INA331
INA2331
SBOS215C – DECEMBER 2001 – REVISED APRIL 2005
DESCRIPTION
The INA331 and INA2331 are rail-to-rail output, low-power
CMOS instrumentation amplifiers that offer wide range, single-
supply operation as well as bipolar-supply operation. The
INA331 family provides low-cost, low-noise amplification of
differential signals with a low quiescent current of 415µA
(dropping to 0.01µA when shutdown). Returning to normal
operation within microseconds, this INA can be used for
battery or multi-channel applications.
Configured internally in a gain of 5V/V, the INA331 offers
flexibility in higher gains by choosing external resistors.
FEATURES
● DESIGNED FOR LOW COST
● HIGH GAIN ACCURACY: G = 5, 0.02%, 2ppm/°C
● GAIN SET WITH EXT. RESISTORS FOR > 5V/V
● LOW OFFSET VOLTAGE: ±250µV
● HIGH CMRR: 94dB DC, 50dB at 45kHz
● LOW BIAS CURRENT: 0.5pA
● BANDWIDTH, SLEW RATE: 2.0MHz, 5V/µs
● RAIL-TO-RAIL OUTPUT SWING: (V+) – 0.02V
● WIDE TEMPERATURE RANGE: –55°C to +125°C
● LOW QUIESCENT CURRENT: 490µA max/chan
● SHUT DOWN: 0.01µA
● MSOP-8 SINGLE AND TSSOP-14 DUAL PACKAGES
Copyright © 2001-2005, Texas Instruments Incorporated
Low-Power, Single-Supply, CMOS
INSTRUMENTATION AMPLIFIERS
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
● INDUSTRIAL SENSOR AMPLIFIERS:
Bridge, RTD, Thermocouple, Position
● PHYSIOLOGICAL AMPLIFIERS:
ECG, EEG, EMG
● A/D CONVERTER SIGNAL CONDITIONING
● DIFFERENTIAL LINE RECEIVERS WITH GAIN
● FIELD UTILITY METERS
● PCMCIA CARDS
● AUDIO AMPLIFIERS
● COMMUNICATION SYSTEMS
● TEST EQUIPMENT
● AUTOMOTIVE INSTRUMENTATION
The INA331 rejects line noise and its harmonics, because
common-mode error remains low even at higher frequencies.
High bandwidth and slew rate makes the INA331 ideal for
directly driving sampling Analog-to-Digital (A/D) converters
as well as general-purpose applications.
With high precision, low cost, and small packages, the
INA331 outperforms discrete designs. They are specified for
a wide temperature range of –55°C to +125°C.
A2
A1 A3
40kΩ
VREF
VIN–
VIN+
10kΩ
10kΩ
ShutdownV+
VOUT
G = 5 + (5R2/R1)
V–
R2
R1
RG
40kΩCh A
INA2331
INA331
Ch B
®
INA2331
INA331
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.
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All trademarks are the property of their respective owners.
INA331, INA2331
SBOS215C
2www.ti.com
Supply Voltage, V+ to V–.................................................................... 7.5V
Signal Input Terminals, Voltage(2) .....................(V–) – 0.5V to (V+) + 0.5V
Current(2) ..................................................... 10mA
Output Short-Circuit(3) .............................................................. Continuous
Operating Temperature .................................................. –55°C to +125°C
Storage Temperature...................................................... –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. (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. (3) Short-circuit to ground, one amplifier per
package.
ABSOLUTE MAXIMUM RATINGS(1) ELECTROSTATIC
DISCHARGE SENSITIVITY
This integrated circuit can be damaged by ESD. Texas Instru-
ments recommends that all integrated circuits be handled with
appropriate 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.
PIN CONFIGURATION
Top View
RG
V
IN
–
V
IN
+
V–
Shutdown
V+
V
OUT
REF
INA331
MSOP-8 (DGK)
1
2
3
4
8
7
6
5
1
2
3
4
5
6
7
14
13
12
11
10
9
8
Shutdown A
VOUTA
REFA
V+
REFB
VOUTB
Shutdown B
RGA
VIN–A
VIN+A
V–
VIN+B
VIN–B
RGB
INA2331
Dual, TSSOP-14 (PW)
PACKAGE PACKAGE
PRODUCT PACKAGE-LEAD DESIGNATOR MARKING
Single
INA331IDGK MSOP-8 DGK C31
INA331AIDGK MSOP-8 DGK C31
Dual
INA2331AIPW TSSOP-14 PW 2331A
NOTES: (1) For the most current package and ordering information, see the Package Option Addendum at the end of this document, or see the TI website at
www.ti.com.
