INA321
INA2321
SBOS168D − DECEMBER 2000 − REVISED JANUARY 2006
microPower, Single-Supply, CMOS
Instrumentation Amplifier
FEATURES
APPLICATIONS
D LOW QUIESCENT CURRENT: 40µA/channel
D INDUSTRIAL SENSOR AMPLIFIERS:
D
D
D
D
D
D
D
D
D
Shut Down: < 1µA
HIGH GAIN ACCURACY: G = 5, 0.02%,
2ppm/°C
GAIN SET WITH EXTERNAL RESISTORS
LOW OFFSET VOLTAGE: ±200µV
HIGH CMRR: 94dB
LOW BIAS CURRENT: 10pA
BANDWIDTH: 500kHz, G = 5V/V
RAIL-TO-RAIL OUTPUT SWING: (V+) − 0.02V
WIDE TEMPERATURE RANGE:
−55°C to +125°C
SINGLE VERSION IN MSOP-8 PACKAGE AND
DUAL VERSION IN TSSOP-14 PACKAGE
Bridge, RTD, Thermistor, Position
D PHYSIOLOGICAL AMPLIFIERS:
D
D
D
D
D
D
D
ECG, EEG, EMG
A/D CONVERTER SIGNAL CONDITIONING
DIFFERENTIAL LINE RECEIVERS WITH GAIN
FIELD UTILITY METERS
PCMCIA CARDS
COMMUNICATION SYSTEMS
TEST EQUIPMENT
AUTOMOTIVE INSTRUMENTATION
CMRR vs FREQUENCY
120
DESCRIPTION
Configured internally for 5V/V gain, the INA321 offers
exceptional flexibility with user-programmable external
gain resistors. The INA321 reduces common-mode error
over frequency and with CMRR remaining high up to 3kHz,
line noise and line harmonics are rejected.
The low-power design does not compromise on bandwidth
or slew rate, making the INA321 ideal for driving sample
Analog-to-Digital (A/D) converters as well as
general-purpose applications. With high precision, low
cost, and small packaging, the INA321 outperforms
discrete designs, while offering reliability and
performance.
CMRR (dB)
100
The INA321 family is a series of rail-to-rail output,
micropower CMOS instrumentation amplifiers that offer
wide-range, single-supply, as well as bipolar-supply
operation. The INA321 family provides low-cost, low-noise
amplification of differential signals with micropower
current consumption of 40µA. When shutdown, the
INA321 has a quiescent current of less than 1µA.
Returning to normal operations within microseconds, the
shutdown feature makes the INA321 optimal for
low-power battery or multiplexing applications.
INA321
80
10x
Im provement
Nearest
Competition
60
40
10
100
1k
10k
Frequency (Hz)
R1
160kΩ
40kΩ
RG
40kΩ
R2
160kΩ
REF
A1
A3
VIN−
VOUT
A2
VIN+
Gain = 5 + 5(R2/R1)
V OUT = (VIN+ − VIN−) • Gain
Shutdown
V+
V−
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 2000-2006, Texas Instruments Incorporated
! !
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SBOS168D − DECEMBER 2000 − REVISED JANUARY 2006
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
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.
Operating Temperature . . . . . . . . . . . . . . . . . . . . . . −65°C to +150°C
Storage Temperature . . . . . . . . . . . . . . . . . . . . . . . . −65°C to +150°C
Junction Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . +150°C
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.
(1) Stresses above these ratings may cause permanent damage.
Exposure to absolute maximum conditions for extended periods
may degrade device reliability. These are stress ratings only, and
functional operation of the device at these or any other conditions
beyond those specified is not supported.
(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.
PACKAGE/ORDERING INFORMATION(1)
PACKAGE-LEAD
PACKAGE
DESIGNATOR
SPECIFIED
TEMPERATURE
RANGE
PACKAGE
MARKING
ORDERING
NUMBER
TRANSPORT
MEDIA, QUANTITY
SINGLE
INA321E
MSOP-8
DGK
−55°C to +125°C
C21
INA321E/250
INA321E/2K5
Tape and Reel, 250
Tape and Reel, 2500
INA321EA
MSOP-8
DGK
−55°C to +125°C
C21
INA321EA/250
INA321EA/2K5
Tape and Reel, 250
Tape and Reel, 3000
DUAL
INA2321EA
TSSOP-14
PW
−55°C to +125°C
INA2321EA
INA2321EA/250
INA2321EA/2K5
Tape and Reel, 250
Tape and Reel, 2500
PRODUCT
″
″
″
″
″
″
″
″
″
″
″
″
″
″
″
(1) For the most current package and ordering information, see the Package Option Addendum located at the end of this data sheet.
