INA3
31
INA
233
1
INA331
INA2331
®
SBOS215C – DECEMBER 2001 – REVISED APRIL 2005
Low-Power, Single-Supply, CMOS
INSTRUMENTATION AMPLIFIERS
FEATURES
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
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
DESCRIPTION
The INA331 rejects line noise and its harmonics, because
common-mode error remains low even at higher frequencies.
The INA331 and INA2331 are rail-to-rail output, low-power
CMOS instrumentation amplifiers that offer wide range, singlesupply 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.
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.
Configured internally in a gain of 5V/V, the INA331 offers
flexibility in higher gains by choosing external resistors.
R2
R1
RG
G = 5 + (5R2/R1)
INA2331
40kΩ
INA331
10kΩ
VREF
40kΩ
Ch A
10kΩ
A1
A3
VOUT
A2
VIN–
Ch B
VIN+
V+
V–
Shutdown
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.
All trademarks are the property of their respective owners.
Copyright © 2001-2005, Texas Instruments Incorporated
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.
www.ti.com
ELECTROSTATIC
DISCHARGE SENSITIVITY
ABSOLUTE MAXIMUM RATINGS(1)
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
This integrated circuit can be damaged by ESD. Texas Instruments recommends that all integrated circuits be handled with
appropriate precautions. Failure to observe proper handling
and installation procedures can cause damage.
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.
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.
PACKAGE/ORDERING INFORMATION(1)
PRODUCT
PACKAGE-LEAD
PACKAGE
DESIGNATOR
PACKAGE
MARKING
Single
INA331IDGK
INA331AIDGK
MSOP-8
MSOP-8
DGK
DGK
C31
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.
PIN CONFIGURATION
Top View
INA2331
RGA
1
14
Shutdown A
VIN–A
2
13
VOUTA
VIN+A
3
12
REFA
V–
4
11
V+
VIN+B
5
10
REFB
VIN–B
6
9
VOUTB
RGB
7
8
Shutdown B
INA331
RG
1
8
Shutdown
VIN–
2
7
V+
VIN+
3
6
VOUT
V–
4
5
REF
MSOP-8 (DGK)
Dual, TSSOP-14 (PW)
2
INA331, INA2331
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SBOS215C
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
INA2331AIPW
INA331IDGK
PARAMETER
INPUT
Input Offset Voltage, RTI
Over Temperature
Temperature Coefficient
vs Power Supply
vs Temperature
Long-Term Stability
Input Impedance
Input Common-Mode Range
Common-Mode Rejection
–40°C to +85°C
Over Temperature
CONDITION
VOS
dVOS/dT
PSRR
MIN
TYP
MAX
VS = +5V
±250
VS = +2.7V to +5.5V
±5
±50
±500
±1.7
CMRR
0.35
0.55
90
77
72
1.5
3.8
94
✻
✻
80
75
70
VCM = VS /2
±0.5
±0.5
IOS
NOISE, RTI
Voltage Noise: f = 10Hz
f = 100Hz
f = 1kHz
f = 0.1Hz to 10Hz
Current Noise: f = 1kHz
UNITS
✻
±1000
±2.1
µV
mV
µV/°C
µV/V
µV/V
µV/month
Ω || pF
V
V
dB
dB
dB
dB
dB
✻
✱
✻
✻
✻
✻
114
94
IB
MAX
✻
✻
Crosstalk, Dual
INPUT BIAS CURRENT
Bias Current
Offset Current
TYP
✱
✻
±200
±220
±0.4
1013 || 3
VS = 2.7V
VS = 5V
VS = 5V, VCM = 0.55V to 3.8V
VS = 5V, VCM = 0.55V to 3.8V
VS = 5V, VCM = 0.55V to 3.8V
VS = 2.7V, VCM = 0.35V to 1.5V
MIN
±10
±10
✻
✻
✻
✻
pA
pA
RS = 0Ω
eN
iN
GAIN(1)
Gain Equation, Externally Set
Range of Gain
Gain Error
vs Temperature
Nonlinearity
Over Temperature
G>5
±0.02
±2
±0.001
±0.002
G=5
G=5
G = 25(2), VS = 5V, VO = 0.05 to 4.95
RL = 10kΩ
G > 10
nV/√Hz
nV/√Hz
nV/√Hz
µVPP
fA/√Hz
