©1995 Burr-Brown Corporation PDS-1296C Printed in U.S.A. October, 1996
A
1
A
2
A
3
40kΩ40kΩ
40kΩ40kΩ
V
IN
2
1
8
3
6
5
V
IN
R
G
V+
V–
INA128, INA129
Ref
V
O
INA128:
G = 1 + 50kΩ
R
G
INA129:
G = 1 + 49.4kΩ
R
G
–
+
Over-Voltage
Protection
25kΩ
(1)
25kΩ
(1)
Over-Voltage
Protection
4
7
NOTE: (1) INA129: 24.7kΩ
FEATURES
●LOW OFFSET VOLTAGE: 50µV max
●LOW DRIFT: 0.5µV/°C max
●LOW INPUT BIAS CURRENT: 5nA max
●HIGH CMR: 120dB min
●INPUTS PROTECTED TO ±40V
●WIDE SUPPLY RANGE: ±2.25 to ±18V
●LOW QUIESCENT CURRENT: 700µA
●8-PIN PLASTIC DIP, SO-8
DESCRIPTION
The INA128 and INA129 are low power, general
purpose instrumentation amplifiers offering excellent
accuracy. Their versatile 3-op amp design and small
size make them ideal for a wide range of applications.
Current-feedback input circuitry provides wide band-
width even at high gain (200kHz at G = 100).
A single external resistor sets any gain from 1 to
10,000. INA128 provides an industry standard gain
equation; INA129’s gain equation is compatible with
the AD620.
The INA128/INA129 is laser trimmed for very low
offset voltage (50µV), drift (0.5µV/°C) and high com-
mon-mode rejection (120dB at G ≥ 100). It operates
with power supplies as low as ±2.25V, and quiescent
current is only 700µA—ideal for battery operated
systems. Internal input protection can withstand up to
±40V without damage.
The INA128/INA129 is available in 8-pin plastic
DIP, and SO-8 surface-mount packages, specified for
the –40°C to +85°C temperature range. The INA128
is also available in dual configuration, the INA2128.
Precision, Low Power
INSTRUMENTATION AMPLIFIERS
®
INA128
INA129
APPLICATIONS
●BRIDGE AMPLIFIER
●THERMOCOUPLE AMPLIFIER
●RTD SENSOR AMPLIFIER
●MEDICAL INSTRUMENTATION
●DATA ACQUISITION
INA128
INA128
INA129
INA129
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
SPECIFICATIONS
At TA = +25°C, VS = ±15V, RL = 10kΩ, unless otherwise noted.
INA128P, U INA128PA, UA
INA129P, U INA129PA, UA
PARAMETER CONDITIONS MIN TYP MAX MIN TYP MAX UNITS
✻ Specification same as INA128P, U or INA129P, U.
NOTE: (1) Input common-mode range varies with output voltage—see typical curves. (2) Guaranteed by wafer test. (3) Temperature coefficient of the 50kΩ (or 49.4kΩ)
term in the gain equation. (4) Nonlinearity measurements in G = 1000 are dominated by noise. Typical nonlinearity is ±0.001%.
INPUT
Offset Voltage, RTI
Initial TA = +25°C±10 ±100/G ±50 ±500/G ±25 ±100/G ±125 ±1000/G µV
vs Temperature TA = TMIN to TMAX ±0.2 ± 2/G ±0.5 ± 20/G ±0.2 ± 5/G ±1 ± 20/G µV/°C
vs Power Supply VS = ±2.25V to ±18V ±0.2 ±20/G ±1 ±100/G ✻±2 ±200/G µV/V
Long-Term Stability ±0.1 ±3/G ✻µV/mo
Impedance, Differential 1010 || 2 ✻Ω || pF
Common-Mode 1011 || 9 ✻Ω || pF
Common-Mode Voltage Range(1) VO = 0V (V+) – 2 (V+) – 1.4 ✻✻ V
(V–) + 2 (V–) + 1.7 ✻✻ V
Safe Input Voltage ±40 ✻V
Common-Mode Rejection VCM = ±13V, ∆RS = 1kΩ
G=1 80 86 73 ✻dB
G=10 100 106 93 ✻dB
G=100 120 125 110 ✻dB
G=1000 120 130 110 ✻dB