PACKAGE/ORDERING INFORMATION(1)
INA331, INA2331
SBOS215C 3
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ELECTRICAL CHARACTERISTICS: VS = +2.7V to +5.5V
Boldface limits apply over the specified temperature range, TA = –55°C to 125°C.
At TA = +25°C, RL = 10kΩ, G = 25, and VREF = VS/ 2, unless otherwise noted.
INA331AIDGK
INA331IDGK INA2331AIPW
PARAMETER CONDITION MIN TYP MAX MIN TYP MAX UNITS
INPUT
Input Offset Voltage, RTI VS = +5V ±250 ±500 ✻±1000 µV
Over Temperature VOS ±1.7 ±2.1 mV
Temperature Coefficient dVOS/dT ±5✱µV/°C
vs Power Supply PSRR VS = +2.7V to +5.5V ±50 ±200 ✻✻µV/V
vs Temperature ±220 ✱µV/V
Long-Term Stability ±0.4 ✻µV/month
Input Impedance 1013 || 3 ✻Ω || pF
Input Common-Mode Range VS = 2.7V 0.35 1.5 ✻✻V
VS = 5V 0.55 3.8 ✻✻V
Common-Mode Rejection CMRR VS = 5V, VCM = 0.55V to 3.8V 90 94 80 ✻dB
–40°C to +85°CV
S = 5V, VCM = 0.55V to 3.8V 77 75 dB
Over Temperature VS = 5V, VCM = 0.55V to 3.8V 72 70 dB
VS = 2.7V, VCM = 0.35V to 1.5V 94 ✻dB
Crosstalk, Dual 114 dB
INPUT BIAS CURRENT VCM = VS/2
Bias Current IB±0.5 ±10 ✻✻pA
Offset Current IOS ±0.5 ±10 ✻✻pA
NOISE, RTI RS = 0Ω
Voltage Noise: f = 10Hz eN280 ✻nV/√Hz
f = 100Hz 96 ✻nV/√Hz
f = 1kHz 46 ✻nV/√Hz
f = 0.1Hz to 10Hz 7 ✻µVPP
Current Noise: f = 1kHz iN0.5 ✻fA/√Hz
GAIN(1)
Gain Equation, Externally Set G > 5 G = 5 + (5R2/R1)✻
Range of Gain 5 1000 ✻✻V/V
Gain Error G = 5 ±0.02 ±0.1 ✻✻%
vs Temperature G = 5 ±2±10 ✱✱ppm/°C
Nonlinearity
G = 25
(2)
, V
S
= 5V, V
O
= 0.05 to 4.95
±0.001 ±0.010 ✻✻% of FS
Over Temperature ±0.002 ±0.015 ✱✱% of FS
OUTPUT
Output Voltage Swing from Rail(3) RL = 10kΩ50 25 ✻✻ mV
Over Temperature G > 10 50 ✱mV
Capacitance Load Drive See Typical Characteristics ✻pF
Short-Circuit Current +48/–32 ✻mA
FREQUENCY RESPONSE
Bandwidth, –3dB BW G = 25 2.0 ✻MHz
Slew Rate SR VS = 5V, G = 25 5 ✻V/µs
Settling Time, 0.1% tSG = 25, CL = 100pF, VO = 2V step 1.7 ✻µs
0.01% 2.5 ✻µs
Overload Recovery 50% Input Overload G = 25 2 ✻µs
POWER SUPPLY
Specified Voltage Range +2.7 +5.5 ✻✻V
Operating Voltage Range +2.5 to +5.5 ✻V
Quiescent Current per Channel IQVSD > 2.5(3) 415 490 ✻✻µA
Over Temperature 600 ✱µA
Shutdown Quiescent Current/Chan ISD VSD < 0.8(3) 0.01 1 ✻✻µA
TEMPERATURE RANGE
Specified/Operating Range –55 +125 ✻✻°C
Storage Range –65 +150 ✻✻°C
Thermal Resistance
θ
JA
MSOP-8, TSSOP-14 Surface Mount
150 ✻°C/W
✻ Specifications same as INA331IDGK
NOTES: (1) Does not include errors from external gain setting resistors.
