©1996 Burr-Brown Corporation PDS-1365C Printed in U.S.A. September, 1997
®
INA126
INA2126
International Airport Industrial Park • Mailing Address: PO Box 11400, Tucson, AZ 85734 • Street Address: 6730 S. Tucson Blvd., Tucson, AZ 85706 • Tel: (520) 746-1111 • Twx: 910-952-1111
Internet: http://www.burr-brown.com/ • FAXLine: (800) 548-6133 (US/Canada Only) • Cable: BBRCORP • Telex: 066-6491 • FAX: (520) 889-1510 • Immediate Product Info: (800) 548-6132
Micro
POWER INSTRUMENTATION AMPLIFIER
Single and Dual Versions
FEATURES
●LOW QUIESCENT CURRENT: 175µA/chan.
●WIDE SUPPLY RANGE: ±1.35V to ±18V
●LOW OFFSET VOLTAGE: 250µV max
●LOW OFFSET DRIFT: 3µV/°C max
●LOW NOISE: 35nV/√Hz
●LOW INPUT BIAS CURRENT: 25nA max
●8-PIN DIP, SO-8, MSOP-8 SURFACE- MOUNT
DUAL: 16-Pin DIP, SO-16, SSOP-16
DESCRIPTION
The INA126 and INA2126 are precision instrumentation
amplifiers for accurate, low noise differential signal acquisi-
tion. Their two-op-amp design provides excellent perfor-
mance with very low quiescent current (175µA/chan.). This,
combined with wide operating voltage range of ±1.35V to
±18V, makes them ideal for portable instrumentation and data
acquisition systems.
Gain can be set from 5V/V to 10000V/V with a single
external resistor. Laser trimmed input circuitry provides
low offset voltage (250µV max), low offset voltage drift
(3µV/°C max) and excellent common-mode rejection.
Single version package options include 8-pin plastic DIP,
SO-8 surface mount, and fine-pitch MSOP-8 surface-mount.
Dual version is available in the space-saving SSOP-16 fine-
pitch surface mount, SO-16, and 16-pin DIP. All are speci-
fied for the –40°C to +85°C industrial temperature range.
APPLICATIONS
●INDUSTRIAL SENSOR AMPLIFIER:
Bridge, RTD, Thermocouple
●PHYSIOLOGICAL AMPLIFIER:
ECG, EEG, EMG
●MULTI-CHANNEL DATA ACQUISITION
●PORTABLE, BATTERY OPERATED SYSTEMS
40kΩ
10kΩ
10kΩ
40kΩ
INA126
5
4
2
1
8
3
7
6
R
G
V
IN
–
V
IN
+
V+
V–
V
O
= (V
IN
– V
IN
) G
–+
80k
R
G
G = 5 +
INA126
INA2126
INA2126
INA126
INA2126
40kΩ
10kΩ
10kΩ
40kΩ
INA2126
5
7
8
1
3
4
29
6
RG
VIN
–
VIN
+
V+
V–
VO = (VIN – VIN) G
–
+
80k
RG
G = 5 +
VO = (VIN – VIN) G
–
+
80k
RG
G = 5 +
40kΩ
10kΩ
10kΩ
40kΩ12
16
14
13
15 11
10
RG
VIN
–
VIN
+
2
®
INA126, INA2126
SPECIFICATIONS
At TA = +25°C, VS = ±15V, RL = 25kΩ, unless otherwise noted.