✻
G = 5 + (5R2/R1)
5
OUTPUT
Output Voltage Swing from Rail(3)
Over Temperature
Capacitance Load Drive
Short-Circuit Current
✻
✻
✻
✻
✻
280
96
46
7
0.5
1000
±0.1
±10
±0.010
±0.015
50
25
50
See Typical Characteristics
+48/–32
✻
✻
✱
✻
✱
✻
✱
✻
✻
✱
✻
✱
✻
V/V
%
ppm/°C
% of FS
% of FS
✻
✻
mV
mV
pF
mA
✻
✻
✻
✻
✻
MHz
V/µs
µs
µs
µs
FREQUENCY RESPONSE
Bandwidth, –3dB
Slew Rate
Settling Time, 0.1%
0.01%
Overload Recovery
POWER SUPPLY
Specified Voltage Range
Operating Voltage Range
Quiescent Current per Channel
Over Temperature
Shutdown Quiescent Current/Chan
TEMPERATURE RANGE
Specified/Operating Range
Storage Range
Thermal Resistance
BW
SR
tS
G = 25
VS = 5V, G = 25
G = 25, CL = 100pF, VO = 2V step
2.0
5
1.7
2.5
2
50% Input Overload G = 25
+2.7
+5.5
IQ
VSD > 2.5(3)
+2.5 to +5.5
415
ISD
VSD < 0.8(3)
0.01
–55
–65
θJA MSOP-8, TSSOP-14 Surface Mount
✻
✻
✻
490
600
1
+125
+150
150
✻
✻
✻
✻
✻
✱
✻
✻
✻
✻
V
V
µA
µA
µA
°C
°C
°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
www.ti.com
3
TYPICAL CHARACTERISTICS
At TA = +25°C, VS = 5V, VCM = VS /2, RL = 10kΩ, and CL = 100pF, unless otherwise noted.
COMMON-MODE REJECTION RATIO
vs FREQUENCY
GAIN vs FREQUENCY
80
120
70
60
50
80
Gain = 100
CMRR (dB)
Gain (dB)
100
Gain = 500
40
Gain = 25
30
20
Gain = 5
10
0
60
40
20
–10
–20
0
10
100
1k
10k
100k
1M
10M
10
100
Frequency (Hz)
POWER-SUPPLY REJECTION RATIO
vs FREQUENCY
Maximum Output Voltage (VPP)
90
80
70
PSRR (dB)
10k
100k
MAXIMUM OUTPUT VOLTAGE vs FREQUENCY
6
100
60
50
40
30
20
10
0
VS = 5.5V
5
VS = 5.0V
4
3
VS = 2.7V
2
1
0
1
10
100
1k
10k
100
100k
10
100
1
10
100
1k
100k
1M
10M
10k
0.1
100k
2µV/div
1k
INOISE (fA/√Hz)
100
10
10k
0.1Hz TO 10Hz VOLTAGE NOISE
NOISE vs FREQUENCY
10k
1
1k
Frequency (Hz)
Frequency (Hz)
VNOISE (nV/√Hz)
1k
Frequency (Hz)
1s/div
Frequency (Hz)
4
INA331, INA2331
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SBOS215C
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
OUTPUT SWING vs LOAD RESISTANCE
6
Output—Referred to Ground (V)
25
Swing-to-Rail (mV)
20
15
To Positive Rail
10
To Negative Rail
5
5
Outside of Normal Operation
4
3
2
1
0
0
0
10k
20k
30k
40k
0
50k
2
5
QUIESCENT CURRENT AND SHUTDOWN CURRENT
vs POWER SUPPLY
QUIESCENT CURRENT AND SHUTDOWN CURRENT
vs TEMPERATURE
IQ
400
350
IQ (µA)
300
250
200
150
100
ISD
50
0
3
3.5
4
4.5
5
600
550
500
450
400
350
300
250
200
150
100
50
0
IQ
ISD
–75
5.5
–50
–25
0
25
50
75
100
125
150
Temperature (°C)
Supply Voltage (V)
SHORT-CIRCUIT CURRENT vs POWER SUPPLY
SHORT-CIRCUIT CURRENT vs TEMPERATURE
60
60
ISC+
ISC+
50
50
40
40
ISC–
ISC (mA)
ISC (mA)
4
3
Input Common-Mode Voltage (V)
450
2.5
1
RLOAD (Ω)
500
IQ (µA), ISD (nA)
REF
Increasing
30
ISC–
30
20
20
10
10
0
0
2.5
3
3.5
4
4.5
5
5.5
–75
Supply Voltage (V)
–25
0
25
50
75
100
125
150
Temperature (°C)
INA331, INA2331
SBOS215C
–50
www.ti.com
5
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 = 100)
50mV/div
100mV/div
SMALL-SIGNAL STEP RESPONSE (G = 5)
4µs/div
SMALL-SIGNAL STEP RESPONSE
(G = 5, CL = 1000pF)
SMALL-SIGNAL STEP RESPONSE
(G = 100, CL = 1000pF)
50mV/div
100mV/div
4µs/div
10µs/div
SMALL-SIGNAL STEP RESPONSE
(G = 100, CL = 4700pF)
LARGE-SIGNAL STEP RESPONSE (G = 25)
1V/div
50mV/div
4µs/div
10µs/div
6
10µs/div
INA331, INA2331
www.ti.com
SBOS215C
TYPICAL CHARACTERISTICS (Cont.)