(2) Output voltage swings are measured between the output and power-supply rails. Output swings to rail only if G ≥ 10. Output does not swing to positive
rail if gain is less than 10.
(3) See typical characteristic
Percent Overshoot vs Load Capacitance
.
(4) See typical characteristic
Shutdown Voltage vs Supply Voltage
.
INA331, INA2331
SBOS215C
4www.ti.com
TYPICAL CHARACTERISTICS
At TA = +25°C, VS = 5V, VCM = VS/2, RL = 10kΩ, and CL = 100pF, unless otherwise noted.
GAIN vs FREQUENCY
10
Gain (dB)
Frequency (Hz)
100 1k 10k 100k 1M 10M
80
70
60
50
40
30
20
10
0
–10
–20
Gain = 500
Gain = 100
Gain = 25
Gain = 5
COMMON-MODE REJECTION RATIO
vs FREQUENCY
10
CMRR (dB)
Frequency (Hz)
100 1k 10k 100k
120
100
80
60
40
20
0
POWER-SUPPLY REJECTION RATIO
vs FREQUENCY
1
PSRR (dB)
Frequency (Hz)
10 100 1k 10k 100k
100
90
80
70
60
50
40
30
20
10
0
MAXIMUM OUTPUT VOLTAGE vs FREQUENCY
100
Maximum Output Voltage (VPP)
Frequency (Hz)
1k 10k 100k 1M 10M
6
5
4
3
2
1
0
VS = 5.5V
VS = 5.0V
VS = 2.7V
NOISE vs FREQUENCY
1
V
NOISE
(nV/√Hz)
I
NOISE
(fA/√Hz)
Frequency (Hz)
10 100 1k 10k 100k
10k
1k
100
10
100
10
1
0.1
0.1Hz TO 10Hz VOLTAGE NOISE
1s/div
2µV/div
INA331, INA2331
SBOS215C 5
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TYPICAL CHARACTERISTICS (Cont.)
At TA = +25°C, VS = 5V, VCM = VS/2, RL = 10kΩ, and CL = 100pF, unless otherwise noted.
COMMON-MODE INPUT RANGE
vs REFERENCE VOLTAGE
0
Output—Referred to Ground (V)
Input Common-Mode Voltage (V)
12345
6
5
4
3
2
1
0
Outside of Normal Operation
REF
Increasing
QUIESCENT CURRENT AND SHUTDOWN CURRENT
vs POWER SUPPLY
I
Q
(µA), I
SD
(nA)
Supply Voltage (V)
2.5 3 3.5 4 4.5 5 5.5
500
450
400
350
300
250
200
150
100
50
0
I
Q
I
SD
SHORT-CIRCUIT CURRENT vs POWER SUPPLY
ISC (mA)
Supply Voltage (V)
2.5 3 3.5 4 4.5 5 5.5
60
50
40
30
20
10
0
ISC+
ISC–
SHORT-CIRCUIT CURRENT vs TEMPERATURE
I
SC
(mA)
Temperature (°C)
–75 25–50 –25 0 50 75 100 125 150
60
50
40
30
20
10
0
I
SC+
I
SC–
OUTPUT SWING vs LOAD RESISTANCE
Swing-to-Rail (mV)
RLOAD (Ω)
0 10k 20k 30k 40k 50k
25
20
15
10
5
0
To Positive Rail
To Negative Rail
QUIESCENT CURRENT AND SHUTDOWN CURRENT
vs TEMPERATURE
IQ (µA)
Temperature (°C)
–75 –50 –25 0 25 50 75 100 125 150
600
550
500
450
400
350
300
250
200
150
100
50
0
IQ
ISD
INA331, INA2331
SBOS215C
6www.ti.com
TYPICAL CHARACTERISTICS (Cont.)