PIN CONFIGURATIONS
Top View
INA2321
INA321
RG
1
8
Shutdown
VIN−
2
7
V+
VIN+
3
6
VOUT
V−
4
5
REF
MSOP−8 (E, EA)
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
Dual, TSSOP−14 (EA)
2
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SBOS168D − DECEMBER 2000 − REVISED JANUARY 2006
ELECTRICAL CHARACTERISTICS: VS = +2.7V to +5.5V
BOLDFACE limits apply over the specified temperature range, TA = −555C to +1255C.
At TA = +25°C, RL = 25kΩ, G = 25, and IA common = VS/2, unless otherwise noted.
INA321EA
INA2321EA
INA321E
PARAMETER
CONDITIONS
MIN
TYP
MAX
±0.2
±0.5
MIN
TYP
MAX
UNIT
1
mV
INPUT
Input Offset Voltage, RTI
Over Temperature
VS = +5V
vs Temperature
VOS
dVOS/dT
vs Power Supply
PSRR
2.5
±7
±50
VS = +2.7V to +5.5V
*
±200
∗
±220
Over Temperature
Input Impedance
Input Common-Mode Range
CMRR
Over Temperature
mV
µV/°C
∗
*
±0.4
1013 || 3
Long-Term Stability
Common-Mode
Rejection
∗
±2.2
∗
µV/V
µV/V
µV/month
∗
Ω || pF
VS = 2.7V
VS = 5V
0.35
1.5
∗
∗
V
0.55
3.8
∗
∗
V
VS = 5V, VCM = 0.55V to 3.8V
90
VS = 5V, VCM = 0.55V to 3.8V
VS = 2.7V, VCM = 0.35V to 1.5V
77
Crosstalk, Dual
94
80
∗
dB
75
dB
94
∗
dB
110
∗
dB
INPUT BIAS CURRENT
Bias Current
IB
IOS
en
Offset Current
NOISE, RTI
±0.5
±10
∗
∗
pA
±0.5
±10
∗
∗
pA
RS = 0Ω
500
∗
nV/√Hz
f = 100Hz
190
∗
nV/√Hz
f = 1kHz
100
∗
nV/√Hz
f = 0.1Hz to 10Hz
20
∗
3
∗
µVPP
fA/√Hz
Voltage Noise: f = 10Hz
Current Noise: f = 1kHz
GAIN(1)
Gain Equation, Externally Set
G>5
Range of Gain
Nonlinearity
1000
∗
∗
V/V
±0.02
±0.1
∗
∗
%
G=5
±2
±10
*
*
ppm/°C
G = 25, VS = 5V, VO = 0.05 to 4.95
±0.001
±0.010
∗
∗
% of FS
±0.002
±0.015
*
*
% of FS
Gain Error
vs Temperature
∗
G = 5 + 5 (R2/R1)
5
Over Temperature
OUTPUT
Output Voltage Swing from Rail(2, 5)
Over Temperature
50
25
See Typical Characteristic(3)
+ISC
−ISC
∗
∗
*
50
Capacitance Load Drive
Short-Circuit Current
G ≥ 10
mV
mV
∗
pF
∗
mA
8
16
NOTE: ∗ Specification is same as INA321E.
(1) Does not include errors from external gain setting resistors.
(2) Output voltage swings are measured between the output and power-supply rails.
(3) See typical characteristic Percent Overshoot vs Load Capacitance.
(4) See typical characteristic Shutdown Voltage vs Supply Voltage.
(5) Output does not swing to positive rail if gain is less than 10.
3
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SBOS168D − DECEMBER 2000 − REVISED JANUARY 2006
ELECTRICAL CHARACTERISTICS: VS = +2.7V to +5.5V (continued)
BOLDFACE limits apply over the specified temperature range, TA = −555C to +1255C.
At TA = +25°C, RL = 25kΩ, G = 25, and IA common = VS/2, unless otherwise noted.