INA126P, U, E INA126PA, UA, EA
INA2126P, U, E INA2126PA, UA, EA
PARAMETER CONDITIONS MIN TYP MAX MIN TYP MAX UNITS
INPUT
Offset Voltage, RTI ±100 ±250 ±150 ±500 µV
vs Temperature ±0.5 ±3✻±5µV/°C
vs Power Supply (PSRR) VS = ±1.35V to ±18V 5 15 ✻50 µV/V
Input Impedance 109 || 4 ✻Ω || pF
Safe Input Voltage RS = 0 (V–)–0.5 (V+)+0.5 ✻✻V
R
S
= 1kΩ(V–)–10 (V+)+10 ✻✻V
Common-Mode Voltage Range VO = 0V ±11.25 ±11.5 ✻✻ V
Channel Separation (dual) G = 5, dc 130 dB
Common-Mode Rejection RS = 0, VCM = ±11.25V 83 94 74 90 dB
INA2126U (dual SO-16) 80 94 dB
INPUT BIAS CURRENT –10 –25 ✻–50 nA
vs Temperature ±30 ✻pA/°C
Offset Current ±0.5 ±2✻±5nA
vs Temperature ±10 ✻pA/°C
GAIN G = 5 to 10k ✻V/V
Gain Equation G = 5 + 80kΩ/RG✻V/V
Gain Error VO = ±14V, G = 5 ±0.02 ±0.1 ✻±0.18 %
vs Temperature G = 5 ±2±10 ✻✻ppm/°C
Gain Error VO = ±12V, G = 100 ±0.2 ±0.5 ✻±1%
vs Temperature G = 100 ±25 ±100 ✻✻ppm/°C
Nonlinearity G = 100, VO = ±14V ±0.002 ±0.012 ✻✻ %
NOISE
Voltage Noise, f = 1kHz 35 ✻nV/√Hz
f = 100Hz 35 ✻nV/√Hz
f = 10Hz 45 ✻nV/√Hz
fB = 0.1Hz to 10Hz 0.7 ✻µVp-p
Current Noise, f = 1kHz 60 ✻fA/√Hz
fB = 0.1Hz to 10Hz 2 ✻pAp-p
OUTPUT
Voltage, Positive RL = 25kΩ(V+)–0.9 (V+)–0.75 ✻✻ V
Negative RL = 25kΩ(V–)+0.95 (V–)+0.8 ✻✻ V
Short-Circuit Current Short-Circuit to Ground +10/–5 ✻mA
Capacitive Load Drive 1000 ✻pF
FREQUENCY RESPONSE
Bandwidth, –3dB G = 5 200 ✻kHz
G = 100 9 ✻kHz
G = 500 1.8 ✻kHz
Slew Rate VO = ±10V, G = 5 0.4 ✻V/µs
Settling Time, 0.01% 10V Step, G = 5 30 ✻µs
10V Step, G = 100 160 ✻µs
10V Step, G = 500 1500 ✻µs
Overload Recovery 50% Input Overload 4 ✻µs
POWER SUPPLY
Voltage Range ±1.35 ±15 ±18 ✻✻✻ V
Current (per channel) IO = 0 ±175 ±200 ✻✻ µA
TEMPERATURE RANGE
Specification Range –40 +85 ✻✻°C
Operation Range –55 +125 ✻✻°C
Storage Range –55 +125 ✻✻°C
Thermal Resistance,
θ
JA
8-Pin DIP 100 ✻°C/W
SO-8 Surface-Mount 150 ✻°C/W
MSOP-8 Surface-Mount 200 ✻°C/W
16-Pin DIP (dual) 80 ✻°C/W
SO-16 (dual) 100 ✻°C/W
SSOP-16 (dual) 100 ✻°C/W
✻ Specification same as INA126P, INA126U, INA126E; INA2126P, INA2126U, INA2126E.
The information provided herein is believed to be reliable; however, BURR-BROWN assumes no responsibility for inaccuracies or omissions. BURR-BROWN assumes
no responsibility for the use of this information, and all use of such information shall be entirely at the user’s own risk. Prices and specifications are subject to change
without notice. No patent rights or licenses to any of the circuits described herein are implied or granted to any third party. BURR-BROWN does not authorize or warrant
any BURR-BROWN product for use in life support devices and/or systems.