At TA = +25°C, VS = 5V, VCM = VS/2, RL = 10kΩ, and CL = 100pF, unless otherwise noted.
SMALL-SIGNAL STEP RESPONSE (G = 5)
4µs/div
100mV/div
SMALL-SIGNAL STEP RESPONSE (G = 100)
4µs/div
50mV/div
SMALL-SIGNAL STEP RESPONSE
(G = 5, CL = 1000pF)
4µs/div
100mV/div
SMALL-SIGNAL STEP RESPONSE
(G = 100, CL = 1000pF)
10µs/div
50mV/div
SMALL-SIGNAL STEP RESPONSE
(G = 100, CL = 4700pF)
10µs/div
50mV/div
LARGE-SIGNAL STEP RESPONSE (G = 25)
10µs/div
1V/div
INA331, INA2331
SBOS215C 7
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TYPICAL CHARACTERISTICS (Cont.)
At TA = +25°C, VS = 5V, VCM = VS/2, RL = 10kΩ, and CL = 100pF, unless otherwise noted.
SETTLING TIME vs GAIN
1 10 100 1k
Gain (V/V)
Settling Time (µs)
60
50
40
30
20
10
0
Output 2V
PP
Differential
Input Drive
0.01%
0.1%
PERCENT OVERSHOOT vs LOAD CAPACITANCE
10 100 1k 10k
Load Capacitance (pF)
Overshoot (%)
100
90
80
70
60
50
40
30
20
10
0
Output 100mV
PP
Differential Drive
G = 5
G = 25
SHUTDOWN VOLTAGE vs SUPPLY VOLTAGE
2.5
Shutdown (V)
Supply Voltage (V)
3 3.5 4 4.5 5 5.5
3
2.5
2
1.5
1
0.5
0
Normal Operation Mode
Part Draws Below 1µA Quiescent Current
Operation in this Region
is not Recommended
Shutdown Mode
SHUTDOWN TRANSIENT BEHAVIOR
50µs/div
1V/div
VSD
VOUT
25
20
15
10
5
0
–1.0
–0.9
–0.8
–0.7
–0.6
–0.5
–0.4
–0.3
–0.2
–0.1
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
Offset Voltage (mV)
Percentage of Amplifiers (%)
OFFSET VOLTAGE PRODUCTION DISTRIBUTION
20
18
16
14
12
10
8
6
4
2
0
–14
–13
–11
–10
–8
–7
–6
–4
–3
–1
0
1
3
4
6
7
8
10
11
13
14
Offset Voltage (µV/°C)
Percentage of Amplifiers (%)
OFFSET VOLTAGE DRIFT
PRODUCTION DISTRIBUTION
INA331, INA2331
SBOS215C
8www.ti.com
TYPICAL CHARACTERISTICS (Cont.)
At TA = +25°C, VS = 5V, VCM = VS/2, RL = 10kΩ, and CL = 100pF, unless otherwise noted.
SLEW RATE vs TEMPERATURE
Slew Rate (V/µs)
Temperature (°C)
–75 25–50 –25 0 50 75 100 125 150
8
7
6
5
4
3
2
1
0
OUTPUT VOLTAGE SWING vs OUTPUT CURRENT
Output Voltage (V)
Output Current (mA)
0 5 10 15 25 35 45 5520 30 40 50 60
5
4
3
2
1
0
125°C25°C–55°C
INPUT BIAS CURRENT vs TEMPERATURE
Input Bias Current (pA)
Temperature (°C)
–75 25–50 –25 0 50 75 100 125 150
10000
1000
100
10
1
0.1
CHANNEL SEPARATION vs FREQUENCY
Separation (dB)
Frequency (Hz)
1 10k10 100 1k 100k 1M 10M
120
100
80
60
40
20
0
INA331, INA2331
SBOS215C 9
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APPLICATIONS INFORMATION
The INA331 is a modified version of the classic “two op amp”
instrumentation amplifier, with an additional gain amplifier.
Figure 1 shows the basic connections for the operation of the
INA331 and INA2331. The power supply should be capaci-
tively decoupled with 0.1µF capacitors as close to the INA331
as possible for noisy or high-impedance applications.
