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INA818
SBOS894A – APRIL 2019 – REVISED JUNE 2019
INA818 35-μV Offset, 8-nV/√Hz Noise, Low-Power, Precision Instrumentation Amplifier
1 Features
3 Description
•
•
The INA818 is a high-precision instrumentation
amplifier that offers low power consumption and
operates over a very wide single-supply or dualsupply range. A single external resistor sets any gain
from 1 to 10000. The device offers high precision as
a result of super-beta input transistors, which provide
exceptionally low input offset voltage, offset voltage
drift, input bias current, input voltage, and current
noise. Additional circuitry protects the inputs against
overvoltage up to ±60 V.
Low offset voltage: 10 µV (typ), 35 µV (max)
Gain drift: 5 ppm/°C (G = 1),
35 ppm/°C (G > 1) (max)
Noise: 8 nV/√Hz
Bandwidth: 2 MHz (G = 1), 270 kHz (G = 100)
Stable with 1-nF capacitive loads
Inputs protected up to ±60 V
Common-mode rejection: 110 dB, G = 10 (min)
Power-supply rejection: 100 dB, G = 1 (min)
Supply current: 385 µA (max)
Supply voltage range:
– Single supply: 4.5 V to 36 V
– Dual supply: ±2.25 V to ±18 V
Specified temperature: –40°C to +125°C
Package: 8-pin SOIC
1
•
•
•
•
•
•
•
•
•
•
The INA818 is optimized to provide a high commonmode rejection ratio. At G = 1, the common-mode
rejection ratio exceeds 90 dB across the full input
common-mode range. The device is designed for lowvoltage operation from a 4.5-V single supply, as well
as dual supplies up to ±18 V.
The INA818 is available in an 8-pin SOIC package
and is specified over the –40°C to +125°C
temperature range.
2 Applications
Device Information(1)
Industrial monitors
Flow transmitters
Battery test equipment
Multiparameter patient monitors
Analog input modules
Semiconductor test equipment
Portable instrumentation
PART NUMBER
INA818
INA818 Simplified Internal Schematic
-IN
RG
RG
+IN
40 k
22.5%
20%
25 k
±
25 k
+
17.5%
OUT
±
OverVoltage
Protection
50 k:
G 1
RG
4.90 mm × 3.91 mm
25%
40 k
+
±
RG
SOIC (8)
BODY SIZE (NOM)
Typical Distribution of Input Stage Offset Voltage
Drift
+VS
OverVoltage
Protection
PACKAGE
(1) For all available packages, see the package option addendum
at the end of the data sheet.
REF
+
40 k
40 k
Amplifiers (%)
•
•
•
•
•
•
•
15%
12.5%
10%
7.5%
5%
-VS
VO
G V
IN
V
IN
VREF
2.5%
0
-0.4
-0.3
-0.2
-0.1
0
0.1
0.2
0.3
Input Stage Offset Voltage Drift (PV/qC)
0.4
D002
1
An IMPORTANT NOTICE at the end of this data sheet addresses availability, warranty, changes, use in safety-critical applications,
intellectual property matters and other important disclaimers. PRODUCTION DATA.
INA818
SBOS894A – APRIL 2019 – REVISED JUNE 2019
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Table of Contents
1
2
3
4
5
6
7
Features ..................................................................
Applications ...........................................................
Description .............................................................
Revision History.....................................................
Device Comparison Table.....................................
Pin Configuration and Functions .........................
Specifications.........................................................
7.1
7.2
7.3
7.4
7.5
7.6
7.7
8
1
1
1
2
3
4
5
Absolute Maximum Ratings ...................................... 5
ESD Ratings ............................................................ 5
Recommended Operating Conditions....................... 5
Thermal Information .................................................. 5
Electrical Characteristics........................................... 6
Typical Characteristics: Table of Graphs .................. 8
Typical Characteristics ............................................ 10
Detailed Description ............................................ 19
8.1 Overview ................................................................. 19
8.2 Functional Block Diagram ....................................... 19
8.3 Feature Description................................................. 20
8.4 Device Functional Modes........................................ 26
9
Application and Implementation ........................ 26
9.1 Application Information............................................ 26
9.2 Typical Applications ................................................ 29
10 Power Supply Recommendations ..................... 32
11 Layout................................................................... 32
11.1 Layout Guidelines ................................................. 32
11.2 Layout Example .................................................... 33
12 Device and Documentation Support ................. 34
12.1
12.2
12.3
12.4
12.5
12.6
Documentation Support ........................................
Receiving Notification of Documentation Updates
Community Resources..........................................
Trademarks ...........................................................
Electrostatic Discharge Caution ............................
Glossary ................................................................
34
34
34
34
34
34
13 Mechanical, Packaging, and Orderable
Information ........................................................... 34
4 Revision History
NOTE: Page numbers for previous revisions may differ from page numbers in the current version.
Changes from Original (April 2019) to Revision A
•
2
Page
Changed document status from Advance Information to Production Data ........................................................................... 1
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SBOS894A – APRIL 2019 – REVISED JUNE 2019
5 Device Comparison Table
DEVICE
GAIN EQUATION
RG PINS AT PIN
INA818
35-µV Offset, 0.4 µV/°C VOS Drift, 8-nV/√Hz Noise, Low-Power,
Precision Instrumentation Amplifier
DESCRIPTION
G = 1 + 50 kΩ / RG
1, 8
INA819
35-µV Offset, 0.4 µV/°C VOS Drift, 8-nV/√Hz Noise, Low-Power,
Precision Instrumentation Amplifier
G = 1 + 50 kΩ / RG
2, 3
INA821
35-µV Offset, 0.4 µV/°C VOS Drift, 7-nV/√Hz Noise, HighBandwidth, Precision Instrumentation Amplifier
G = 1 + 49.4 kΩ / RG
2, 3
INA828
50-µV Offset, 0.5 µV/°C VOS Drift, 7-nV/√Hz Noise, Low-Power,
Precision Instrumentation Amplifier
G = 1 + 50 kΩ / RG
1, 8
INA333
25-µV VOS, 0.1 µV/°C VOS Drift, 1.8-V to 5-V, RRO, 50-µA IQ,
Chopper-Stabilized INA
G = 1 + 100 kΩ / RG
1, 8
PGA280
20-mV to ±10-V Programmable Gain IA With 3-V or 5-V
Differential Output; Analog Supply up to ±18 V
Digital programmable
N/A
INA159
G = 0.2 V Differential Amplifier for ±10-V to 3-V and 5-V
Conversion
G = 0.2 V/V
N/A
PGA112
Precision Programmable Gain Op Amp With SPI
Digital programmable
N/A
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6 Pin Configuration and Functions
D Package
8-Pin SOIC
Top View
RG
1
8
RG
±IN
2
7
+VS
+IN
3
6
OUT
±VS
4
5
REF
Not to scale
Pin Functions
PIN
NAME
NO.
I/O
DESCRIPTION
–IN
2
I
Negative (inverting) input
+IN
3
I
Positive (noninverting) input
OUT
6
O
Output
REF
5
I
Reference input. This pin must be driven by a low-impedance source.
RG
1, 8
—
Gain setting pin. Place a gain resistor between pin 1 and pin 8.
–VS
4
—
Negative supply
+VS
7
—
Positive supply
4
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SBOS894A – APRIL 2019 – REVISED JUNE 2019
7 Specifications
7.1 Absolute Maximum Ratings
over operating free-air temperature range (unless otherwise noted) (1)
MIN
MAX
UNIT
±20
V
40, (single
supply)
V
Supply voltage dual supply, VS = (V+) – (V–)
Supply voltage single supply, VS = (V+) – (V–)
Signal input pins
–60
60
V
VREF pin
–20
20
V
Signal output pins maximum voltage
(-Vs) - 0.5
(+Vs) + 0.5
Signal output pins maximum current
-50
50
Output short-circuit (2)
Continuous
Operating Temperature, TA
–50
150
Junction Temperature, TJ
175
Storage Temperature, Tstg
(1)
(2)
V
mA
–65
°C
150
Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. These are stress ratings
only, which do not imply functional operation of the device at these or any other conditions beyond those indicated under Recommended
Operating Conditions. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.