BIAS CURRENT ±2±5✻±10 nA
vs Temperature ±30 ✻pA/°C
Offset Current ±1±5✻±10 nA
vs Temperature ±30 ✻pA/°C
NOISE VOLTAGE, RTI G = 1000, RS = 0Ω
f = 10Hz 10 ✻nV/√Hz
f = 100Hz 8 ✻nV/√Hz
f = 1kHz 8 ✻nV/√Hz
fB = 0.1Hz to 10Hz 0.2 ✻µVp-p
Noise Current
f=10Hz 0.9 ✻pA/√Hz
f=1kHz 0.3 ✻pA/√Hz
fB = 0.1Hz to 10Hz 30 ✻pAp-p
GAIN
Gain Equation, INA128 1 + (50kΩ/RG)✻V/V
INA129
1 + (49.4kΩ/R
G
)
✻
V/V
Range of Gain 1 10000 ✻✻V/V
Gain Error G=1 ±0.01 ±0.024 ✻±0.1 %
G=10 ±0.02 ±0.4 ✻±0.5 %
G=100 ±0.05 ±0.5 ✻±0.7 %
G=1000 ±0.5 ±1✻±2%
Gain vs Temperature(2) G=1 ±1±10 ✻✻ppm/°C
50kΩ (or 49.4kΩ) Resistance
(2, 3)
±25 ±100 ✻✻ppm/°C
Nonlinearity VO = ±13.6V, G=1 ±0.0001 ±0.001 ✻±0.002 % of FSR
G=10 ±0.0003 ±0.002 ✻±0.004 % of FSR
G=100 ±0.0005 ±0.002 ✻±0.004 % of FSR
G=1000 ±0.001 (Note 4) ✻✻% of FSR
OUTPUT
Voltage: Positive RL = 10kΩ(V+) – 1.4 (V+) – 0.9 ✻✻ V
Negative RL = 10kΩ(V–) + 1.4 (V–) + 0.8 ✻✻ V
Load Capacitance Stability 1000 ✻pF
Short-Circuit Current +6/–15 ✻mA
FREQUENCY RESPONSE
Bandwidth, –3dB G=1 1.3 ✻MHz
G=10 700 ✻kHz
G=100 200 ✻kHz
G=1000 20 ✻kHz
Slew Rate VO = ±10V, G=10 4 ✻V/µs
Settling Time, 0.01% G=1 7 ✻µs
G=10 7 ✻µs
G=100 9 ✻µs
G=1000 80 ✻µs
Overload Recovery 50% Overdrive 4 ✻µs
POWER SUPPLY
Voltage Range ±2.25 ±15 ±18 ✻✻ ✻V
Current, Total VIN = 0V ±700 ±750 ✻✻µA
TEMPERATURE RANGE
Specification –40 85 ✻✻°C
Operating –40 125 ✻✻°C
θ
JA 8-Pin Dip 80 ✻°C/W
SO-8 SOIC 150 ✻°C/W
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.
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.
ORDERING INFORMATION
PACKAGE
DRAWING TEMPERATURE
PRODUCT PACKAGE NUMBER(1) RANGE
INA128PA 8-Pin Plastic DIP 006 –40°C to +85°C
INA128P 8-Pin Plastic DIP 006 –40°C to +85°C
INA128UA SO-8 Surface-Mount 182 –40°C to +85°C
INA128U SO-8 Surface-Mount 182 –40°C to +85°C
INA129PA 8-Pin Plastic DIP 006 –40°C to +85°C
INA129P 8-Pin Plastic DIP 006 –40°C to +85°C
INA129UA SO-8 Surface-Mount 182 –40°C to +85°C
INA129U SO-8 Surface-Mount 182 –40°C to +85°C
NOTE: (1) For detailed drawing and dimension table, please see end of data
sheet, or Appendix C of Burr-Brown IC Data Book.
PIN CONFIGURATION
8-Pin DIP and SO-8
R
G
V
–IN
V
+IN
V–
R
G
V+
V
O
Ref
1
2
3
4
8
7
6
5
Top View
Supply Voltage .................................................................................. ±18V
Analog Input Voltage Range ............................................................. ±40V
Output Short-Circuit (to ground).............................................. Continuous
Operating Temperature ................................................. –40°C to +125°C
Storage Temperature ..................................................... –40°C to +125°C
Junction Temperature.................................................................... +150°C
Lead Temperature (soldering, 10s)............................................... +300°C
ABSOLUTE MAXIMUM RATINGS
TYPICAL PERFORMANCE CURVES
At T
A
= +25°C, V
S
= ±15V, unless otherwise noted.