INA321EA
INA2321EA
INA321E
PARAMETER
CONDITIONS
MIN
TYP
MAX
MIN
TYP
MAX
UNIT
FREQUENCY RESPONSE
Bandwidth, −3dB
BW
G=5
500
∗
kHz
Slew Rate
SR
VS = 5V, G = 25
G = 5, CL = 50pF, VO = 2V step
0.4
∗
V/µs
Settling Time, 0.1%
tS
0.01%
Overload Recovery
50% Input Overload G = 25
8
∗
µs
12
∗
µs
2
∗
µs
POWER SUPPLY
Specified Voltage Range
+2.7
Operating Voltage Range
Quiescent Current
+5.5
IQ
per Channel, VSD > 2.5(4)
40
ISD
per Channel, VSD > 0.8(4)
0.01
Over Temperature
Shutdown Quiescent Current
∗
∗
V
∗
µA
*
µA
∗
µA
∗
+2.5 to +5.5
∗
60
70
∗
1
V
TEMPERATURE RANGE
Specified Range
−55
+125
∗
∗
°C
Operating/Storage Range
−65
+150
∗
∗
°C
Thermal Resistance
qJA
MSOP-8, TSSOP-14
Surface-Mount
150
NOTE: ∗ Specification is same as INA321E.
(1) Does not include errors from external gain setting resistors.
(2) Output voltage swings are measured between the output and power-supply rails.
(3) See typical characteristic Percent Overshoot vs Load Capacitance.
(4) See typical characteristic Shutdown Voltage vs Supply Voltage.
(5) Output does not swing to positive rail if gain is less than 10.
4
∗
°C/W
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SBOS168D − DECEMBER 2000 − REVISED JANUARY 2006
TYPICAL CHARACTERISTICS
At TA = +25°C, VS = 5V, VCM =1/2VS, RL = 25kΩ, and CL = 50pF, unless otherwise noted.
COMMON−MODE REJECTION RATIO
vs FREQUENCY
GAIN vs FREQUENCY
120
80
70
60
100
Gain = 500
50
80
CMRR (dB)
Gain = 100
Gain (dB)
40
Gain = 25
30
20
Gain = 5
10
0
60
40
20
−10
−20
0
10
100
1k
10k
100k
1M
10
10M
100
POWER−SUPPLY REJECTION RATIO
vs FREQUENCY
6
Maximum Output Voltage (VPP)
90
80
PSRR (dB)
70
60
50
40
30
20
10
100k
VS = 5.5V
5
VS = 5.0V
4
VS = 2.7V
3
2
1
0
0
10
1
100
1k
10k
100
100k
Frequency (Hz)
1k
10
100
1
10
100
1k
10k
100k
1M
10M
10k
0.1
100k
0.1Hz TO 10Hz VOLTAGE NOISE
10µv/div
100
INoise (fA/√Hz)
10k
10
1k
Frequency (Hz)
NOISE vs FREQUENCY
VNOISE (nV/√Hz)
10k
MAXIMUM OUTPUT VOLTAGE vs FREQUENCY
100
1
1k
Frequency (Hz)
Frequency (Hz)
1s/div
Frequency (Hz)
5
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TYPICAL CHARACTERISTICS (continued)
At TA = +25°C, VS = 5V, VCM =1/2VS, RL = 25kΩ, and CL = 50pF, unless otherwise noted.
COMMON−MODE INPUT RANGE
vs REFERENCE VOLTAGE
OUTPUT SWING vs LOAD RESISTANCE
25
OutputReferred to Ground (V)
6
15
To Positive Rail
10
To Negative Rail
5
5
Outside of Normal Operation
4
3
REF
Increasing
2
1
0
0
0
20k
40k
60k
80k
100k
1
0
RLOAD (Ω)
QUIESCENT CURRENT AND SHUTDOWN CURRENT
vs POWER SUPPLY
500
45
450
350
300
25
250
20
200
15
150
10
IQ (µA)
30
ISD (nA)
IQ (µA)
400
IQ
35
100
ISD
5
50
0
0
2.5
3
3.5
4
3
4
5
QUIESCENT CURRENT AND SHUTDOWN CURRENT
vs TEMPERATURE
50
40
2
Input Common−Mode Voltage (V)
4.5
5
60
55
50
45
40
35
30
25
20
15
10
5
0
600
500
300
200
100
ISD
−75
5.5
400
IQ
−50
−25
0
25
50
75
100
125
0
150
Temperature (_C)
Supply Voltage (V)
SHORT−CIRCUIT CURRENT vs TEMPERATURE
SHORT−CIRCUIT CURRENT vs POWER SUPPLY
20
30
25
ISC+
15
10
ISC (mA)
ISC (mA)
20
ISC−
ISC+
15
10
5
ISC−
5
0
0
2.5
3
3.5
4
4.5
Supply Voltage (V)
6
5
5.5
−75
−50
−25
0
25
50
75
Temperature (_ C)
100
125
150
ISD (nA)
Swing−to−Rail (mV)
20
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TYPICAL CHARACTERISTICS (continued)
At TA = +25°C, VS = 5V, VCM =1/2VS, RL = 25kΩ, and CL = 50pF, unless otherwise noted.