Short-circuit to VS / 2.
7.2 ESD Ratings
VALUE
V(ESD)
(1)
(2)
Electrostatic discharge
Human-body model (HBM), per ANSI/ESDA/JEDEC JS-001 (1)
±1500
Charged-device model (CDM), per JEDEC specification JESD22-C101 (2)
±750
UNIT
V
JEDEC document JEP155 states that 500-V HBM allows safe manufacturing with a standard ESD control process.
JEDEC document JEP157 states that 250-V CDM allows safe manufacturing with a standard ESD control process.
7.3 Recommended Operating Conditions
over operating free-air temperature range (unless otherwise noted)
Single-supply
Supply voltage VS
Dual-supply
Specified temperature
Specified temperature
MIN
MAX
4.5
36
±2.25
±18
–40
125
UNIT
V
°C
7.4 Thermal Information
INA818
THERMAL METRIC (1)
D (SOIC)
UNIT
8 PINS
RθJA
Junction-to-ambient thermal resistance
119.6
°C/W
RθJC(top)
Junction-to-case (top) thermal resistance
66.3
°C/W
RθJB
Junction-to-board thermal resistance
61.9
°C/W
ψJT
Junction-to-top characterization parameter
20.5
°C/W
ψJB
Junction-to-board characterization parameter
61.4
°C/W
RθJC(bot)
Junction-to-case (bottom) thermal resistance
N/A
°C/W
(1)
For more information about traditional and new thermal metrics, see the Semiconductor and IC Package Thermal Metrics application
report.
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SBOS894A – APRIL 2019 – REVISED JUNE 2019
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7.5 Electrical Characteristics
at TA = 25°C, VS = ±15 V, RL = 10 kΩ, VREF = 0 V, and G = 1 (unless otherwise noted)
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
10
35
UNIT
INPUT
Input stage offset
voltage (1) (2)
VOSI
75
µV
drift vs temperature, TA = –40°C to 125°C
0.4
µV/°C
300
µV
50
VOSO
Output stage offset
voltage (1) (2)
µV
TA = –40°C to 125°C (3)
TA = –40°C to 125°C (3)
800
drift vs temperature, TA = –40°C to 125°C
5
G = 1, RTI
110
120
G = 10, RTI
114
130
G = 100, RTI
130
135
G = 1000, RTI
136
µV
µV/°C
PSRR
Power-supply rejection
ratio
zid
Differential impedance
100 || 1
GΩ || pF
zic
Common-mode impedance
100 || 4
GΩ || pF
RFI filter, –3-dB frequency
Operating input range (4)
VCM
Input overvoltage range
CMRR
Common-mode rejection
ratio
dB
140
32
(V–) + 2
VS = ±2.25 V to ±18 V, TA = –40°C to 125°C
MHz
(V+) – 2
See Figure 51 to Figure 54
TA = –40°C to 125°C (3)
±60
At DC to 60 Hz, RTI, VCM = (V–) + 2 V to (V+) – 2 V,
G=1
90
105
At DC to 60 Hz, RTI, VCM = (V–) + 2 V to (V+) – 2 V,
G = 10
110
125
At DC to 60 Hz, RTI, VCM = (V–) + 2 V to (V+) – 2 V,
G = 100
130
145
At DC to 60 Hz, RTI, VCM = (V–) + 2 V to (V+) – 2 V,
G = 1000
140
150
V
V
dB
BIAS CURRENT
IB
Input bias current
IOS
Input offset current
VCM = VS / 2
0.15
TA = –40°C to 125°C
0.5
2
VCM = VS / 2
0.15
TA = –40°C to 125°C
0.5
2
nA
nA
NOISE VOLTAGE
eNI
Input stage voltage
noise (5)
f = 1 kHz, G = 100, RS = 0 Ω
eNO
Output stage voltage
noise (5)
f = 1 kHz, RS = 0 Ω
In
Noise current
8
fB = 0.1 Hz to 10 Hz, G = 100, RS = 0 Ω
nV/√Hz
0.19
µVPP
80
nV/√Hz
fB = 0.1 Hz to 10 Hz, RS = 0 Ω
2.6
µVPP
f = 1 kHz
130
fA/√Hz
fB = 0.1 Hz to 10 Hz, G = 100
4.7
pAPP
GAIN
Gain equation
G
GE
Gain error
Gain error drift (6)
(1)
(2)
(3)
(4)
(5)
(6)
6
1 + (50 kΩ / RG)
Gain
1
V/V
1000
G = 1, VO = ±10 V
±0.005%
±0.025%
G = 10, VO = ±10 V
±0.025%
±0.15%
G = 100, VO = ±10 V
±0.025%
±0.15%
G = 1000, VO = ±10 V
±0.05%
G = 1, TA = –40°C to 125°C, VO = ±10 V
±5
G > 1, TA = –40°C to 125°C, VO = ±10 V
±35
V/V
ppm/°C
Total offset, referred-to-input (RTI): VOS = (VOSI) + (VOSO / G).
Offset drifts are uncorrelated. Input-referred offset drift is calculated using: ΔVOS(RTI) = √[ΔVOSI2 + (ΔVOSO / G)2]
Specified by characterization.
Input voltage range of the INA818 input stage. The input range depends on the common-mode voltage, differential voltage, gain, and
reference voltage. See Typical Characteristic curves Figure 51 through Figure 54 for more information.
Total RTI voltage noise is equal to: eN(RTI) = √[eNI2 + (eNO / G)2]
The values specified for G > 1 do not include the effects of the external gain-setting resistor, RG.
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Electrical Characteristics (continued)
at TA = 25°C, VS = ±15 V, RL = 10 kΩ, VREF = 0 V, and G = 1 (unless otherwise noted)
PARAMETER
TEST CONDITIONS
MIN
G = 1 to 10, VO = –10 V to 10 V, RL = 10 kΩ
Gain nonlinearity
TYP
MAX
1
10
G = 100, VO = –10 V to 10 V, RL = 10 kΩ
UNIT
15
G = 1000, VO = –10 V to 10 V, RL = 10 kΩ
10
G = 1 to 100, VO = –10 V to 10 V, RL = 2 kΩ
30
ppm
OUTPUT
Voltage swing
(V–) + 0.15
Load capacitance stability
(V+) – 0.15
V
1000
pF
ZO
Closed-loop output
impedance
f = 10 kHz
5.0
Ω
ISC
Short-circuit current
Continuous to VS / 2
±20
mA
G=1
2.0
MHz
G = 10
890
G = 100
270
G = 1000
30
G = 1, VO = ±10 V
0.9
0.01%, G = 1 to 100, VSTEP = 10 V
12
0.01%, G = 1000, VSTEP = 10 V
40
0.001%, G = 1 to 100, VSTEP = 10 V
16
0.001%, G = 1000, VSTEP = 10 V
60
FREQUENCY RESPONSE
BW
SR
tS
Bandwidth, –3 dB
Slew rate
Settling time
kHz
V/µs
µs
REFERENCE INPUT
RIN
Input impedance
40
Voltage range
(V–)
Gain to output
kΩ
(V+)
1
Reference gain error
V
V/V
0.01%
POWER SUPPLY
IQ
Quiescent current
VIN = 0 V
350
VIN = 0 V, TA = –40°C to 125°C
385
520
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7.6 Typical Characteristics: Table of Graphs
Table 1. Table of Graphs
DESCRIPTION
FIGURE
Typical Distribution of Input Stage Offset Voltage
Figure 1
Typical Distribution of Input Stage Offset Voltage Drift
Figure 2
Typical Distribution of Output Stage Offset Voltage
Figure 3
Typical Distribution of Output Stage Offset Voltage Drift
Figure 4
Input Stage Offset Voltage vs Temperature
Figure 5
Output Stage Offset Voltage vs Temperature
Figure 6
Typical Distribution of Input Bias Current TA = 25°C
Figure 7
Typical Distribution of Input Bias Current TA = 90°C
Figure 8
Typical Distribution of Input Offset Current
Figure 9
Input Bias Current vs Temperature
Figure 10
Input Offset Current vs Temperature
Figure 11
Typical CMRR Distribution G = 1
Figure 12
Typical CMRR Distribution G = 10
Figure 13
CMRR vs Temperature G = 1
Figure 14
CMRR vs Temperature G = 10
Figure 15
Input Current vs Input Overvoltage