The output is referred to the reference terminal, which must
be at least 1.2V below the positive supply rail.
OPERATING VOLTAGE
The INA331 family is fully specified over a supply range of
+2.7V to +5.5V, with key parameters tested over the tempera-
ture range of –55°C to +125°C. Parameters that vary signifi-
cantly with operating conditions, such as load conditions or
temperature, are shown in the Typical Characteristics.
The INA331 may be operated on a single supply. Figure 2
shows a bridge amplifier circuit operated from a single +5V
supply. The bridge provides a small differential voltage riding
on an input common-mode voltage.
FIGURE 2. Single-Supply Bridge Amplifier.
FIGURE 1. Basic Connections.
40kΩ10kΩ
10kΩ
40kΩ
3
2
5
1
78 4Also drawn in simplified form:
6
REF
0.1µF0.1µF
RG
V
IN
–
V
IN
+
V–
V+
A1 A3
A2
V
O
= ((V
IN
+) – (V
IN
–)) • G
Short V
OUT
to RG
for G = 5 5
10
50
100
SHORT
100kΩ
90kΩ
190kΩ
OPEN
100kΩ
10kΩ
10kΩ
R
2
R
1
Shutdown (For Single
Supply)
DESIRED GAIN
(V/V) R
1
R
2
G = 5 + 5 (R
2
/ R
1
)
INA331
5
3
2
V
OUT
8
7
6
41
V+ Shutdown
RG
V
IN
–
V–
V
IN
+
REF
Bridge
Sensor
+5V
NOTE: (1) REF should be adjusted for the desired output level,
keeping in mind that the value of REF affects the common-mode
input range. See Typical Characteristics.
INA331
5
3
2
V
OUT
8
7
6
4
1
V+ Shutdown
RG
V
IN
–
V–
V
IN
+
REF
(1)
INA331, INA2331
SBOS215C
10 www.ti.com
SETTING THE GAIN
The ratio of R2 to R1, or the impedance between pins 1, 5,
and 6, determines the gain of the INA331. With an internally
set gain of 5, the INA331 can be programmed for gains
greater than 5 according to the following equation:
G = 5 + 5 (R2/R1)
The INA331 is designed to provide accurate gain, with gain
error less than 0.1%. Setting gain with matching TC resistors
will minimize gain drift. Errors from external resistors will add
directly to the error, and may become dominant error sources.
COMMON-MODE INPUT RANGE
The upper limit of the common-mode input range is set by the
common-mode input range of the second amplifier, A2, to
1.2V below positive supply. Under most conditions, the
amplifier operates beyond this point with reduced perfor-
mance. The lower limit of the input range is bounded by the
output swing of amplifier A1, and is a function of the refer-
ence voltage according to the following equation:
VOA1 = 5/4 VCM – 1/4 VREF
(See typical characteristics
Common-Mode Input Range vs
Reference Voltage
.)
REFERENCE
The reference terminal defines the zero output voltage level.
In setting the reference voltage, the common-mode input of
A3 should be considered according to the following equation:
VOA2 = VREF + 5 (VIN+ – VIN–)
For ensured operation, VOA2 should be less than
VDD – 1.2V.
The reference pin requires a low-impedance connection. As
little as 160Ω in series with the reference pin will degrade the
CMRR to 80dB. The reference pin may be used to compen-
sate for the offset voltage (see Offset Trimming section). The
reference voltage level also influences the common-mode
input range (see Common-Mode Input Range section).
INPUT BIAS CURRENT RETURN
With a high input impedance of 1013Ω, the INA331 is ideal for
use with high-impedance sources. The input bias current of
less than 10pA makes the INA331 nearly independent of
input impedance and ideal for low-power applications.
For proper operation, a path must be provided for input bias
currents for both inputs. Without input bias current paths, the
inputs will “float” to a potential that exceeds common-mode
range and the input amplifier will saturate. Figure 3 shows
FIGURE 3. Providing an Input Common-Mode Path.
how the bias current path can be provided in the cases of
microphone applications, thermistor applications, ground re-
turns, and dc-coupled resistive bridge applications.
When differential source impedance is low, the bias current
return path can be connected to one input. With higher
source impedance, two equal resistors will provide a bal-
anced input. The advantages are lower input offset voltage
due to bias current flowing through the source impedance
and better high-frequency gain.