SMALL−SIGNAL STEP RESPONSE (G = 100)
50mV/div
100mV/div
SMALL−SIGNAL STEP RESPONSE (G = 5)
50µs/div
SMALL−SIGNAL STEP RESPONSE
(G = 5, CL = 1000pF)
SMALL−SIGNAL STEP RESPONSE
(G = 100, CL = 1000pF)
50mV/div
100mV/div
10µs/div
50µs/div
SMALL−SIGNAL STEP RESPONSE
(G = 100, CL = 5000pF)
LARGE−SIGNAL STEP RESPONSE
(G = 25, CL = 50pF)
1V/div
50mV/div
10µs/div
50µs/div
50µs/div
7
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SBOS168D − DECEMBER 2000 − REVISED JANUARY 2006
TYPICAL CHARACTERISTICS (continued)
At TA = +25°C, VS = 5V, VCM =1/2VS, RL = 25kΩ, and CL = 50pF, unless otherwise noted.
PERCENT OVERSHOOT vs LOAD CAPACITANCE
SETTLING TIME vs GAIN
60
100
Output 2VPP
Differential
Input Drive
Settling Time (µs)
80
Output 100mVPP
Differential
Input Drive
50
70
Overshoot (%)
90
0.01%
60
50
40
30
G=5
40
30
G = 25
20
0.1%
20
10
10
0
0
1
10
100
10
1000
100
10k
Load Capacitance (pF)
SHUTDOWN VOLTAGE vs SUPPLY VOLTAGE
SHUTDOWN TRANSIENT BEHAVIOR
3
Operation in this Region
is not Recommended
2.5
Normal Operation Mode
VSD
2
1V/div
Shutdown (V)
1k
Gain (V/V)
1.5
1
VOUT
Shutdown Mode
0.5
Part Draws Below 1µA Quiescent Current
0
2.3
3
3.5
4
4.5
5
5.5
50µs/div
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
Offset Voltage (mV)
8
Offset Voltage Drift (µV/_C)
20
18
16
14
12
8
10
6
4
2
0
−2
−4
−6
−8
−1 0
−1 2
−1 4
−1 6
−1 8
−2 0
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0
0.1
− 0.1
− 0.2
− 0.3
− 0.4
− 0.5
− 0.6
− 0.7
− 0.8
− 0.9
0
− 1.0
0
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SBOS168D − DECEMBER 2000 − REVISED JANUARY 2006
TYPICAL CHARACTERISTICS (continued)
At TA = +25°C, VS = 5V, VCM =1/2VS, RL = 25kΩ, and CL = 50pF, unless otherwise noted.