Figure 16
CMRR vs Frequency (RTI)
Figure 17
CMRR vs Frequency (RTI, 1-kΩ source imbalance)
Figure 18
Positive PSRR vs Frequency (RTI)
Figure 19
Negative PSRR vs Frequency (RTI)
Figure 20
Gain vs Frequency
Figure 21
Voltage Noise Spectral Density vs Frequency (RTI)
Figure 22
Current Noise Spectral Density vs Frequency (RTI)
Figure 23
0.1-Hz to 10-Hz RTI Voltage Noise G = 1
Figure 24
0.1-Hz to 10-Hz RTI Voltage Noise G = 1000
Figure 25
0.1-Hz to 10-Hz RTI Current Noise
Figure 26
Typical Distribution of Gain Error G = 1
Figure 28
Typical Distribution of Gain Error G = 10
Figure 29
Input Bias Current vs Common-Mode Voltage
Figure 27
Gain Error vs Temperature G = 1
Figure 30
Gain Error vs Temperature G = 10
Figure 31
.Supply Current vs Temperature
Figure 32
Gain Nonlinearity G = 1
Figure 33
Gain Nonlinearity G = 10
Figure 34
Offset Voltage vs Negative Common-Mode Voltage
Figure 35
Offset Voltage vs Positive Common-Mode Voltage
Figure 36
Positive Output Voltage Swing vs Output Current
Figure 37
Negative Output Voltage Swing vs Output Current
Figure 38
Short Circuit Current vs Temperature
Figure 39
Large-Signal Frequency Response
Figure 40
THD+N vs Frequency
Figure 41
Overshoot vs Capacitive Loads
Figure 42
Small-Signal Response G = 1
Figure 43
Small-Signal Response G = 10
Figure 44
Small-Signal Response G = 100
Figure 45
Small-Signal Response G = 1000
Figure 46
8
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Typical Characteristics: Table of Graphs (continued)
Table 1. Table of Graphs (continued)
DESCRIPTION
FIGURE
Large Signal Step Response
Figure 47
Closed-Loop Output Impedance
Figure 48
Differential-Mode EMI Rejection Ratio
Figure 49
Common-Mode EMI Rejection Ratio
Figure 50
Input Common-Mode Voltage vs Output Voltage G = 1, VS = 5 V
Figure 51
Input Common-Mode Voltage vs Output Voltage G = 100, VS = 5 V
Figure 52
Input Common-Mode Voltage vs Output Voltage VS =±5 V
Figure 53
Input Common-Mode Voltage vs Output Voltage VS =±15 V
Figure 54
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7.7 Typical Characteristics
at TA = 25°C, VS = ±15 V, RL = 10 kΩ, VREF = 0 V, and G = 1 (unless otherwise noted)
20%
25%
22.5%
20%
15%
Amplifiers (%)
Amplitude (%)
17.5%
10%
15%
12.5%
10%
7.5%
5%
5%
2.5%
0
-50
-40
-30
-20 -10
0
10
20
30
Input Stage Offset Voltage (PV)
N = 1555
Mean = 4.71 µV
40
0
-0.4
50
-0.3
D001
Std. Dev. = 7.12 µV
N = 45
-0.2
-0.1
0
0.1
0.2
0.3
Input Stage Offset Voltage Drift (PV/qC)
Mean = 0.0357 µV/°C
0.4
D002
Std. Dev. = 0.099 µV/°C
Figure 1. Typical Distribution of Input Stage Offset Voltage
Figure 2. Typical Distribution of Input Stage Offset Voltage
Drift
0.15
30%
0.1
20%
Amplifiers (%)
Amplifiers (%)
25%
0.05
15%
10%
5%
0
-200
-150
N = 1555
-100
-50
0
50
100
Output Stage Offset Voltage (PV)
Mean = –3.18 µV
150
Std. Dev. = 41.26 µV
N = 45
80
400
Output Stage Offset Voltage (PV)
500
60
40
20
0
-20
-40
Mean
+3V
-3V
-80
-100
-50
-25
0
25
50
75
Temperature (qC)
100
125
150
Mean = –1.49 µV/°C
4
5
D004
Std. Dev. = 0.89 µV/°C
Mean
+3V
-3V
300
200
100
0
-100
-200
-300
-400
-500
-50
D005
45 units, 1 wafer lot
-25
0
25
50
75
Temperature (qC)
100
125
150
D051
45 units, 1 wafer lots
Figure 5. Input Stage Offset Voltage vs Temperature
10
-3
-2
-1
0
1
2
3
Output Stage Offset Voltage Drift (PV/qC)
Figure 4. Typical Distribution of Output Stage Offset Voltage
Drift
100
-60
-4
D003
Figure 3. Typical Distribution of Output Stage Offset Voltage
Input Stage Offset Voltage (PV)
0
-5
200
Figure 6. Output Stage Offset Voltage vs Temperature
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Typical Characteristics (continued)
0.25
25%
0.2
20%
Amplifiers (%)
Amplifier (%)
at TA = 25°C, VS = ±15 V, RL = 10 kΩ, VREF = 0 V, and G = 1 (unless otherwise noted)
0.15
0.1
0.05
15%
10%
5%
0
-300
-200
N = 94
TA = 25°C
-100
0
100
Input Bias Current (pA)
Mean = 37.13 pA
200
0
-250 -200 -150 -100 -50
0
50 100
Input Bias Current (pA)
300
D006
Std. Dev. = 57.65 pA
N = 94
TA = 90°C
Figure 7. Typical Distribution of Input Bias Current
Mean = –27.65 pA
150
200
250
D007
Std. Dev. = 52.58 pA
Figure 8. Typical Distribution of Input Bias Current
25%
500
400
300
Input Bias Current (nA)
Amplifiers (%)
20%
15%
10%
5%
200
100
0
-100
-200
-300
Avg
3V
3V
-400
0
-300
-200
N = 94
-100
0
100
Input Offset Current (pA)
Mean = –38.82 pA
200
-500
-50
300
-25
D008
N = 94
Std. Dev. = 47.24 pA
Figure 9. Typical Distribution of Input Offset Current
0
25
50
75
Temperature (qC)
100
125
150
D009
G=1
Figure 10. Input Bias Current vs Temperature
300
20%
250
150
15%
100
Amplifiers (%)
Input Bias Current (nA)
200
50
0
-50
-100
-150
10%
5%
Avg
3V
3V
-200
-250
-300
-50
-30
N = 94
-10
10
30
50
70
90
Temperature (qC)
110
130
150
0
-20
D010
G=1
N = 94
G=1
Figure 11. Input Offset Current vs Temperature
-16
-12
-8
-4
0
4
8
12
Common-Mode Rejection Ratio (PV/V)
Mean = 3.23 µV/V
16
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Std. Dev. = 5.38 µV/V
Figure 12. Typical CMRR Distribution
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INA818
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Typical Characteristics (continued)
at TA = 25°C, VS = ±15 V, RL = 10 kΩ, VREF = 0 V, and G = 1 (unless otherwise noted)
150
Common-Mode Rejection Ratio (dB)
25%
15%
10%
5%
0
-2
-1.5
N = 94
G = 10
-1
-0.5
0
0.5
1
Common-Mode Rejection Ratio (PV/V)
Mean = 0.34 µV/V
125
100
Unit 1
Unit 2
Unit 3
Unit 4
Unit 5
75
50
-50
1.5
-25
Std. Dev. = 0.54 µV/V
Figure 13. Typical CMRR Distribution
Input Current (mA)
Common-Mode Rejection Ratio (dB)
125
100
Unit 1
Unit 2
Unit 3
Unit 4
Unit 5
-25
0
25
50
75
Temperature (qC)
5 typical units
100
125
150
D013
G=1
125
150
10
20
8
16
6
12
4
8
2
4
0
0
-2
-4
-4
-8
-6
-12
-8
Input Current
-16
Output Voltage
-20
20
30
40
50
-10
-50
-40
-30
D014
-20
-10
0
10
Input Voltage (V)
D015
VS = 36 V
G = 10
Figure 15. CMRR vs Temperature
Figure 16. Input Current vs Input Overvoltage
160
150
1
10
100
1000
140
120
1
10
100
1000
125
100
100
CMRR (dB)
CMRR (dB)
100
Figure 14. CMRR vs Temperature
150
50
-50
25
50
75
Temperature (qC)
5 typical units
175
75
0
D012