3
®
INA126, INA2126
PIN CONFIGURATION (Single)
Top View 8-Pin DIP, SO-8, MSOP-8
PACKAGE INFORMATION
PACKAGE DRAWING TRANSPORT
PRODUCT PACKAGE NUMBER(1) PACKAGE MARKING ORDERING NUMBER MEDIA
Single
INA126PA 8-Pin DIP 006 INA126PA INA126PA Rails
INA126P 8-Pin DIP 006 INA126P INA126P Rails
INA126UA SO-8 182 INA126UA INA126UA Rails or Reel
INA126U SO-8 182 INA126U INA126U Rails or Reel
INA126EA(2) MSOP-8 337 A26(3) INA126EA-250 Reel Only
" " " " INA126EA-2500 "
INA126E(2) MSOP-8 337 A26(3) INA126E-250 Reel Only
" " " " INA126E-2500 "
Dual
INA2126PA 16-Pin DIP 180 INA2126PA INA2126PA Rails
INA2126P 16-Pin DIP 180 INA2126P INA2126P Rails
INA2126UA SO-16 265 INA2126UA INA2126UA Rails
INA2126U SO-16 265 INA2126U INA2126U Rails
INA2126EA(2) SSOP-16 322 INA2126EA INA2126EA-250 Reel Only
" " " " INA2126EA-2500 "
INA2126E(2) SSOP-16 322 INA2126E INA2126E-250 Reel Only
" " " " INA2126E-2500 "
NOTES: (1) For detailed drawing and dimension table, see end of data sheet, or Appendix C of Burr-Brown IC Data Book. (2) MSOP-8 and SSOP-16 packages are
available only on 250 or 2500 piece reels. (3) Grade designation is marked on reel.
R
G
V
–IN
V
+IN
V–
R
G
V+
V
O
Ref
1
2
3
4
8
7
6
5
PIN CONFIGURATION (Dual)
Top View 16-Pin DIP, SO-16, SSOP-16
V
INA
V
INA
R
GA
R
GA
V
INB
V
INB
R
GB
R
GB
1
2
3
4
Ref
A
V
OA
Sense
A
V–
5
6
7
8
16
15
14
13
Ref
B
V
OB
Sense
B
V+
12
11
10
9
–
+
–
+
Power Supply Voltage, V+ to V– ........................................................36V
Input Signal Voltage(2) ........................................... (V–)–0.7 to (V+)+0.7V
Input Signal Current(2) ...................................................................... 10mA
Output Short Circuit ................................................................. Continuous
Operating Temperature ................................................. –55°C to +125°C
Storage Temperature..................................................... –55°C to +125°C
Lead Temperature (soldering, 10s) ............................................... +300°C
NOTES: (1) Stresses above these ratings may cause permanent damage.
(2) Input signal voltage is limited by internal diodes connected to power
supplies. See text.
ABSOLUTE MAXIMUM RATINGS(1)
ELECTROSTATIC
DISCHARGE SENSITIVITY
This integrated circuit can be damaged by ESD. Burr-Brown
recommends that all integrated circuits be handled with ap-
propriate precautions. Failure to observe proper handling and
installation procedures can cause damage.
ESD damage can range from subtle performance degradation
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.
4
®
INA126, INA2126
TYPICAL PERFORMANCE CURVES
At TA = +25°C and VS = ±15V, unless otherwise noted.