INPUT BIAS CURRENT vs TEMPERATURE
10k
0.8
1k
Input Bias Current (pA)
Slew Rate (V/µs)
SLEW RATE vs TEMPERATURE
1
0.6
0.4
0.2
0
−75
−50
100
10
0
0.1
−25
0
25
50
75
100
125
150
− 75
− 50
− 25
0
Temperature (_C)
CROSSTALK vs FREQUENCY
50
75
100
125
150
OUTPUT VOLTAGE SWING vs OUTPUT CURRENT
5
120
100
4
Output Voltage (V)
Crosstalk (dB)
25
Temperature (_ C)
80
60
40
+125°C
− 55_ C
+25°C
3
2
+125°C
− 55_ C
+25°C
1
20
0
0
0.1
1
10
100
1k
Frequency (Hz)
10k
100k
1M
0
2
4
6
8
10
12
14
16
18
20
22
24
Output Current (mA)
9
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SBOS168D − DECEMBER 2000 − REVISED JANUARY 2006
APPLICATIONS INFORMATION
The INA321 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 INA321 and INA2321. The power supply should be
capacitively decoupled with 0.1µF capacitors as close to
the INA321 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 INA321 family is fully specified over a supply range of
+2.7V to +5.5V, with key parameters assured 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 INA321 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
RG
1
REF
5
160kΩ
40kΩ
R2
R1
OPEN SHORT
100kΩ 100kΩ
10kΩ
90kΩ
10kΩ 190kΩ
5
10
50
100
160kΩ
VIN−
2
VIN+
3
40kΩ
A1
A3
6
VO = ((VIN+) − (VIN −)) • G
A2
Also drawn in simplified form:
8
Shutdown
4
7
VIN+
(For Single
Supply)
0.1µF
V+
7
5
INA321
0.1µF
REF
V+
Shutdown
3
V−
VIN−
2
8
6
1
4
V−
RG
Figure 1. Basic Connections
+5V
Bridge
Sensor
VIN+
3
V+
7
REF(1)
5
INA321
VIN−
Shutdown
8
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. Bridge Amplifier of the INA321
10
VOUT
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SETTING THE GAIN
The ratio of R2 to R1, or the impedance between pins 1, 5,
and 6, determines the gain of the INA321. With an
internally set gain of 5, the INA321 can be programmed for
gains greater than 5 according to the following equation:
Figure 3 shows how bias current path can be provided in
the cases of microphone applications, thermistor
applications, ground returns, and dc-coupled resistive
bridge applications.
G = 5 + 5 (R2/R1)
The INA321 is designed to provide accurate gain, with gain
error assured to be less than 0.1%. Setting gain with
matching TC resistors will minimize gain drift. Errors from
external resistors will add directly to the gain error, and
may become dominant error sources.
V+
VIN + 3
8
Microphone,
Hydrophone,
etc.
REF
5
VIN− 2
INPUT COMMON-MODE RANGE
47kΩ
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:
VOA1 = 5/4 VCM — 1/4 VREF
INA321
V+
VIN +
RG
Shutdown
3
7
5
INA321
8
Transformer
REF
6
VOUT
1
VIN− 2
4
V−
REFERENCE
For optimal operation, VOA2 should be less than
VDD − 1.2V.
VOUT
4
V−
VB(1)
VOA2 = VREF + 5 (VIN+ − VIN−)
6
1
VB (1)
(See Typical Characteristics for Input Common-Mode
Range vs Reference Voltage).
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:
Shutdown
7
Bridge
Amplifier
Center−tap
RG provides bias
current return
VEX
V+
Bridge
Sensor
VIN +
Shutdown
3
7
5
INA321
8
REF
6
VOUT
1
VIN− 2
4
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).
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 INA321 is ideal
for use with high-impedance sources. The input bias
current of less than 10pA makes the INA321 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. Providing an Input Common-Mode Path
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.
11
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SBOS168D − DECEMBER 2000 − REVISED JANUARY 2006
OUTPUT BUFFERING
The INA321 is optimized for a load impedance of 10kΩ or
greater. For higher output current the INA321 can be
buffered using the OPA340, as shown in Figure 4. The
OPA340 can swing within 50mV of the supply rail, driving
a 600Ω load. The OPA340 is available in the tiny MSOP-8
package.
low output impedance at high frequencies makes it
suitable for directly driving Capacitive Digital-to-Analog
(CDAC) input A/D converters, as shown in Figure 5.
+5V
VIN+
REF
VIN−
0.1µF
VIN +
REF
VIN−
3
5
INA321
6
6
VOUT
ADS7818
or
ADS7822
1
2
4
V−
12−Bits
RG
fS < 100kHz
OPA340
VOUT
4
V−
INA321
VOUT
1
2
5
Shutdown
0.1µF
Shutdown
8
V+
7
8
+5V
V+
7
3
RG
Figure 4. Output Buffering Circuit. Able to drive
loads as low as 600Ω.
SHUTDOWN MODE
The shutdown pin of the INA321 is nominally connected to
V+. When the pin is pulled below 0.8V on a 5V supply, the
INA321 goes into sleep mode within nanoseconds. For
actual shutdown threshold, see the Typical Characteristic
curve, Shutdown Voltage vs Supply Voltage. Drawing less
than 1µA 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 INA321 suitable for
multiplexing.
Figure 5. INA321 Directly Drives a
Capacitive-Input, A/D Converter
OFFSET TRIMMING
The INA321 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.