Output Voltage (V)
Amplifiers (%)
20%
80
60
75
50
40
25
20
0
0
1
10
100
1k
10k
Frequency (Hz)
100k
1M
1
D016
10
100
1k
10k
Frequency (Hz)
100k
1M
D017
1-kΩ source imbalance
Figure 17. CMRR vs Frequency (RTI)
12
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Figure 18. CMRR vs Frequency (RTI)
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Typical Characteristics (continued)
at TA = 25°C, VS = ±15 V, RL = 10 kΩ, VREF = 0 V, and G = 1 (unless otherwise noted)
170
160
140
140
Negative Power Supply
Rejection Ratio (dB)
Positive Power Supply
Rejection Ratio (dB)
120
110
80
50
20
G=1
G = 10
G = 100
G = 1000
-10
100
80
60
40
20
G=1
G = 10
G = 100
G = 1000
0
-20
-40
-40
1
10
100
1k
10k
Frequency (Hz)
100k
1M
1
60
500
300
200
40
20
0
-20
-60
10
G=1
G = 10
G = 100
G = 1000
100
1k
10k
100k
Frequency (Hz)
1M
10k
100k
D019
G=1
G = 100
100
50
30
20
10
5
3
2
1
100m
10M
1
10
D020
Figure 21. Gain vs Frequency
100
1k
Frequency (Hz)
10k
100k
D021
Figure 22. Voltage Noise Spectral Density vs Frequency
(RTI)
3
1000
700
500
2
300
200
Noise (PV/div)
Current Noise
Spectral Density (fA/—Hz)
100
1k
Frequency (Hz)
Figure 20. Negative PSRR vs Frequency (RTI)
1000
Voltage Noise
Spectral Density (nV/—Hz)
Closed Loop Gain (dB)
Figure 19. Positive PSRR vs Frequency (RTI)
80
-40
10
D018
100
70
50
1
0
-1
30
-2
20
10
100m
-3
1
10
100
Frequency (Hz)
1k
10k
0
1
D022
2
3
4
5
6
Time (s/div)
7
8
9
10
D023
G=1
Figure 23. Current Noise Spectral Density vs Frequency
(RTI)
Figure 24. 0.1-Hz to 10-Hz RTI Voltage Noise
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Typical Characteristics (continued)
at TA = 25°C, VS = ±15 V, RL = 10 kΩ, VREF = 0 V, and G = 1 (unless otherwise noted)
100
2
80
1.5
1
40
Noise (1 pA/div)
Noise (20 nV/div)
60
20
0
-20
-40
0.5
0
-0.5
-1
-60
-1.5
-80
-100
-5
-4
-3
-2
-1
0
1
Time (1 s/div)
2
3
4
-2
-5
5
-4
-3
-2
D024
-1
0
1
Time (1 s/div)
2
3
4
5
D025
G = 1000
Figure 25. 0.1-Hz to 10-Hz RTI Voltage Noise
Figure 26. 0.1-Hz to 10-Hz RTI Current Noise
0.5
20%
0.4
17.5%
15%
0.2
Amplifiers (%)
Input Bias Current (nA)
0.3
0.1
0
-0.1
12.5%
-0.2
10%
7.5%
5%
-0.3
45 qC
25 qC
125 qC
-0.4
-0.5
-15
-12
-9
-6
-3
0
3
6
Common Mode Voltage (V)
9
12
2.5%
0
-250 -200 -150 -100 -50
0
50 100
Gain Error (ppm)
15
D026
VS = ±15 V
N = 94
G=1
Figure 27. Input Bias Current vs Common-Mode Voltage
Mean = –48 ppm
150
200
250
D027
Std. Dev. = 58 ppm
Figure 28. Typical Distribution of Gain Error G = 1
-20
20%
18%
-30
16%
Gain Error (ppm)
Amplifiers (%)
14%
12%
10%
8%
6%
4%
-40
-50
-60
-70
2%
0
-300
N = 94
G = 10
-150
0
150
300
450
Gain Error (ppm)
Mean = 286 ppm
600
750
900
-80
-50
D028
Std. Dev. = 204 ppm
Figure 29. Typical Distribution of Gain Error G = 10
14
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-25
0
25
50
75
Temperature (qC)
100
125
150
D029
G=1
Figure 30. Gain Error vs Temperature
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Typical Characteristics (continued)
at TA = 25°C, VS = ±15 V, RL = 10 kΩ, VREF = 0 V, and G = 1 (unless otherwise noted)
0.5
500
450
0.45
350
300
IQ (mA)
Gain Error (ppm)
400
250
200
0.4
0.35
150
100
0.3
VS = r 15 V
VS = r 2.25 V
50
0
-50
-25
0
25
50
75
Temperature (qC)
100
125
0.25
-60
150
-30
0
D030
30
60
Temperature (qC)
90
120
150
D031
G = 10
Figure 31. Gain Error vs Temperature
Figure 32. Supply Current vs Temperature
5
1
EP
LREG
0.6
3
0.4
2
0.2
0
-0.2
-0.4
1
0
-1
-2
-0.6
-3
-0.8
-4
-1
-10
-8
-6
-4
-2
0
2
Output Voltage (V)
4
6
8
EP
LREG
4
Nonlinearity (ppm)
Nonlinearity (ppm)
0.8
-5
-10
10
-8
-6
D032
G=1
-2
0
2
Output Voltage (V)
4
6
8
10
D033
G = 10
Figure 33. Gain Nonlinearity
Figure 34. Gain Nonlinearity
150
175
40 qC
25 qC
85 qC
125 qC
150
40 qC
25 qC
85 qC
125 qC
125
100
Offset Voltage (PV)
125
Offset Voltage (PV)
-4
100
75
50
25
0
75
50
25
0
-25
-25
-50
-75
-15
-14.6
-14.2 -13.8 -13.4
-13
-12.6
Input Common-Mode Voltage (V)
-12.2
-11.8
-50
12
D034
Figure 35. Offset Voltage vs Negative Common-Mode
Voltage
12.4
12.8
13.2
13.6
14
Input Common-Mode Voltage (V)
14.4
14.8
D035
Figure 36. Offset Voltage vs Positive Common-Mode
Voltage
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Typical Characteristics (continued)
at TA = 25°C, VS = ±15 V, RL = 10 kΩ, VREF = 0 V, and G = 1 (unless otherwise noted)
15
-14
-40qC
25qC
85qC
125qC
14.9
14.8
-14.2
-14.3
Output Voltage (V)
Output Voltage (V)
14.7
14.6
14.5
14.4
14.3
-14.4
-14.5
-14.6
-14.7
14.2
-14.8
14.1
-14.9
14
-15
0
4
8
Output Current (mA)
12
16
0
12
14
16
D037
VS = r15 V
VS = r5 V
18
16
Output Amplitude (Vp)
20
10
0
-10
-20
-30
14
12
10
8
6
-40
4
-50
2
-30
-10
10
30
50
70
90
Temperature (qC)
110
130
0
100
150
-80
100
1k
Frequency (Hz)
10k
-100
100k
10M
D039
45
40
35
Overshoot (%)
-60
1M
50
Total Harmonic Distortion + Noise (dB)
G=1
G = 10
G = 100
0.01
10k
100k
Frequency (Hz)
Figure 40. Large-Signal Frequency Response
-40
0.1
1k
D038
Figure 39. Short Circuit Current vs Temperature
1
Total Harmonic Distortion + Noise (%)
6
8
10
Output Current (mA)
20
ISC, Source
ISC, Sink
30
0.001
10
4
Figure 38. Negative Output Voltage Swing vs Output Current
40
-60
-50
2
D036
Figure 37. Positive Output Voltage Swing vs Output Current
Short Circuit Current (mA)
-40qC
25qC
85qC
125qC
-14.1
30
25
20
15
10
Positive
Negative
5
0
1
D040
10
100
Cload (pF)
1k
D041
500-kHz measurement bandwidth
1-VRMS output voltage
100-kΩ load
Figure 41. THD+N vs Frequency
16
Figure 42. Overshoot vs Capacitive Loads
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Typical Characteristics (continued)
100
100
80
80
60
60
Output Amplitude (mV)
Output Amplitude (mV)
at TA = 25°C, VS = ±15 V, RL = 10 kΩ, VREF = 0 V, and G = 1 (unless otherwise noted)
40
20
0
-20
-40
-60
40
20
0
-20
-40
-60
-80
-80
-100
-5
-100
-5
-2.5
0
G=1
2.5
5
7.5
Time (Ps)
10
12.5
15
-2.5
RL = 10 kΩ
CL = 100 pF
5
7.5
Time (Ps)
10
12.5
15
D043
RL = 10 kΩ
Figure 43. Small-Signal Response
CL = 100 pF
Figure 44. Small-Signal Response
100
80
80
60
60
Output Amplitude (mV)
Output Amplitude (mV)
2.5
G = 10
100
40
20
0
-20
-40
-60
40
20
0
-20
-40
-60
-80
-100
-5
0
D042
-80
-2.5
0
G = 100
2.5
5
7.5
Time (Ps)
RL = 10 kΩ
10