GAIN vs FREQUENCY
70
60
50
40
30
20
10
0
–10
Gain (dB)
Frequency (Hz)
100 1k 10k 100k 1M
G = 1000
G = 100
G = 20
G = 5
COMMON-MODE REJECTION vs FREQUENCY
110
100
90
80
70
60
50
40
30
20
10
0
Common-Mode Rejection (dB)
Frequency (Hz)
10 100 1k 10k 100k 1M
G = 1000
G = 100
G = 5
POSITIVE POWER SUPPLY REJECTION
vs FREQUENCY
120
100
80
60
40
20
0
Power Supply Rejection (dB)
Frequency (Hz)
10 100 1k 10k 100k 1M
G = 1000
G = 100
G = 5
NEGATIVE POWER SUPPLY REJECTION
vs FREQUENCY
120
100
80
60
40
20
0
Power Supply Rejection (dB)
Frequency (Hz)
10 100 1k 10k 100k 1M
G = 1000
G = 100
G = 5
INPUT COMMON-MODE RANGE
vs OUTPUT VOLTAGE, V
S
= ±15V
Output Voltage (V)
Common-Mode Voltage (V)
–15 –10 0 5 15–5
15
10
5
0
–5
–10
–15 10
V
D/2
+
+
–
–
V
CM
V
O
V
D/2
Ref
–15V
+15V
+
Limited by A
2
output swing—see text
Limited by A
2
output swing—see text
INPUT COMMON-MODE VOLTAGE RANGE
vs OUTPUT VOLTAGE, VS = ±5V
Output Voltage (V)
Input Common-Mode Voltage (V)
–5 –4 5–3 –2 –1 0 1 2 3 4
5
4
3
2
1
0
–1
–2
–3
–4
–5
Limited by A
2
output swing—see text
Limited by A
2
output swing—see text
VS = ±5V VS = +5V/0V
VREF = 2.5V
5
®
INA126, INA2126
TYPICAL PERFORMANCE CURVES (CONT)
At TA = +25°C and VS = ±15V, unless otherwise noted.
SETTLING TIME vs GAIN
Gain (V/V)
Settling Time (µs)
1000
100
10 1 10 100 1k
0.01%
0.1%
INPUT-REFERRED OFFSET VOLTAGE WARM-UP
Time After Turn-On (ms)
Offset Voltage Change (µV)
01 1023456789
10
8
6
4
2
0
–2
–4
–6
–8
–10
(Noise)
TOTAL HARMONIC DISTORTION+NOISE
vs FREQUENCY
Frequency (Hz)
THD+N (%)
10 100 1k
1
0.1
0.01
0.001 10k
R
L
= 100kΩ
G = 5
R
L
= 10kΩ
OUTPUT VOLTAGE SWING
vs OUTPUT CURRENT
012345
Output Current (mA)
Output Voltage (V)
Sourcing Current
Sinking Current
V+
(V+)–1
(V+)–2
(V–)+2
(V–)+1
V–
INPUT-REFERRED NOISE vs FREQUENCY
100
10
1
1k
100
10
Input Voltage Noise (nV/√Hz)
Frequency (Hz)
1 10 100 10k1k
Input Current Noise (fA/√Hz)
Voltage Noise
Current Noise
QUIESCENT CURRENT AND SLEW RATE
vs TEMPERATURE
Temperature (°C)
Quiescent Current (µA)
Slew Rate (V/µs)
300
250
200
150
100
50
0
0.6
0.5
0.4
0.3
0.2
0.1
0
–75 –50 –25 0 25 50 75 100 125
+SR
–SR
V
S
= ±5V
V
S
= ±1.35V
I
Q
6
®
INA126, INA2126
TYPICAL PERFORMANCE CURVES (CONT)
At TA = +25°C and VS = ±15V, unless otherwise noted.
20mV/div
20mV/div
50µs/div
50µs/div
5V/div
0.2µV/div
500ms/div
50µs/div
VOLTAGE NOISE, 0.1Hz to 10HzLARGE-SIGNAL RESPONSE, G = 5
SMALL-SIGNAL RESPONSE, G = 5 SMALL-SIGNAL RESPONSE, G = 100
CHANNEL SEPARATION vs FREQUENCY, RTI
(Dual Version)
160
150
140
130
120
110
100
90
80
70
60
Separation (dB)
Frequency (Hz)
100 1k 10k 100k 1M
G = 1000
G = 100
G = 5
Measurement limited
by amplifier or
measurement noise.
R
L
= 25kΩ
7
®
INA126, INA2126
APPLICATION INFORMATION
Figure 1 shows the basic connections required for operation
of the INA126. Applications with noisy or high impedance
power supplies may require decoupling capacitors close to
the device pins as shown.
The output is referred to the output reference (Ref) terminal
which is normally grounded. This must be a low-impedance
connection to ensure good common-mode rejection. A resis-
tance of 8Ω in series with the Ref pin will cause a typical
device to degrade to approximately 80dB CMR.