At TA = +25°C, VS = 5V, VCM = VS /2, RL = 10kΩ, and CL = 100pF, unless otherwise noted.
PERCENT OVERSHOOT vs LOAD CAPACITANCE
SETTLING TIME vs GAIN
100
60
Output 2VPP
Differential
Input Drive
Output 100mVPP
Differential Drive
90
80
40
Overshoot (%)
Settling Time (µs)
50
0.01%
30
20
G=5
70
60
50
40
G = 25
30
10
20
0.1%
10
0
0
1
10
100
10
1k
100
1k
Gain (V/V)
Load Capacitance (pF)
SHUTDOWN VOLTAGE vs SUPPLY VOLTAGE
SHUTDOWN TRANSIENT BEHAVIOR
10k
3
Operation in this Region
is not Recommended
2.5
VSD
2
1V/div
Shutdown (V)
Normal Operation Mode
1.5
1
Shutdown Mode
VOUT
0.5
Part Draws Below 1µA Quiescent Current
0
2.5
3
3.5
4
4.5
5
50µs/div
5.5
Supply Voltage (V)
OFFSET VOLTAGE DRIFT
PRODUCTION DISTRIBUTION
OFFSET VOLTAGE PRODUCTION DISTRIBUTION
25
20
Percentage of Amplifiers (%)
Percentage of Amplifiers (%)
18
20
15
10
5
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
–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
0
Offset Voltage (µV/°C)
Offset Voltage (mV)
INA331, INA2331
SBOS215C
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7
TYPICAL CHARACTERISTICS (Cont.)
At TA = +25°C, VS = 5V, VCM = VS /2, RL = 10kΩ, and CL = 100pF, unless otherwise noted.
SLEW RATE vs TEMPERATURE
INPUT BIAS CURRENT vs TEMPERATURE
8
10000
Input Bias Current (pA)
7
Slew Rate (V/µs)
6
5
4
3
2
1000
100
10
1
1
0
0.1
–75
–50
–25
0
25
50
75
100
125
150
–75
–50
–25
0
Temperature (°C)
CHANNEL SEPARATION vs FREQUENCY
75
100
125
150
5
100
4
Output Voltage (V)
Separation (dB)
50
OUTPUT VOLTAGE SWING vs OUTPUT CURRENT
120
80
60
40
3
25°C
125°C
–55°C
2
1
20
0
0
1
10
100
1k
10k
100k
1M
10M
0
Frequency (Hz)
8
25
Temperature (°C)
5
10
15
20
25
30
35
40
45
50
55
60
Output Current (mA)
INA331, INA2331
www.ti.com
SBOS215C
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 capacitively 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 temperature range of –55°C to +125°C. Parameters that vary significantly 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.