12.5
-100
-25 -12.5
15
0
12.5
D044
CL = 100 pF
G = 1000
Figure 45. Small-Signal Response
25
37.5 50
Time (Ps)
62.5
75
87.5 100
D045
RL = 10 kΩ
CL = 100 pF
Figure 46. Small-Signal Response
Output
Input
Amplitude (2 V/div)
Output Impedance (:)
1k
100
10
1
0.1
Time (10 µs/div)
1
10
100
1k
10k
Frequency (Hz)
100k
1M
10M
C0xx
Figure 47. Large Signal Step Response
Figure 48. Closed-Loop Output Impedance
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Typical Characteristics (continued)
at TA = 25°C, VS = ±15 V, RL = 10 kΩ, VREF = 0 V, and G = 1 (unless otherwise noted)
100
140
120
EMIRR (dB)
EMIRR (dB)
80
60
40
100
80
60
20
40
0
10M
100M
1G
Frequency (Hz)
20
10M
10G
Figure 49. Differential-Mode EMI Rejection Ratio
VREF = 0 V
VREF = 2.5 V
4
3
2
1
0
1
2
3
4
5
Output Voltage (V)
VS = 5 V
VREF = 0 V
VREF = 2.5 V
4
3
2
1
0
6
1
2
G=1
3
4
5
6
Output Voltage (V)
C006
VS = 5 V
Figure 51. Input Common-Mode Voltage vs Output Voltage
C006
G = 100
Figure 52. Input Common-Mode Voltage vs Output Voltage
15
5
Common-Mode Voltage (V)
4
Common-Mode Voltage (V)
D048
0
0
3
2
1
0
-1
-2
-3
G=1
-4
G = 100
-5
±6
±4
VS = ±5 V
10
5
0
-5
-10
-15
G=1
G = 100
-20
±2
0
Output Voltage (V)
2
4
6
±20
VREF = 0 V
±10
0
Output Voltage (V)
C006
VS = ±15 V
Figure 53. Input Common-Mode Voltage vs Output Voltage
18
10G
Figure 50. Common-Mode EMI Rejection Ratio
5
Common-Mode Voltage (V)
Common-Mode Voltage (V)
5
100M
1G
Frequency (Hz)
D047
10
20
C006
VREF = 0 V
Figure 54. Input Common-Mode Voltage vs Output Voltage
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8 Detailed Description
8.1 Overview
The INA818 is a monolithic, precision instrumentation amplifier incorporating a current-feedback input stage and
a four-resistor difference amplifier output stage. The functional block diagram in the next section shows how the
differential input voltage is buffered by transistors Q1 and Q2 and is forced across resistor RG, which causes a
signal current to flow through resistors RG, R1, and R2. The output difference amplifier, A3, removes the commonmode component of the input signal and refers the output signal to the REF pin. The VBE and voltage drop
across R1 and R2 produce output voltages on A1 and A2 that are approximately 0.8 V lower than the input
voltages.
Each input is protected by two field-effect transistors (FETs) that provide a low series resistance under normal
signal conditions, and preserve excellent noise performance. When excessive voltage is applied, these
transistors limit input current to approximately 8 mA.
8.2 Functional Block Diagram
+VS
VB
RB
IB Cancellation
RB
IB Cancellation
-VS +VS
40 k
±
±
+
±
+
40 k
A1
A2
A3
OUT
+
40 k
REF
40 k
+VS
+VS
-VS +VS
Q1
-IN
Overvoltage
Protection
SuperNPN
+VS
R1
25 k
+VS
RG
-VS
Q2
+IN
Overvoltage
Protection
R2
25 k
RG
(External)
-VS
SuperNPN
-VS
RG
-VS
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8.3 Feature Description
8.3.1 Setting the Gain
Figure 55 shows that the gain of the INA818 is set by a single external resistor (RG) connected between the RG
pins (pins 1 and 8).
V+
+VS
Overvoltage
Protection
-IN
1
50 k:
RG
40 k
±
RG
G
40 k
+
RG
25 k
±
25 k
+
OUT
VO
RG
G V
IN
V
IN
VREF
±
Overvoltage
Protection
+IN
+
40 k
40 k
REF
-VS
Copyright © 2017, Texas Instruments Incorporated
V-
Figure 55. Simplified Diagram of the INA818 With Gain and Output Equations
The value of RG is selected according to Equation 1:
50 k:
G 1
RG
(1)
Table 2 lists several commonly-used gains and resistor values. The 50-kΩ term in Equation 1 comes from the
sum of the two internal 25-kΩ feedback resistors. These on-chip resistors are laser-trimmed to accurate absolute
values. The accuracy and temperature coefficients of these resistors are included in the gain accuracy and drift
specifications of the INA818. As shown in Figure 55 and explained in more details in the Layout section, make
sure to connect low-ESR, 0.1-µF ceramic bypass capacitors between each supply pin and ground that are placed
as close to the device as possible.
Table 2. Commonly-Used Gains and Resistor Values
20
DESIRED GAIN
RG (Ω)
NEAREST 1% RG (Ω)
1
NC
NC
2
50 k
49.9 k
5
12.5 k
12.4 k
10
5.556 k
5.49 k
20
2.632 k
2.61 k
50
1.02 k
1.02 k
100
505.1
511
200
251.3
249
500
100.2
100
1000
50.05
49.9
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8.3.1.1 Gain Drift
The stability and temperature drift of the external gain setting resistor (RG ) also affects gain. The contribution of
RG to gain accuracy and drift is determined from Equation 1.
The best gain drift of 5 ppm/℃ (maximum) is achieved when the INA818 uses G = 1 without RG connected. In
this case, gain drift is limited by the mismatch of the temperature coefficient of the integrated 40-kΩ resistors in
the differential amplifier (A3). At gains greater than 1, gain drift increases as a result of the individual drift of the
25-kΩ resistors in the feedback of A1 and A2, relative to the drift of the external gain resistor (RG.) The low
temperature coefficient of the internal feedback resistors improves the overall temperature stability of applications
using gains greater than 1 V/V over alternate solutions.
Low resistor values required for high gain make wiring resistance an important consideration. Sockets add to the
wiring resistance and contribute additional gain error (such as a possible unstable gain error) at gains of
approximately 100 or greater. To maintain stability, avoid parasitic capacitance of more than a few picofarads at
RG connections. Careful matching of any parasitics on the RG pins maintains optimal CMRR over frequency.
8.3.2 EMI Rejection
Texas Instruments developed a method to accurately measure the immunity of an amplifier over a broad
frequency spectrum extending from 10 MHz to 6 GHz. This method uses an EMI rejection ratio (EMIRR) to
quantify the ability of the INA818 to reject EMI. The offset resulting from an input EMI signal is calculated using
Equation 2:
'VOS
§ VRF _ PEAK 2
¨
¨ 100 mVP
©
·
¸ ˜ 10
¸
¹
§ EMIRR (dB) ·
¨
¸
20
©
¹
where
•
VRF_PEAK is the peak amplitude of the input EMI signal.