COMMON-MODE REJECTION vs FREQUENCY
Frequency (Hz)
Common-Mode Rejection (dB)
10 100 10k 1M1k
140
120
100
80
60
40
20
0100k
G = 1V/V
G = 10V/V
G = 100V/V
G = 1000V/V
POSITIVE POWER SUPPLY REJECTION
vs FREQUENCY
Frequency (Hz)
Power Supply Rejection (dB)
140
120
100
80
60
40
20
010 100 1k 10k 100k 1M
G = 100V/V
G = 1000V/V
G = 1V/V
G = 10V/V
INPUT COMMON-MODE RANGE
vs OUTPUT VOLTAGE, VS = ±5, ±2.5V
Output Voltage (V)
Common-Mode Voltage (V)
–5
5
4
3
2
1
0
–1
–2
–3
–4
–5 –4 –3 –2 –1 0 1 2 3 4 5
VS = ±5V
VS = ±2.5V
G = 1 G = 1
G ≥ 10 G ≥ 10
G ≥ 10
G = 1
NEGATIVE POWER SUPPLY REJECTION
vs FREQUENCY
Frequency (Hz)
Power Supply Rejection (dB)
140
120
100
80
60
40
20
010 100 1k 10k 100k 1M
G = 100V/V
G = 1000V/V
G = 1V/V
G = 10V/V
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
G = 1 G = 1
G ≥ 10 G ≥ 10
V
D/2
–
+
–
+
V
CM
V
O
V
D/2
Ref
–15V
+15V
+
GAIN vs FREQUENCY
60
50
40
30
20
10
0
–10
–20
Gain (dB)
Frequency (Hz)
1k 10k 100k 1M 10M
G = 100V/V
G = 10V/V
G = 1V/V
G = 1000V/V
INPUT OVER-VOLTAGE V/I CHARACTERISTICS
5
4
3
2
1
0
–1
–2
–3
–4
–5
Input Current (mA)
Input Voltage (V)
–50 –40 –30 –20 –10 10 20 30 40050
G = 1V/V
G = 1V/V
G = 1000V/V
G = 1000V/V V
IN
I
IN
–15V
+15V
Flat region represents
normal linear operation.
TYPICAL PERFORMANCE CURVES (CONT)
At T
A
= +25°C, V
S
= ±15V, unless otherwise noted.
INPUT- REFERRED NOISE vs FREQUENCY
Frequency (Hz)
Input-Referred Voltage Noise (nV/√ Hz)
110 1k100
1k
100
10
110k
G = 1V/V
G = 10V/V
100
10
1
0.1
Input Bias Current Noise (pA/√ Hz)
Current Noise
G = 100, 1000V/V
SETTLING TIME vs GAIN
Gain (V/V)
Settling Time (µs)
100
10
11 10 100 1000
0.01%
0.1%
INPUT OFFSET VOLTAGE WARM-UP
10
8
6
4
2
0
–2
–4
–6
–8
–10 0100 200 300 400 500
Time (µs)
Offset Voltage Change (µV)
INPUT BIAS CURRENT vs TEMPERATURE
2
1
0
–1
–2–75 –50 –25 0 25 50 75 100 125
Temperature (°C)
Input Bias Current (nA)
I
OS
I
B
Typical I
B
and I
OS
Range ±2nA at 25°C
QUIESCENT CURRENT and SLEW RATE
vs TEMPERATURE
Temperature (°C)
Quiescent Current (µA)
0.85
0.8
0.75
0.7
0.65
0.6
6
5
4
3
2
1
–75 –50 –25 0 25 50 75 100 125
Slew Rate (V/µs)
IQ
Slew Rate
TYPICAL PERFORMANCE CURVES (CONT)
At T
A
= +25°C, V
S
= ±15V, unless otherwise noted.
OUTPUT VOLTAGE SWING
vs OUTPUT CURRENT
(V+)
(V+)–0.4
(V+)–0.8
(V+)–1.2
(V+)+1.2
(V–)+0.8
(V–)+0.4
V– 01234
Output Current (mA)
Output Voltage (V)
OUTPUT VOLTAGE SWING
vs POWER SUPPLY VOLTAGE
V+
(V+)–0.4
(V+)–0.8
(V+)–1.2
(V–)+1.2
(V–)+0.8
(V–)+0.4
V– 0 5 10 15 20
Power Supply Voltage (V)
Output Voltage Swing (V)
+25°C +85°C
–40°C
+25°C
–40°C
+85°C
R
L
= 10kΩ
+85°C
–40°C
SHORT-CIRCUIT OUTPUT CURRENT
vs TEMPERATURE
18
16
14
12
10
8
6
4
2
0–75 –50 –25 0 25 50 75 100 125
Temperature (°C)
Short Circuit Current (mA)
–I
SC
+I
SC
MAXIMUM OUTPUT VOLTAGE vs FREQUENCY
Frequency (Hz)
Peak-to-Peak Output Voltage (Vpp)
30
25
20
15
10
5
01k 10k 100k 1M
G = 1
G = 10, 100
G = 1000
TOTAL HARMONIC DISTORTION + NOISE
vs FREQUENCY
Frequency (Hz)
THD + N (%)
100 1k 10k
1
0.1
0.01
0.001 100k
V
O
= 1Vrms G = 1
R
L
= 10kΩ
G = 10V/V
R
L
= 100kΩ
G = 100, R
L
= 100kΩ
G = 1, R
L
= 100kΩ
500kHz Measurement
Bandwidth
Dashed Portion
is noise limited.