47kΩ
Microphone,
Hydrophone,
etc.
Center-tap
provides bias
current return
Bridge resistance
provides bias
current return
Transformer
Bridge
Amplifier
Bridge
Sensor
VB(1)
VB(1)
VEX
NOTE: (1) VB is bias voltage within
common-mode range, dependent
on REF.
INA331
5
3
2
8
7
6
41
V+ Shutdown
VIN–
V–
VIN
+
REF
INA331
5
3
2
8
7
6
41
V+ Shutdown
VIN–
V–
VIN
+
REF
INA331
5
3
2
8
7
6
41
V+ Shutdown
VIN–
V–
VIN
+
REF
VOUT
RG
VOUT
RG
VOUT
RG
INA331, INA2331
SBOS215C 11
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SHUTDOWN MODE
The shutdown pin of the INA331 is nominally connected to V+.
When the pin is pulled below 0.8V on a 5V supply, the INA331
goes into sleep mode within nanoseconds. For actual shut-
down threshold, see the typical characteristic
Shutdown Volt-
age vs Supply Voltage
. Drawing less than 2µA of current, and
returning from sleep mode in microseconds, the shutdown
feature is useful for portable applications. Once in ‘sleep-
mode’ the amplifier has high output impedance, making the
INA331 suitable for multiplexing.
RAIL-TO-RAIL OUTPUT
A class AB output stage with common-source transistors is
used to achieve rail-to-rail output for gains of 10 or greater.
For resistive loads greater than 10kΩ, the output voltage
can swing to within 25mV of the supply rail while maintain-
ing low gain error. For heavier loads and over temperature,
see the typical characteristic
Output Voltage Swing vs
Output Current
. The INA331’s low output impedance at high
frequencies makes it suitable for directly driving Capacitive-
Input A/D converters, as shown in Figure 4.
FIGURE 4. INA331 Directly Drives Capacitive-Input, High-
Speed A/D Converter.
OUTPUT BUFFERING
The INA331 is optimized for a load impedance of 10kΩ or
greater. For higher output current the INA331 can be buff-
ered using the OPA340, as shown in Figure 5. The OPA340
can swing within 50mV of the supply rail, driving a 600Ω load.
The OPA340 is available in the tiny MSOP-8 package.
OFFSET TRIMMING
The INA331 is laser trimmed for low offset voltage. In the
event that external offset adjustment is required, the offset
can be adjusted by applying a correction voltage to the
reference terminal. Figure 6 shows an optional circuit for
trimming offset voltage. The voltage applied to the REF
terminal is added to the output signal. The gain from REF to
VOUT is +1. An op amp buffer is used to provide low
impedance at the REF terminal to preserve good common-
mode rejection. FIGURE 7. Sample Output Buffering Circuit.
INPUT PROTECTION
Device inputs are protected by ESD diodes that will conduct
if the input voltages exceed the power supplies by more than
500mV. Momentary voltages greater than 500mV beyond
the power supply can be tolerated if the current through the
input pins is limited to 10mA. This is easily accomplished with
input resistor RLIM, as shown in Figure 7. Many input signals
are inherently current-limited to less than 10mA; therefore, a
limiting resistor is not required.
ADS7818
or
ADS7822
12-Bits
+5V
INA331
5
3
2
VOUT
8
7
6
41
V+ Shutdown
RG
VIN–
V–
VIN+
REF
fS < 100kHz
OPA340 V
OUT
+5V
0.1µF
0.1µF
INA331
5
3
2
V
OUT
8
7
6
41
V+ Shutdown
RG
V
IN
–
V–
V
IN
+
REF
FIGURE 5. Output Buffering Circuit. Able to drive loads as
low as 600Ω.
FIGURE 6. Optional Offset Trimming Voltage.
OPA336 Adjustable
Voltage
INA331
5
3
2
V
OUT
8
7
6
41
V+ Shutdown
RG
V
IN
–
V–
V
IN
+
REF
(1)
NOTE: (1) REF should be adjusted for the desired output level.
The value of REF affects the common-mode input range.