(2)
Figure 56 and Figure 57 show the INA818 EMIRR graphs for differential and common-mode EMI rejection across
this frequency range. Table 3 lists the EMIRR values for the INA818 at frequencies commonly encountered in
real-world applications. Applications listed in Table 3 are centered on or operated near the frequency shown.
Depending on the end-system requirements, additional EMI filters may be required near the signal inputs of the
system. Incorporating known good practices, such as using short traces, low-pass filters, and damping resistors
combined with parallel and shielded signal routing may also be required.
140
100
80
100
EMIRR (dB)
EMIRR (dB)
120
80
60
40
60
20
40
20
10M
100M
1G
Frequency (Hz)
10G
0
10M
D048
Figure 56. Common-Mode EMIRR Testing
100M
1G
Frequency (Hz)
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Figure 57. Differential Mode EMIRR Testing
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Table 3. INA818 EMIRR for Frequencies of Interest
FREQUENCY
APPLICATION OR ALLOCATION
DIFFERENTIAL
EMIRR
COMMON-MODE
EMIRR
400 MHz
Mobile radio, mobile satellite, space operation, weather, radar, ultrahigh-frequency (UHF)
applications
52 dB
80 dB
900 MHz
Global system for mobile communications (GSM) applications, radio communication, navigation,
GPS (up to 1.6 GHz), GSM, aeronautical mobile, UHF applications
55 dB
71 dB
1.8 GHz
GSM applications, mobile personal communications, broadband, satellite,
L-band (1 GHz to 2 GHz)
58 dB
73 dB
®
2.4 GHz
802.11b, 802.11g, 802.11n, Bluetooth , mobile personal communications, industrial, scientific
and medical (ISM) radio band, amateur radio and satellite, S-band (2 GHz to 4 GHz)
59 dB
95 dB
3.6 GHz
Radiolocation, aero communication and navigation, satellite, mobile, S-band
78 dB
96 dB
802.11a, 802.11n, aero communication and navigation, mobile communication, space and
satellite operation, C-band (4 GHz to 8 GHz)
70 dB
100 dB
5 GHz
8.3.3 Input Common-Mode Range
The linear input voltage range of the INA818 input circuitry extends within 1.5 V (typical) of both power supplies
and maintains excellent common-mode rejection throughout this range. The common-mode range for the most
common operating conditions are shown in Figure 58, Figure 53, and Figure 54. The common-mode range for
other operating conditions is best calculated using the Common-Mode Input Range Calculator for Instrumentation
Amplifiers.
5
VREF = 0 V
VREF = 2.5 V
Common-Mode Voltage (V)
Common-Mode Voltage (V)
5
4
3
2
1
0
1
2
3
4
5
Output Voltage (V)
VS = 5 V
3
2
1
0
6
1
2
3
4
5
6
Output Voltage (V)
C006
G=1
VS = 5 V
Figure 58. Input Common-Mode Voltage vs Output Voltage
C006
G = 100
Figure 59. Input Common-Mode Voltage vs Output Voltage
15
5
Common-Mode Voltage (V)
4
Common-Mode Voltage (V)
VREF = 2.5 V
4
0
0
3
2
1
0
-1
-2
-3
G=1
-4
G = 100
-5
±6
±4
VS = ±5 V
10
5
0
-5
-10
-15
G=1
G = 100
-20
±2
0
Output Voltage (V)
2
4
6
±20
VREF = 0 V
±10
0
Output Voltage (V)
C006
VS = ±15 V
Figure 60. Input Common-Mode Voltage vs Output Voltage
22
VREF = 0 V
10
20
C006
VREF = 0 V
Figure 61. Input Common-Mode Voltage vs Output Voltage
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8.3.4 Input Protection
The inputs of the INA818 device are individually protected for voltages up to ±60 V. For example, a condition of
–60 V on one input and +60 V on the other input does not cause damage. Internal circuitry on each input
provides low series impedance under normal signal conditions. If the input is overloaded, the protection circuitry
limits the input current to a value of approximately 8 mA.
+V
ZD1
+VS
Input Voltage
Source
IN
+
Overvoltage
Protection
Input Transistor
±
-VS
ZD2
-V
Figure 62. Input Current Path During an Overvoltage Condition
10
20
8
16
6
12
4
8
2
4
0
0
-2
-4
-4
-8
-6
-12
-8
Input Current
-16
Output Voltage
-20
20
30
40
50
-10
-50
-40
-30
-20
-10
0
10
Input Voltage (V)
Output Voltage (V)
Input Current (mA)
During an input overvoltage condition, current flows through the input protection diodes into the power supplies;
see Figure 62. If the power supplies are unable to sink current, then Zener diode clamps (ZD1 and ZD2 in
Figure 62) must be placed on the power supplies to provide a current pathway to ground. Figure 63 shows the
input current for input voltages from –50 V to +50 V when the INA818 is powered by ±15-V supplies.
D015
Figure 63. Input Current vs Input Overvoltage
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8.3.5 Operating Voltage
The INA818 operates over a power-supply range of 4.5 V to 36 V (±2.25 V to ±18 V).
CAUTION
Supply voltages higher than 40 V (±20 V) can permanently damage the device.
Parameters that vary over supply voltage or temperature are shown in Typical
Characteristics .
8.3.6 Error Sources
Most modern signal-conditioning systems calibrate errors at room temperature. However, calibration of errors
that result from a change in temperature is normally difficult and costly. Therefore, minimize these errors by
choosing high-precision components, such as the INA818, that have improved specifications in critical areas that
impact the precision of the overall system. Figure 64 shows an example application.
+15 V
RG
5.49 k
INA
RG
VCM
10 V
RS±
0.99 k
VOUT
1V
±VS
VDIFF = VOUT / G
REF
RS+
1k
+VS
C2
C1
±15 V
Figure 64. Example Application With G = 10 V/V and 1-V Output Voltage
Resistor-adjustable devices (such as the INA818) show the lowest gain error in G = 1 because of the inherently
well-matched drift of the internal resistors of the differential amplifier. At gains greater than 1 (for instance, G =
10 V/V or G = 100 V/V), the gain error becomes a significant error source because of the contribution of the
resistor drift of the 25-kΩ feedback resistors in conjunction with the external gain resistor. Except for very high
gain applications, the gain drift is by far the largest error contributor compared to other drift errors, such as offset
drift.
The INA818 offers excellent gain error over temperature for both G > 1 and G = 1 (no external gain resistor).
Table 5 summarizes the major error sources in common INA applications and compares the three cases of G = 1
(no external resistor) and G = 10 (5.49-kΩ external resistor) and G = 100 (511-Ω external resistor). All
calculations are assuming an output voltage of VOUT = 1 V. Thus, the input signal VDIFF (given by VDIFF= VOUT /
G) exhibits smaller and smaller amplitudes with increasing gain G. VDIFF = 1 mV at G = 1000 in this example. All
calculations refer the error to the input for easy comparison and system evaluation. As Table 5 shows, errors
generated by the input stage (such as input offset voltage) are more dominant at higher gain, while the effects of
output stage are suppressed because they are divided by the gain when referring them back to the input. The
gain error and gain drift error are much more significant for gains greater than 1 because of the contribution of
the resistor drift of the 25-kΩ feedback resistors in conjunction with the external gain resistor. In most
applications, static errors (absolute accuracy errors) can readily be removed during calibration in production,
while the drift errors are the key factors limiting overall system performance.
