT
10MΩ
R18
10kΩ
R15
200Ω
R16
2kΩ
POT
C3
1nF
VBIAS
VBIAS
VBIAS
VS
VS
VBIAS
Common
Output to
TEC
Driver
Common
+5V Input
VBIAS
VBIAS
CDIFF
1µF
Summing Amplifier
INA326 VO
6
R14
10kΩ
R13
20ΩR10
1kΩ
C7
22nF
R8
100kΩ
R9
2kΩ
R7
1kΩ
POT
R11
14.3kΩ
R12
15kΩ
RTHERM
10k‰
R6
9.53kΩ
C5
1nF
R5
20kΩ
R4
20kΩ
C2
470nF
C6
10µFREF1004- 2.5
D1
7
V+
4
0.1µFV−
5
8
8
4
1
IN+
IN−
3
2
+
C4
10 F
+
1/2
OPA2340
VS
VS
C1
1nF
VBIAS
PACKAGE OPTION ADDENDUM
www.ti.com 16-Aug-2012
Addendum-Page 1
PACKAGING INFORMATION
Orderable Device Status (1) Package Type Package
Drawing Pins Package Qty Eco Plan (2) Lead/
Ball Finish MSL Peak Temp (3) Samples
(Requires Login)
INA326EA/250 ACTIVE VSSOP DGK 8 250 Green (RoHS
& no Sb/Br) CU NIPDAUAGLevel-2-260C-1 YEAR
INA326EA/250G4 ACTIVE VSSOP DGK 8 250 Green (RoHS
& no Sb/Br) CU NIPDAUAGLevel-2-260C-1 YEAR
INA326EA/2K5 ACTIVE VSSOP DGK 8 2500 Green (RoHS
& no Sb/Br) CU NIPDAUAGLevel-2-260C-1 YEAR
INA326EA/2K5G4 ACTIVE VSSOP DGK 8 2500 Green (RoHS
& no Sb/Br) CU NIPDAUAGLevel-2-260C-1 YEAR
INA327EA/250 ACTIVE MSOP DGS 10 250 Green (RoHS
& no Sb/Br) CU NIPDAUAGLevel-2-260C-1 YEAR
INA327EA/250G4 ACTIVE MSOP DGS 10 250 Green (RoHS
& no Sb/Br) CU NIPDAUAGLevel-2-260C-1 YEAR
INA327EA/2K5 ACTIVE MSOP DGS 10 2500 Green (RoHS
& no Sb/Br) CU NIPDAUAGLevel-2-260C-1 YEAR
INA327EA/2K5G4 ACTIVE MSOP DGS 10 2500 Green (RoHS
& no Sb/Br) CU NIPDAUAGLevel-2-260C-1 YEAR
(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 availability
information 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 that
lead 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 between
the 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 weight
in homogeneous material)
(3) MSL, Peak Temp. -- The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature.
PACKAGE OPTION ADDENDUM
www.ti.com 16-Aug-2012
Addendum-Page 2
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 information
provided 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 and
continues 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 Package
Type Package
Drawing Pins SPQ Reel
Diameter
(mm)
Reel
Width
W1 (mm)
A0
(mm) B0
(mm) K0
(mm) P1
(mm) W
(mm) Pin1
Quadrant
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 MSOP DGS 10 250 180.0 12.4 5.3 3.4 1.4 8.0 12.0 Q1
INA327EA/2K5 MSOP DGS 10 2500 330.0 12.4 5.3 3.4 1.4 8.0 12.0 Q1
PACKAGE MATERIALS INFORMATION
www.ti.com 16-Aug-2012
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 MSOP DGS 10 250 210.0 185.0 35.0
INA327EA/2K5 MSOP DGS 10 2500 367.0 367.0 35.0
PACKAGE MATERIALS INFORMATION
www.ti.com 16-Aug-2012
Pack Materials-Page 2
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