Dual versions (INA2126) have feedback sense connections,
SenseA and SenseB. These must be connected to their respec-
tive output terminals for proper operation. The sense con-
nection can be used to sense the output voltage directly at the
load for best accuracy.
SETTING THE GAIN
Gain is set by connecting an external resistor, RG, as shown:
(1)
Commonly used gains and RG resistor values are shown in
Figure 1.
The 80kΩ term in equation 1 comes from the internal metal film
resistors which are laser trimmed to accurate absolute values.
The accuracy and temperature coefficient of these resistors are
included in the gain accuracy and drift specifications.
The stability and temperature drift of the external gain
setting resistor, RG, also affects gain. RG’s contribution to
gain accuracy and drift can be directly inferred from the gain
equation (1). Low resistor values required for high gain can
make wiring resistance important. Sockets add to the wiring
resistance, which will contribute additional gain error in
gains of approximately 100 or greater.
OFFSET TRIMMING
The INA126 and INA2126 are laser trimmed for low offset
voltage and offset voltage drift. Most applications require no
external offset adjustment. Figure 2 shows an optional cir-
cuit for trimming the output offset voltage. The voltage
applied to the Ref terminal is added to the output signal. An
op amp buffer is used to provide low impedance at the Ref
terminal to preserve good common-mode rejection.
FIGURE 1. Basic Connections.
DESIRED GAIN RGNEAREST 1%
(V/V) (Ω)R
G VALUE
5NCNC
10 16k 15.8k
20 5333 5360
50 1779 1780
100 842 845
200 410 412
500 162 162
1000 80.4 80.6
2000 40.1 40.2
5000 16.0 15.8
10000 8.0 7.87
NC: No Connection.
G=5+80kΩ
R
G
FIGURE 2. Optional Trimming of Output Offset Voltage.
10kΩ
OPA237
±10mV
Adjustment Range
100Ω
100Ω
100µA
1/2 REF200
100µA
1/2 REF200
V+
V–
R
G
INA126
Ref
V
O
✻
V
IN
–
V
IN
+
✻ Dual version has
external sense connection.
40kΩ
10kΩ
10kΩ
40kΩ
INA126
5
4
2
1
8
3
7
6
RG
RG
VIN
A2
A1
–
VIN
+
VIN
–
VIN
+
V+
V–
INA126
0.1µF
0.1µF
VO
VO
Ref
✻
Ref
Load
+
–
Also drawn in simplified form:
VO = (VIN – VIN) G
–+
80k
RG
G = 5 +
✻
Pin numbers are
for single version
✻ Dual version has
external sense connection.
8
®
INA126, INA2126
INPUT BIAS CURRENT RETURN
The input impedance of the INA126/2126 is extremely
high—approximately 109Ω. However, a path must be pro-
vided for the input bias current of both inputs. This input
bias current is typically –10nA (current flows out of the
input terminals). 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 3 shows various provisions for
an input bias current path. Without a bias current path, the
inputs will float to a potential which exceeds the common-
mode range and the input amplifiers will saturate.
If the differential source resistance is low, the bias current
return path can be connected to one input (see the thermo-
couple example in Figure 3). With higher source impedance,
using two equal resistors provides a balanced input with
advantages of lower input offset voltage due to bias current
and better high-frequency common-mode rejection.
FIGURE 3. Providing an Input Common-Mode Current Path.
INPUT COMMON-MODE RANGE
The input common-mode range of the INA126/2126 is
shown in typical performance curves. The common-mode
range is limited on the negative side by the output voltage
swing of A2, an internal circuit node that cannot be measured
on an external pin. The output voltage of A2 can be ex-
pressed as:
VO2 = 1.25 VIN – (VIN – VIN) (10kΩ/RG) (2)
(Voltages referred to Ref terminal, pin 5)
–+–
The internal op amp A2 is identical to A1 and its output
swing is limited to typically 0.7V from the supply rails.