24
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Table 4. System Specifications for Error Calculation
QUANTITY
VALUE
UNIT
VOUT
1
V
VCM
10
V
VS
1
V
RS+
1000
Ω
RS–
999
Ω
RG tolerance
0.01
%
RG drift
10
ppm/°C
Temperature range upper limit
105
°C
Table 5. Error Calculation
INA818 VALUES
ERROR SOURCE
ERROR CALCULATION
SPECIFICATION
UNIT
G=1
ERROR
(ppm)
G = 100
ERROR
(ppm)
G = 1000
ERROR
(ppm)
ABSOLUTE ACCURACY AT 25°C
Input offset voltage
VOSI / VDIFF
35
µV
35
350
3500
Output offset voltage
VOSO / (G × VDIFF)
300
µV
300
300
300
Input offset current
IOS × maximum (RS+, RS–) / VDIFF
0.5
nA
1
5
50
dB
316
316
316
CMRR (min)
VCM / (10CMRR/20 × VDIFF)
90 (G = 1),
110 (G = 10),
130 (G = 100)
PSRR (min)
(VCC -VS)/ (10PSRR/20 × VDIFF)
110 (G = 1),
114 (G = 10),
130 (G = 100)
dB
3
20
32
Gain error from INA (max)
GE(%) × 104
0.02 (G = 1),
0.15 (G = 10, 100)
%
200
1500
1500
Gain error from external resistor RG (max)
GE(%) × 104
0.01
%
100
100
100
Total absolute accuracy error (ppm) at 25°C,
worst case
sum of all errors
—
—
955
2591
5798
Total absolute accuracy error (ppm) at 25°C,
average
rms sum of all errors
—
—
491
1604
3835
5 (G = 1),
35 (G = 10, 100)
ppm/°C
400
2800
2800
DRIFT TO 105°C
Gain drift from INA (max)
GTC × (TA – 25)
Gain drift from external resistor RG (max)
GTC × (TA – 25)
10
ppm/°C
800
800
800
Input offset voltage drift (max)
(VOSI_TC / VDIFF) × (TA – 25)
0.4
µV/°C
32
320
3200
Output offset voltage drift
[VOSO_TC / ( G × VDIFF)] × (TA – 25)
5
µV/°C
400
400
400
Offset current drift
IOS_TC × maximum (RS+, RS–) ×
(TA – 25) / VDIFF
20
pA/°C
2
16
160
Total drift error to 105°C (ppm), worst case
sum of all errors
—
—
1634
4336
7360
Total drift error to 105°C (ppm), typical
rms sum of all errors
—
—
980
2957
4348
10 (G = 1, 10),
15 (G = 100)
ppm of FS
10
10
15
eNI = 8,
eNO = 90
µVPP
1204
1070
3941
0.13
pA/√Hz
0.3
2
11
RESOLUTION
Gain nonlinearity
Voltage noise (at 1 kHz)
BW ´
(eNI2 +
eNO
G
2
6
´
VDIFF
Current noise (at 1kHz)
IN × maximum (RS+, RS–) × √BW /
VDIFF
Total resolution error (ppm), worst case
sum of all errors
—
—
1214
1080
3956
Total resolution error (ppm), typical
rms sum of all errors
—
—
1204
1070
3941
Total error (ppm), worst case
sum of all errors
—
—
3802
8007
17113
Total error (ppm), typical
rms sum of all errors
—
—
1628
3530
7010
TOTAL ERROR
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8.4 Device Functional Modes
The INA818 has a single functional mode and operates when the power-supply voltage is greater than 4.5 V
(±2.25 V). The maximum power-supply voltage for the INA818 is 36 V (±18 V.)
9 Application and Implementation
NOTE
Information in the following applications sections is not part of the TI component
specification, and TI does not warrant its accuracy or completeness. TI’s customers are
responsible for determining suitability of components for their purposes. Customers should
validate and test their design implementation to confirm system functionality.
9.1 Application Information
9.1.1 Reference Pin
The output voltage of the INA818 is developed with respect to the voltage on the reference pin, REF. In dualsupply operation, REF (pin 6) is connected to the low-impedance system ground. In single-supply operation,
offsetting the output signal to a precise midsupply level is useful (for example, 2.5 V in a 5-V supply
environment). To accomplish this level shift, a voltage source must be connected to the REF pin to level-shift the
output so that the INA818 drives a single-supply ADC.
The voltage source applied to the reference pin must have a low output impedance. As shown in Figure 65, any
resistance at the reference pin (shown as RREF in Figure 65) is in series with an internal 40-kΩ resistor.
V+
+VS
-IN
Overvoltage
Protection
40 k
±
RG
RG
RG
+IN
40 k
+
25 k
±
25 k
+
OUT
±
Overvoltage
Protection
REF
+
40 k
40 k
RREF
-VS
V-
Figure 65. Parasitic Resistance Shown at the Reference Pin
26
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Application Information (continued)
The parasitic resistance at the reference pin (RREF) creates an imbalance in the four resistors of the internal
difference amplifier, which degrades the common-mode rejection ratio (CMRR). Figure 66 shows the degradation
in CMRR of the INA818 as a result of increased resistance at the reference pin. For the best performance, keep
the source impedance to the REF pin (RREF) below 5 Ω.
Common-Mode Rejection Ratio (dB)
120
100
80
60
0Ω
5Ω
40
10 Ω
20
15 Ω
20 Ω
0
10
100
1k
10k
Frequency (Hz)
Figure 66. The Effect of Increasing Resistance at the Reference Pin
Voltage-reference devices are a suitable option for providing a low-impedance voltage source for the reference
pin. However, if a resistor voltage divider generates a reference voltage, the divider must be buffered by an op
amp, as Figure 67 shows, in order to avoid CMRR degradation.
±IN
OUT
±VS
INA818
RG
REF
RG
RG
5V
OPA191
5V
100 k
+
+IN
+VS
5V
1 F
100 k
±
Figure 67. Using an Op Amp to Buffer Reference Voltages
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Application Information (continued)
9.1.2 Input Bias Current Return Path
The input impedance of the INA818 is extremely high—approximately 100 GΩ. However, a path must be
provided for the input bias current of both inputs. This input bias current is typically 150 pA. High input
impedance means that this input bias current changes very little with varying input voltage.
For proper operation, input circuitry must provide a path for input bias current. Figure 68 shows various
provisions for an input bias current path. Without a bias current path, the inputs float to a potential that exceeds
the common-mode range of the INA818, and the input amplifiers saturate. If the differential source resistance is
low, the bias current return path can connect to one input (as shown in the thermocouple example in Figure 68).
With a higher source impedance, using two equal resistors provides a balanced input with possible advantages
of a lower input offset voltage as a result of bias current and better high-frequency common-mode rejection.
Microphone,
Hydrophone,
and So Forth
TI Device
47 kW
47 kW
Thermocouple
TI Device
10 kW
TI Device
Center tap provides
bias current return.
Copyright © 2017, Texas Instruments Incorporated
Figure 68. Providing an Input Common-Mode Current Path
28
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9.2 Typical Applications
9.2.1 Three-Pin Programmable Logic Controller (PLC)
Figure 69 shows a three-pin programmable-logic controller (PLC) design for the INA818. This PLC reference
design accepts inputs of ±10 V or ±20 mA. The output is a single-ended voltage of 2.5 V ±2.3 V (or 200 mV to
4.8 V). Many PLCs typically have these input and output ranges.
±10 V
REF5025
R1 = 100 NŸ
1 F
VIN
GND
NR
1 F 1 F
15 V
R2 = 4.17 NŸ
±20 mA
VOUT
15 V
-IN +VS
RG
REF
R3 =
INA818
RG = 10.5 NŸ
20 Ÿ
RG
+IN
VOUT 2.5 V ± 2.3 V
OUT
-VS
-15 V
Copyright © 2017, Texas Instruments Incorporated
Figure 69. PLC Input (±10 V, 4 mA to 20 mA)
9.2.1.1 Design Requirements
For this application, the design requirements are as follows:
• 4-mA to 20-mA input with less than 20-Ω burden
• ±20-mA input with less than 20-Ω burden
• ±10-V input with impedance of approximately 100 kΩ
• Maximum 4-mA to 20-mA or ±20-mA burden voltage equal to ±0.4 V
• Output range within 0 V to 5 V
9.2.1.2 Detailed Design Procedure
There are two modes of operation for the circuit shown in Figure 69: current input and voltage input. This design
requires R1 >> R2 >> R3. Given this relationship, Equation 3 calculates the current input mode transfer function.
VOUT-I = VD ´ G + VREF = -(IIN ´ R3) ´ G + VREF
where
•
•
•
•
G represents the gain of the instrumentation amplifier
VD represents the differential voltage at the INA818 inputs
VREF is the voltage at the INA818 REF pin
IIN is the input current
(3)
Equation 4 shows the transfer function for the voltage input mode.