G = 5 + 5 (R2 / R1 )
Short VOUT to RG
for G = 5
R1
DESIRED GAIN
(V/V)
R2
5
10
50
100
RG
1
5
REF
40kΩ
10kΩ
R2
R1
OPEN SHORT
100kΩ 100kΩ
10kΩ
90kΩ
10kΩ 190kΩ
40kΩ
VIN–
VIN+
10kΩ
A1
2
A3
6
VO = ((VIN+) – (VIN –)) • G
A2
3
Also drawn in simplified form:
8
4
7
Shutdown
VIN+
(For Single
Supply)
0.1µF
V+
7
5
INA331
0.1µF
8
REF
V–
V+
Shutdown
3
VIN–
2
6
VOUT
1
4
V–
RG
FIGURE 1. Basic Connections.
+5V
Bridge
Sensor
VIN+
3
V+
7
REF(1)
5
INA331
Shutdown
8
VIN–
6
VOUT
1
2
4
V–
RG
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.
FIGURE 2. Single-Supply Bridge Amplifier.
INA331, INA2331
SBOS215C
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9
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.
how the bias current path can be provided in the cases of
microphone applications, thermistor applications, ground returns, 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 balanced input. The advantages are lower input offset voltage
due to bias current flowing through the source impedance
and better high-frequency gain.
V+
VIN+ 3
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 performance. The lower limit of the input range is bounded by the
output swing of amplifier A1, and is a function of the reference voltage according to the following equation:
Shutdown
7
8
Microphone,
Hydrophone,
etc.
REF
5
VIN– 2
47kΩ
VB
INA331
6
VOUT
1
4
V–
RG
(1)
VOA1 = 5/4 VCM – 1/4 VREF
V+
VIN+ 3
(See typical characteristics Common-Mode Input Range vs
Reference Voltage.)
Shutdown
7
8
Transformer
REF
5
INA331
VIN– 2
REFERENCE
6
VOUT
1
4
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–)
VB(1)
Bridge
Amplifier
V–
VEX
V+
For ensured operation, V OA2 should be less than
VDD – 1.2V.
Bridge
Sensor
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 compensate 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).
Center-tap
RG provides bias
current return
VIN+ 3
Shutdown
7
8
REF
5
INA331
6
VOUT
1
VIN– 2
4
V–
RG Bridge resistance
provides bias
current return
NOTE: (1) VB is bias voltage within
common-mode range, dependent
on REF.
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
10
FIGURE 3. Providing an Input Common-Mode Path.
INA331, INA2331
www.ti.com
SBOS215C
SHUTDOWN MODE
+5V
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 shutdown threshold, see the typical characteristic Shutdown Voltage 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 ‘sleepmode’ the amplifier has high output impedance, making the
INA331 suitable for multiplexing.
0.1µF
VIN+
3
V+
7
5
INA331
8
REF
VIN–
0.1µF
Shutdown
6
VOUT
1
2
OPA340
VOUT
4
V–
RG
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 maintaining 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 CapacitiveInput A/D converters, as shown in Figure 4.
FIGURE 5. Output Buffering Circuit. Able to drive loads as
low as 600Ω.
V+
VIN+
7
5
INA331
8
REF(1)
V+
7
3
8
REF
VIN–
5
INA331
2
1
4
V–
6
VOUT
Adjustable
Voltage
12-Bits
NOTE: (1) REF should be adjusted for the desired output level.
The value of REF affects the common-mode input range.
RG
FIGURE 6. Optional Offset Trimming Voltage.
fS < 100kHz
INPUT PROTECTION
FIGURE 4. INA331 Directly Drives Capacitive-Input, HighSpeed 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 buffered 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.
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.
V+
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 commonmode rejection.
RLIM
3
VIN+
IOVERLOAD
10mA max
REF
5
Shutdown
7
8
INA331
6
VOUT
1
2
VIN–
4
RLIM
V–
RG
FIGURE 7. Sample Output Buffering Circuit.
INA331, INA2331
SBOS215C
RG
OPA336
ADS7818
or
ADS7822
VOUT
4
V–
Shutdown
6
1
2
VIN–
+5V
VIN+
Shutdown
3
www.ti.com
11
OFFSET VOLTAGE ERROR CALCULATION
FEEDBACK CAPACITOR IMPROVES RESPONSE
The offset voltage (VOS) of the INA331IDGK is specified at a
maximum of 500µV with a +5V power supply and the common-mode voltage at VS/2. Additional specifications for powersupply 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.
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 highfrequency noise.