When the input common-mode range is exceeded (A2’s
output is saturated), A1 can still be in linear operation and
respond to changes in the non-inverting input voltage. The
output voltage, however, will be invalid.
LOW VOLTAGE OPERATION
The INA126/2126 can be operated on power supplies as low
as ±1.35V. Performance remains excellent with power sup-
plies ranging from ±1.35V to ±18V. Most parameters vary
only slightly throughout this supply voltage range—see
typical performance curves. Operation at very low supply
voltage requires careful attention to ensure that the common-
mode voltage remains within its linear range. See “Input
Common-Mode Voltage Range.”
The INA126/2126 can be operated from a single power
supply with careful attention to input common-mode range,
output voltage swing of both op amps and the voltage
applied to the Ref terminal. Figure 4 shows a bridge ampli-
fier circuit operated from a single +5V power supply. The
bridge provides an input common-mode voltage near 2.5V,
with a relatively small differential voltage.
INPUT PROTECTION
The inputs are protected with internal diodes connected to
the power supply rails. These diodes will clamp the applied
signal to prevent it from exceeding the power supplies by
more than approximately 0.7V. If the signal source voltage
can exceed the power supplies, the source current should be
limited to less than 10mA. This can generally be done with
a series resistor. Some signal sources are inherently current-
limited and do not require limiting resistors.
CHANNEL CROSSTALK—DUAL VERSION
The two channels of the INA2126 are completely indepen-
dent, including all bias circuitry. At DC and low frequency
there is virtually no signal coupling between channels.
Crosstalk increases with frequency and is dependent on
circuit gain, source impedance and signal characteristics.
As source impedance increases, careful circuit layout will
help achieve lowest channel crosstalk. Most crosstalk is
produced by capacitive coupling of signals from one channel
to the input section of the other channel. To minimize
coupling, separate the input traces as far as practical from
any signals associated with the opposite channel. A grounded
guard trace surrounding the inputs helps reduce stray cou-
pling between channels. Carefully balance the stray capaci-
tance of each input to ground, and run the differential inputs
of each channel parallel to each other, or directly adjacent on
top and bottom side of a circuit board. Stray coupling then
tends to produce a common-mode signal that is rejected by
the IA’s input.
47kΩ47kΩ
10kΩ
Microphone,
Hydrophone
etc.
Thermocouple
Center-tap provides
bias current return.
INA126
INA126
INA126
9
®
INA126, INA2126
FIGURE 4. Bridge Signal Acquisition—Single 5V Supply.
FIGURE 5. Differential Voltage-to-Current Converter.
A1IB Error
OPA177 ±1.5nA
OPA130 ±20pA
OPA602 ±1pA
OPA129 ±100fA
INA126
R
G
I
B
R
1
V
IN
–
+
A
1
I
O
Load
I
O
= • G
V
IN
R
1
Ref
✻
✻ Dual version has external sense connection.
40kΩ
10kΩ
10kΩ
40kΩ
INA126
51.2V
4
4
68
2
1
8
3
7
6
R
G
R
1
1kΩ
C
1
0.47µF
R
2
1kΩ
+5V
R
1
, C
1
, R
2
:
340Hz LP
Bridge
Sensor
2.5V – ∆V
2.5V + ∆V
REF1004C-1.2
33µA
2
3
1
+IN
–IN
V
REF
D
ADS7817
12-Bit
A/D C
S
Ck
6Serial
Data
Chip
Select
INA126 and ADS7817
are available in fine-pitch
MSOP-8 package
✻ Dual version has external
sense connection. Pin numbers
shown are for single version.
Clock
5
7
4
8
A
2
A
1
The ADS7817’s V
REF
input current is proportional to conversion rate. A
conversion rate 10kS/s or slower assures enough current to turn on the
reference diode. Converter input range is ±1.2V. Output swing limitation of
INA126 limits the A/D converter to somewhat greater than 11 bits of range.
A similar instrumentation amplifier, INA125, provides
an internal reference voltage for sensor excitation
and/or A/D converter reference.
✻