TYPICAL PERFORMANCE CURVES (CONT)
At T
A
= +25°C, V
S
= ±15V, unless otherwise noted.
LARGE-SIGNAL
(G = 1, 10)
SMALL-SIGNAL
(G = 100, 1000)
SMALL-SIGNAL
(G = 1, 10)
LARGE-SIGNAL
(G = 100, 1000)
VOLTAGE NOISE 0.1 to 10Hz
INPUT-REFERRED, G ≥ 100
20µs/div
5µs/div
20µs/div
5µs/div
1s/div
0.1µV/div
5V/div
G = 1
G = 10
5V/div
G = 100
G = 1000
20mV/div
G = 1
G = 10
20mV/div
G = 100
G = 1000
A
1
A
2
A
3
6
40kΩ40kΩ
40kΩ40kΩ
7
4
3
8
1
2
V
IN
V
IN
R
G
V+
V–
INA128, INA129
–
+5
Over-Voltage
Protection
25kΩ
(1)
25kΩ
(1)
Over-Voltage
Protection
Load
V
O
= G • (V
IN
– V
IN
)
+–
0.1µF
0.1µF
+
–
V
O
R
G
Also drawn in simplified form:
INA128
Ref
V
O
V
IN
–
V
IN
+
Ref
NOTE: (1) INA129: 24.7kΩ
APPLICATION INFORMATION
Figure 1 shows the basic connections required for operation
of the INA128/INA129. Applications with noisy or high
impedance power supplies may require decoupling capaci-
tors 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 assure 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 (G = 1).
SETTING THE GAIN
Gain is set by connecting a single external resistor, RG,
connected between pins 1 and 8:
INA129: (2)
Commonly used gains and resistor values are shown in
Figure 1.
The 50kΩ term in Equation 1 (49.4kΩ in Equation 2) comes
from the sum of the two internal feedback resistors of A1 and
A2. These on-chip metal film resistors are laser trimmed to
INA128: (1)
G=1+50kΩ
R
G
FIGURE 1. Basic Connections.
accurate absolute values. The accuracy and temperature
coefficient of these internal resistors are included in the gain
accuracy and drift specifications of the INA128/INA129.
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 (possi-
bly an unstable gain error) in gains of approximately 100 or
greater.
DYNAMIC PERFORMANCE
The typical performance curve “Gain vs Frequency” shows
that, despite its low quiescent current, the INA128/INA129
achieves wide bandwidth, even at high gain. This is due to
the current-feedback topology of the input stage circuitry.
Settling time also remains excellent at high gain.
NOISE PERFORMANCE
The INA128/INA129 provides very low noise in most appli-
cations. Low frequency noise is approximately 0.2µVp-p
measured from 0.1 to 10Hz (G ≥ 100). This provides
dramatically improved noise when compared to state-of-the-
art chopper-stabilized amplifiers.
G=1+49.4kΩ
R
G
DESIRED RGNEAREST RGNEAREST
GAIN (V/V) (Ω) 1% RG (Ω)(Ω) 1% RG (Ω)
1NCNCNCNC
2 50.00k 49.9k 49.4k 49.9k
5 12.50k 12.4k 12.35k 12.4k
10 5.556k 5.62k 5489 5.49k
20 2.632k 2.61k 2600 2.61k
50 1.02k 1.02k 1008 1k
100 505.1 511 499 499
200 251.3 249 248 249
500 100.2 100 99 100
1000 50.05 49.9 49.5 49.9
2000 25.01 24.9 24.7 24.9
5000 10.00 10 9.88 9.76
10000 5.001 4.99 4.94 4.87
NC: No Connection.