R2
VOUT-V = VD ´ G + VREF = - VIN ´
´ G + VREF
R 1 + R2
where
•
VIN is the input voltage
(4)
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Typical Applications (continued)
R1 sets the input impedance of the voltage input mode. The minimum typical input impedance is 100 kΩ. 100 kΩ
is selected for R1 because increasing the R1 value also increases noise. The value of R3 must be extremely
small compared to R1 and R2. 20 Ω for R3 is selected because that resistance value is much smaller than R1 and
yields an input voltage of ±400 mV when operated in current mode (±20 mA).
Use Equation 5 to calculate R2 given VD = ±400 mV, VIN = ±10 V, and R1 = 100 kΩ.
R2
R ´ VD
VD = VIN ´
® R2 = 1
= 4.167 kW
R 1 + R2
VIN - VD
(5)
The value obtained from Equation 5 is not a standard 0.1% value, so 4.17 kΩ is selected. R1 and R2 also use
0.1% tolerance resistors to minimize error.
Use Equation 6 to calculate the ideal gain of the instrumentation amplifier.
V
- VREF 4.8 V - 2.5 V
V
= 5.75 V
G = OUT
=
VD
400 mV
(6)
Equation 7 calculates the gain-setting resistor value using the INA818 gain equation, Equation 1.
50 k:
50 k:
RG
10.5 k:
G 1 5.75 1
(7)
10.5 kΩ is a standard 0.1% resistor value that can be used in this design.
9.2.1.3 Application Curves
Figure 70 and Figure 71 show typical characteristic curves for the circuit in Figure 69.
C001
5
5
4
Output Voltage (V)
Output Voltage (V)
4
3
2
1
2
1
0
-10
-5
0
5
10
Input Voltage (V)
0
-20
-10
0
Input Current (mA)
Figure 70. PLC Output Voltage vs Input Voltage
30
3
10
20
C001
Figure 71. PLC Output Voltage vs Input Current
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Typical Applications (continued)
9.2.2 Resistance Temperature Detector Interface
Figure 72 illustrates a 3-wire interface circuit for resistance temperature detectors (RTDs). The circuit
incorporates analog linearization and has an output voltage range from 0 V to 5 V. The linearization technique
employed is described in the Analog linearization of resistance temperature detectors analog application journal.
Series and parallel combinations of standard 1% resistor values are used to achieve less than 0.02°C of error
over a 200°C temperature span.
15 V
NR
1 F
VIN
GND
-IN
RG
1.13
k
2.87
k
INA818
RG
+IN
Pt100 RTD
100
REF
100
k
100
+VS
4.99
k
VOUT
0 V at 0°C
5 V at 200°C
25 mV/°C
OUT
-VS
4.99
k
VOUT
1 F
1 F
REF5050
-15 V
105 k
1.18 k
Copyright © 2017, Texas Instruments Incorporated
5
0.018
4.5
0.016
4
0.014
3.5
0.012
Error (ƒC)
Output Voltage (V)
Figure 72. A 3-Wire Interface for RTDs With Analog Linearization
3
2.5
2
0.01
0.008
0.006
1.5
1
0.004
0.5
0.002
0
0
0
50
100
150
200
0
Temperature (°C)
50
100
150
Temperature (°C)
Figure 73. Transfer Function of a 3-Wire RTD Interface
200
C001
Figure 74. Temperature Error Over the Full Temperature
Range
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10 Power Supply Recommendations
The nominal performance of the INA818 is specified with a supply voltage of ±15 V and midsupply reference
voltage. The device can also be operated using power supplies from ±2.25 V (4.5 V) to ±18 V (36 V) and nonmidsupply reference voltages with excellent performance. Parameters that can vary significantly with operating
voltage and reference voltage are shown in the Typical Characteristics section.
11 Layout
11.1 Layout Guidelines
Attention to good layout practices is always recommended. For best operational performance of the device, use
good PCB layout practices, including:
• Take care to make sure that both input paths are well-matched for source impedance and capacitance to
avoid converting common-mode signals into differential signals. Even slight mismatch in parasitic capacitance
at the gain setting pins can degrade CMRR over frequency. For example, in applications that implement gain
switching using switches or PhotoMOS® relays to change the value of RG, select the component so that the
switch capacitance is as small as possible and most importantly so that capacitance mismatch between the
RG pins is minimized.
• Noise can propagate into analog circuitry through the power pins of the circuit as a whole and of the device
itself. Bypass capacitors reduce the coupled noise by providing low-impedance power sources local to the
analog circuitry.
– Connect low-ESR, 0.1-µF ceramic bypass capacitors between each supply pin and ground, placed as
close to the device as possible. A single bypass capacitor from V+ to ground is applicable for singlesupply applications.
• To reduce parasitic coupling, run the input traces as far away from the supply or output traces as possible. If
these traces cannot be kept separate, crossing the sensitive trace perpendicular is much better than in
parallel with the noisy trace.
• Place the external components as close to the device as possible. As shown in Figure 75, keeping RG close
to the pins minimizes parasitic capacitance.
• Keep the traces as short as possible.
32
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11.2 Layout Example
+V
C2
RG
RG
-IN
OUT
±VS
INA818
R3
REF
+IN
+VS
R2
R1
C1
Ground plane
removed at gain
resistor to minimize
parasitic capacitance
-V
Use ground pours for
shielding the input
signal pairs
R3
+V
GND
R1
Input traces routed
adjacent to each other
1
RG
RG
8
±IN
2
±IN
+VS
7
+IN
3
+IN
OUT
6
4
-VS
REF
5
R2
C2
GND
OUT
Low-impedance
connection for
reference terminal
C1
-V
Place bypass
capacitors as close to
IC as possible
Copyright © 2017, Texas Instruments Incorporated
Figure 75. Example Schematic and Associated PCB Layout
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12 Device and Documentation Support
12.1 Documentation Support
12.1.1 Related Documentation
For related documentation see the following:
• Texas Instruments, Universal Instrumentation Amplifier EVM user’s guide
• Texas Instruments, Comprehensive Error Calculation for Instrumentation Amplifiers application note
12.2 Receiving Notification of Documentation Updates
To receive notification of documentation updates, navigate to the device product folder on ti.com. In the upper
right corner, click on Alert me to register and receive a weekly digest of any product information that has
changed. For change details, review the revision history included in any revised document.
12.3 Community Resources
The following links connect to TI community resources. Linked contents are provided "AS IS" by the respective
contributors. They do not constitute TI specifications and do not necessarily reflect TI's views; see TI's Terms of
Use.
TI E2E™ Online Community TI's Engineer-to-Engineer (E2E) Community. Created to foster collaboration
among engineers. At e2e.ti.com, you can ask questions, share knowledge, explore ideas and help
solve problems with fellow engineers.
Design Support TI's Design Support Quickly find helpful E2E forums along with design support tools and
contact information for technical support.
12.4 Trademarks
E2E is a trademark of Texas Instruments.
Bluetooth is a registered trademark of Bluetooth SIG, Inc.
PhotoMOS is a registered trademark of Panasonic Electric Works Europe AG.
All other trademarks are the property of their respective owners.
12.5 Electrostatic Discharge Caution
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.
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.
12.6 Glossary
SLYZ022 — TI Glossary.
This glossary lists and explains terms, acronyms, and definitions.
13 Mechanical, Packaging, and Orderable Information
The following pages include mechanical, packaging, and orderable information. This information is the most
current data available for the designated devices. This data is subject to change without notice and revision of
this document. For browser-based versions of this data sheet, refer to the left-hand navigation.
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PACKAGE OPTION ADDENDUM
www.ti.com
10-Dec-2020
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)
(4/5)
(6)
INA818ID
ACTIVE
SOIC
D
8
75
RoHS & Green
NIPDAU
Level-2-260C-1 YEAR
-40 to 125
INA818
INA818IDR
ACTIVE
SOIC
D
8
2500
RoHS & Green
NIPDAU
Level-2-260C-1 YEAR
-40 to 125
INA818
(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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