V+
VIN+
REF(1) 5
VIN−
8
INA321
6
VOUT
1
2
4
RAIL-TO-RAIL OUTPUT
V−
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 25kΩ, the output
voltage can swing to within a few millivolts of the supply rail
while maintaining low gain error. For heavier loads and
over temperature, see the Typical Characteristic curve,
Output Voltage Swing vs Output Current. The INA321’s
Shutdown
7
3
OPA336
RG
Adjustable
Voltage
NOTE: (1) REF should be adjusted for the desired output level.
The value of REF affects the common−mode input range.
Figure 6. Optional Offset Trimming Voltage
12
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SBOS168D − DECEMBER 2000 − REVISED JANUARY 2006
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.
V+
RLIM
3
VIN+
IOVERLOAD
10mA max
REF
5
7
INA321
VOUT
1
2
VIN−
6
4
RLIM
V−
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
Shutdown
8
Calculation of the worst-case expected offset would be as
follows:
RG
Figure 7. Input Protection
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 INA321’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.
OFFSET VOLTAGE ERROR CALCULATION
The offset voltage (VOS) of the INA321E is specified at a
maximum of 500µV with a +5V power supply and the
common-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 INA321, 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:
V+
VIN +
7
3
Shutdown
8
INA321
REF
6
5
VOUT
CIN
CL
1
VIN−
RX
2
4
RG
V−
RIN
RF
RIN • CIN = RF • CF
CF
CMRR (in µV/V) = 10[(CMRR in dB)/—20] • 106
For the INA321, 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.
Where CIN is equal to the INA321 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:
RIN • CIN = RF • CF
where CIN is equal to the INA321’s RG-pin input
capacitance (typically 3pF) plus the layout capacitance.
The capacitor can be varied until optimum performance is
obtained.
13
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SBOS168D − DECEMBER 2000 − REVISED JANUARY 2006
APPLICATION CIRCUITS
Medical ECG Applications
optional right leg drive. Filtering can be modified to suit
application needs by changing the capacitor value of the
output filter.
Figure 9 shows the INA321 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
Low-Power, Single-Supply Data Acquisition
Systems
Refer to Figure 5 to see the INA321 configured to drive an
ADS7818. Functioning at frequencies of up to 500kHz, the
INA321 is ideal for low-power data acquisition.
VR
OPA336
1.6nF
0.1µF
V+
100kΩ
Left Arm
VIN+ 3
Shield
100kΩ
Right Arm
REF
5
VIN−
2
Shutdown
7
8
INA321
1
V−
2MΩ
10kΩ
OPA336
RG
1MΩ
2MΩ
Shield
Drive
10kΩ
390kΩ
OPA336
100kΩ
OPA336
VR
Figure 9. Simplified ECG Circuit for Medical Applications
14
VOUT PUT
VR
2kΩ
VR = +2.5V
2kΩ
10kΩ
6
4
+5V
1MΩ
1MΩ
Right
Leg
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)
INA2321EA/250
ACTIVE
TSSOP
PW
14
250
RoHS & Green
NIPDAU
Level-1-260C-UNLIM
INA2321EA/2K5
ACTIVE
TSSOP
PW
14
2500
RoHS & Green
NIPDAU
Level-1-260C-UNLIM
INA321E/250
ACTIVE
VSSOP
DGK
8
250
RoHS & Green
Call TI
Level-2-260C-1 YEAR
INA321E/250G4
ACTIVE
VSSOP
DGK
8
250
RoHS & Green
Call TI
INA321E/2K5
ACTIVE
VSSOP
DGK
8
2500
RoHS & Green
INA321EA/250
ACTIVE
VSSOP
DGK
8
250
INA321EA/250G4
ACTIVE
VSSOP
DGK
8
INA321EA/2K5
ACTIVE
VSSOP
DGK
8
-55 to 125
INA
2321EA
Samples
INA
2321EA
Samples
-55 to 125
C21
Samples
Level-2-260C-1 YEAR
-55 to 125
C21
Samples
Call TI
Level-2-260C-1 YEAR
-55 to 125
C21
Samples
RoHS & Green
Call TI
Level-2-260C-1 YEAR
-55 to 125
C21
Samples
250
RoHS & Green
Call TI
Level-2-260C-1 YEAR
-55 to 125
C21
Samples
2500
RoHS & Green
Call TI
Level-2-260C-1 YEAR
-55 to 125
C21
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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