R
LIM
R
LIM
I
OVERLOAD
10mA max INA331
5
3
2
V
OUT
8
7
6
41
V+ Shutdown
RG
V
IN
–
V–
V
IN
+
REF
INA331, INA2331
SBOS215C
12 www.ti.com
OFFSET VOLTAGE ERROR CALCULATION
The offset voltage (VOS) of the INA331IDGK is specified at a
maximum of 500µV with a +5V power supply and the com-
mon-mode voltage at VS/2. Additional specifications for power-
supply rejection and common-mode rejection are provided to
allow the user to easily calculate worst-case expected offset
under the conditions of a given application.
Power-Supply Rejection Ratio (PSRR) is specified in µV/V.
For the INA331, worst case PSRR is 200µV/V, which means
for each volt of change in power supply, the offset may shift
up to 200µV. Common-Mode Rejection Ratio (CMRR) is
specified in dB, which can be converted to µV/V using the
following equation:
CMRR (in µV/V) = 10[(CMRR in dB)/–20] • 106
For the INA331, the worst case CMRR over the specified
common-mode range is 90dB (at G = 25) or about 30µV/V
This means that for every volt of change in common-mode,
the offset will shift less than 30µV.
These numbers can be used to calculate excursions from the
specified offset voltage under different application condi-
tions. For example, an application might configure the ampli-
fier with a 3.3V supply with 1V common-mode. This configu-
ration varies from the specified configuration, representing a
1.7V variation in power supply (5V in the offset specification
versus 3.3V in the application) and a 0.65V variation in
common-mode voltage from the specified VS/2.
Calculation of the worst-case expected offset would be as
follows:
Adjusted VOS = Maximum specified VOS +
(power-supply variation) • PSRR +
(common-mode variation) • CMRR
VOS = 0.5mV + (1.7V • 200µV) + (0.65V • 30µV)
= ±0.860mV
However, the typical value will be smaller, as seen in the
Typical Characteristics.
FEEDBACK CAPACITOR IMPROVES RESPONSE
For optimum settling time and stability with high-impedance
feedback networks, it may be necessary to add a feedback
capacitor across the feedback resistor, RF, as shown in
Figure 8. This capacitor compensates for the zero created by
the feedback network impedance and the INA331’s RG-pin
input capacitance (and any parasitic layout capacitance).
The effect becomes more significant with higher impedance
networks. Also, RX and CL can be added to reduce high-
frequency noise.
It is suggested that a variable capacitor be used for the
feedback capacitor since input capacitance may vary be-
tween instrumentation amplifiers, and layout capacitance is
difficult to determine. For the circuit shown in Figure 8, the
value of the variable feedback capacitor should be chosen by
the following equation:
RIN • CIN = RF • CF
Where CIN is equal to the INA331’s RG-pin input capacitance
(typically 3pF) plus the layout capacitance. The capacitor can
be varied until optimum performance is obtained.
FIGURE 8. Feedback Capacitor Improves Dynamic Perfor-
mance.
INA331
V+
V
OUT
R
IN
R
IN
• C
IN
= R
F
•
C
F
R
F
R
X
C
L
C
IN
Where C
IN
is equal to the INA331’s input capacitance
(approximately 3pF) plus any parastic layout capacitance.
5
3
2
8
7
6
4
1
Shutdown
RG
V
IN
–
V–
V
IN+
REF
C
F
INA331, INA2331
SBOS215C 13
www.ti.com
APPLICATION CIRCUITS
MEDICAL ECG APPLICATIONS
Figure 9 shows the INA331 configured to serve as a low-cost
ECG amplifier, suitable for moderate accuracy heart-rate
applications such as fitness equipment. The input signals are
obtained from the left and right arms of the patient. The
common-mode voltage is set by two 2MΩ resistors. This
potential through a buffer provides an optional right leg drive.
Filtering can be modified to suit application needs by chang-
ing the capacitor value of the output filter.
LOW-POWER, SINGLE-SUPPLY DATA
ACQUISITION SYSTEMS
Refer to Figure 4 to see the INA331 configured to drive an
ADS7818. Functioning at frequencies of up to 500kHz, the
INA331 is ideal for low-power data acquisition.