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]
•
V+
VIN+
106
7
3
Shutdown
8
INA331
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 conditions. For example, an application might configure the amplifier with a 3.3V supply with 1V common-mode. This configuration 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:
REF
RX
6
5
VOUT
CIN
CL
1
VIN–
2
4
RG
V–
RIN
RF
RIN • CIN = RF • CF
CF
Where CIN is equal to the INA331’s input capacitance
(approximately 3pF) plus any parastic layout capacitance.
FIGURE 8. Feedback Capacitor Improves Dynamic Performance.
It is suggested that a variable capacitor be used for the
feedback capacitor since input capacitance may vary between 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:
Adjusted VOS = Maximum specified VOS +
(power-supply variation) • PSRR +
(common-mode variation) • CMRR
VOS = 0.5mV + (1.7V • 200µV) + (0.65V • 30µV)
= ±0.860mV
RIN • CIN = RF • CF
However, the typical value will be smaller, as seen in the
Typical Characteristics.
12
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.
INA331, INA2331
www.ti.com
SBOS215C
APPLICATION CIRCUITS
Filtering can be modified to suit application needs by changing the capacitor value of the output filter.
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.
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.
VR
OPA336
1.6nF
0.1µF
V+
100kΩ
Left Arm
VIN+ 3
Shield
100kΩ
Right Arm
8
REF
5
VIN–
2
INA331
10kΩ
1
V–
2MΩ
1MΩ
6
OPA336
10kΩ
VOUT PUT
VR
4
+5V
1MΩ
Shutdown
7
RG
1MΩ
2MΩ
2kΩ
VR = +2.5V
Shield
Drive
10kΩ
390kΩ
OPA336
2kΩ
OPA336
VR
Right
Leg
FIGURE 9. Simplified ECG Circuit for Medical Applications.
INA331, INA2331
SBOS215C
www.ti.com
13
PACKAGE OPTION ADDENDUM
www.ti.com
14-Oct-2022
PACKAGING INFORMATION
Orderable Device
Status
(1)
Package Type Package Pins Package
Drawing
Qty
Eco Plan
(2)
Lead finish/
Ball material
MSL Peak Temp
Op Temp (°C)
Device Marking
(3)
Samples
(4/5)
(6)
INA2331AIPWR
ACTIVE
TSSOP
PW
14
2500
RoHS & Green
NIPDAU
Level-2-260C-1 YEAR
-55 to 125
INA
2331A
Samples
INA2331AIPWT
ACTIVE
TSSOP
PW
14
250
RoHS & Green
NIPDAU
Level-2-260C-1 YEAR
-55 to 125
INA
2331A
Samples
INA331AIDGKR
ACTIVE
VSSOP
DGK
8
2500
RoHS & Green
Call TI
Level-2-260C-1 YEAR
-55 to 125
C31
Samples
INA331AIDGKT
ACTIVE
VSSOP
DGK
8
250
RoHS & Green
Call TI
Level-2-260C-1 YEAR
-55 to 125
C31
Samples
INA331AIDGKTG4
ACTIVE
VSSOP
DGK
8
250
RoHS & Green
Call TI
Level-2-260C-1 YEAR
-55 to 125
C31
Samples
INA331IDGKR
ACTIVE
VSSOP
DGK
8
2500
RoHS & Green
Call TI
Level-2-260C-1 YEAR
-55 to 125
C31
Samples
INA331IDGKT
ACTIVE
VSSOP
DGK
8
250
RoHS & Green
Call TI
Level-2-260C-1 YEAR
-55 to 125
C31
Samples
INA331IDGKTG4
ACTIVE
VSSOP
DGK
8
250
RoHS & Green
Call TI
Level-2-260C-1 YEAR
-55 to 125
C31
Samples
(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)
RoHS: TI defines "RoHS" to mean semiconductor products that are compliant with the current EU RoHS requirements for all 10 RoHS substances, including the requirement that RoHS substance
do not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, "RoHS" products are suitable for use in specified lead-free processes. TI may
reference these types of products as "Pb-Free".
RoHS Exempt: TI defines "RoHS Exempt" to mean products that contain lead but are compliant with EU RoHS pursuant to a specific EU RoHS exemption.
Green: TI defines "Green" to mean the content of Chlorine (Cl) and Bromine (Br) based flame retardants meet JS709B low halogen requirements of
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