INA128 INA129
50kΩ
RG
INA128:
G = 1 +
INA129:
G = 1 + 49.4kΩ
RG
OFFSET TRIMMING
The INA128/INA129 is laser trimmed for low offset voltage
and offset voltage drift. Most applications require no exter-
nal offset adjustment. Figure 2 shows an optional circuit for
trimming the output offset voltage. The voltage applied to
Ref terminal is summed with the output. The op amp buffer
provides low impedance at the Ref terminal to preserve good
common-mode rejection.
INPUT BIAS CURRENT RETURN PATH
The input impedance of the INA128/INA129 is extremely
high—approximately 1010Ω. However, a path must be pro-
vided for the input bias current of both inputs. This input
bias current is approximately ±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 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
possible advantages of lower input offset voltage due to bias
current and better high-frequency common-mode rejection.
INPUT COMMON-MODE RANGE
The linear input voltage range of the input circuitry of the
INA128/INA129 is from approximately 1.4V below the
positive supply voltage to 1.7V above the negative supply.
As a differential input voltage causes the output voltage
increase, however, the linear input range will be limited by
the output voltage swing of amplifiers A1 and A2. So the
FIGURE 2. Optional Trimming of Output Offset Voltage.
10kΩ
OPA177
±10mV
Adjustment Range
100Ω
100Ω
100µA
1/2 REF200
100µA
1/2 REF200
V+
V–
R
G
INA128
Ref
V
O
V
IN
–
V
IN
+
FIGURE 3. Providing an Input Common-Mode Current Path.
47kΩ47kΩ
10kΩ
Microphone,
Hydrophone
etc.
Thermocouple
Center-tap provides
bias current return.
INA128
INA128
INA128
linear common-mode input range is related to the output
voltage of the complete amplifier. This behavior also de-
pends on supply voltage—see performance curves “Input
Common-Mode Range vs Output Voltage”.
Input-overload can produce an output voltage that appears
normal. For example, if an input overload condition drives
both input amplifiers to their positive output swing limit, the
difference voltage measured by the output amplifier will be
near zero. The output of A3 will be near 0V even though both
inputs are overloaded.
LOW VOLTAGE OPERATION
The INA128/INA129 can be operated on power supplies as
low as ±2.25V. Performance remains excellent with power
supplies ranging from ±2.25V 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 assure that the input
voltages remain within their linear range. Voltage swing
requirements of internal nodes limit the input common-
mode range with low power supply voltage. Typical perfor-
mance curves, “Input Common-Mode Range vs Output
Voltage” show the range of linear operation for ±15V, ±5V,
and ±2.5V supplies.
INA128
R
G
V
O
C
1
0.1µF
OPA130
Ref R
1
1MΩ
f
–3dB
= 1
2πR
1
C
1
= 1.59Hz
V
IN
+
–
FIGURE 4. ECG Amplifier With Right-Leg Drive.
FIGURE 8. Differential Voltage to Current Converter.
A1IB Error
OPA177 ±1.5nA
OPA131 ±50pA
OPA602 ±1pA
OPA128 ±75fA
SEEBECK
ISA COEFFICIENT
TYPE MATERIAL (µV/°C) R1, R 2
E + Chromel 58.5 66.5kΩ
– Constantan
J + Iron 50.2 76.8kΩ
– Constantan
K + Chromel 39.4 97.6kΩ
– Alumel
T + Copper 38.0 102kΩ
– Constantan
FIGURE 7. Thermocouple Amplifier With RTD Cold-
Junction Compensation.
FIGURE 5. Bridge Amplifier.
FIGURE 6. AC-Coupled Instrumentation Amplifier.
REF102
R
2
R
1
R
3
Pt100
Cu
Cu
V+
K
6
10.0V
4
2
INA128 V
O
Ref
100Ω = Pt100 at 0°C
R
G
INA128
R
G
I
B
R
1
V
IN
–
+
A
1
I
O
Load
I
O
= • G
V
IN
R
1
Ref
INA128
R
G
/2
R
G
= 5.6kΩ
V
O
LA
RL
RA
10kΩ
Ref
NOTE: Due to the INA128’s current-feedback
topology, V
G
is approximately 0.7V less than
the common-mode input voltage. This DC offset
in this guard potential is satisfactory for many
guarding applications.
G = 10
2.8kΩ
V
G
V
G
2.8kΩ
1/2
OPA2131
390kΩ
390kΩ
1/2
OPA2131
300Ω
+5V
2.5V – ∆V
2.5V + ∆V
R
G
INA128 V
O
Ref