FIGURE 9. Simplified ECG Circuit for Medical Applications.
OPA336
OPA336
1MΩ
REF
1MΩ
1MΩ
10kΩ
10kΩ
2kΩ
2kΩ
1.6nF
0.1µF
100kΩ
100kΩ
+5V
V
R
V
R
V
R
= +2.5V
2MΩ2MΩ
INA331
5
3
2
8
7
6
41
V+ Shutdown
RG
V
IN
–
V–
V
IN
+
V
OUT PUT
OPA336
Right Arm
Left Arm
OPA336
10kΩ
Shield
Drive 390kΩ
Shield
Right
Leg
V
R
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)
INA2331AIPWR ACTIVE TSSOP PW 14 2500 Green (RoHS
& no Sb/Br) CU NIPDAU Level-2-260C-1 YEAR
INA2331AIPWRG4 ACTIVE TSSOP PW 14 2500 Green (RoHS
& no Sb/Br) CU NIPDAU Level-2-260C-1 YEAR
INA2331AIPWT ACTIVE TSSOP PW 14 250 Green (RoHS
& no Sb/Br) CU NIPDAU Level-2-260C-1 YEAR
INA2331AIPWTG4 ACTIVE TSSOP PW 14 250 Green (RoHS
& no Sb/Br) CU NIPDAU Level-2-260C-1 YEAR
INA331AIDGKR ACTIVE VSSOP DGK 8 2500 Green (RoHS
& no Sb/Br) CU NIPDAUAGLevel-2-260C-1 YEAR
INA331AIDGKRG4 ACTIVE VSSOP DGK 8 2500 Green (RoHS
& no Sb/Br) CU NIPDAUAGLevel-2-260C-1 YEAR
INA331AIDGKT ACTIVE VSSOP DGK 8 250 Green (RoHS
& no Sb/Br) CU NIPDAUAGLevel-2-260C-1 YEAR
INA331AIDGKTG4 ACTIVE VSSOP DGK 8 250 Green (RoHS
& no Sb/Br) CU NIPDAUAGLevel-2-260C-1 YEAR
INA331IDGKR ACTIVE VSSOP DGK 8 2500 Green (RoHS
& no Sb/Br) CU NIPDAUAGLevel-2-260C-1 YEAR
INA331IDGKRG4 ACTIVE VSSOP DGK 8 2500 Green (RoHS
& no Sb/Br) CU NIPDAUAGLevel-2-260C-1 YEAR
INA331IDGKT ACTIVE VSSOP DGK 8 250 Green (RoHS
& no Sb/Br) CU NIPDAUAGLevel-2-260C-1 YEAR
INA331IDGKTG4 ACTIVE VSSOP DGK 8 250 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.
PACKAGE OPTION ADDENDUM
www.ti.com 16-Aug-2012
Addendum-Page 2
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.
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
INA2331AIPWR TSSOP PW 14 2500 330.0 12.4 6.9 5.6 1.6 8.0 12.0 Q1
INA2331AIPWT TSSOP PW 14 250 180.0 12.4 6.9 5.6 1.6 8.0 12.0 Q1
INA331AIDGKR VSSOP DGK 8 2500 330.0 12.4 5.3 3.4 1.4 8.0 12.0 Q1
INA331AIDGKT VSSOP DGK 8 250 180.0 12.4 5.3 3.4 1.4 8.0 12.0 Q1
INA331IDGKR VSSOP DGK 8 2500 330.0 12.4 5.3 3.4 1.4 8.0 12.0 Q1
INA331IDGKT VSSOP DGK 8 250 180.0 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)
INA2331AIPWR TSSOP PW 14 2500 367.0 367.0 35.0
INA2331AIPWT TSSOP PW 14 250 210.0 185.0 35.0
INA331AIDGKR VSSOP DGK 8 2500 367.0 367.0 35.0
INA331AIDGKT VSSOP DGK 8 250 210.0 185.0 35.0
INA331IDGKR VSSOP DGK 8 2500 367.0 367.0 35.0
INA331IDGKT VSSOP DGK 8 250 210.0 185.0 35.0
PACKAGE MATERIALS INFORMATION
www.ti.com 16-Aug-2012
Pack Materials-Page 2
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