Analog Devices AD8221 a Datasheet
+
Precision Instrumentation Amplifier
FEATURES
Available in space-saving MSOP package
Gain set with 1 external resistor (gain range 1 to 1000)
Wide power supply range: ±2.3 V to ±18 V
Temperature range for specified performance:
–40°C to +85°C
Operational up to 125°C
EXCELLENT AC SPECIFICATONS
80 dB min CMRR to 10 kHz ( G = 1)
825 kHz –3 dB bandwidth (G = 1)
2 V/µs slew rate
LOW NOISE
8 nV/√Hz, @ 1 kHz, max input voltage noise
0.25 µV p-p input noise (0.1 Hz to 10 Hz)
HIGH ACCURACY DC PERFORMANCE (AD8221BR)
90 dB min CMRR (G = 1)
25 µV max input offset voltage
0.3 µV/°C max input offset drift
0.4 nA max input bias current
APPLICATIONS
Weigh scales
Industrial process controls
Bridge amplifiers
Precision data acquisition systems
Medical instrumentation
Strain gages
Transducer interfaces
GENERAL DESCRIPTION
The AD8221 is a gain programmable, high performance instrumentation amplifier that delivers the industry’s highest CMRR
over frequency. The CMRR of instrumentation amplifiers on
the market today falls off at 200 Hz. In contrast, the AD8221
maintains a minimum CMRR of 80 dB to 10 kHz for all grades
at G = 1. High CMRR over frequency allows the AD8221 to
reject wideband interference and line harmonics, greatly
simplifying filter requirements. Possible applications include
precision data acquisition, biomedical analysis, and aerospace
instrumentation.
Low voltage offset, low offset drift, low gain drift, high gain
accuracy, and high CMRR make this part an excellent choice in
applications that demand the best dc performance possible,
such as bridge signal conditioning.
1
AD8221
CONNECTION DIAGRAM
1
–IN
2
R
G
3
R
G
4
IN
AD8221
TOP VIEW
Figure 1. SOIC and MSOP Connection Diagram
120
110
100
90
80
CMRR (dB)
70
60
50
40
10010 1k 10k 100k
FREQUENCY (Hz)
Figure 2. Typical CMRR vs. Frequency for G = 1
Programmable gain affords the user design flexibility. A single
resistor sets the gain from 1 to 1000. The AD8221 operates on
both single and dual supplies, and is well suited for applications
where ±10 V input voltages are encountered.
The AD8221 is available in low cost 8-lead SOIC and MSOP
packages, both of which offer the industry’s best performance.
The MSOP requires half the board space of the SOIC, making it
ideal for multichannel or space-constrained applications.
Performance is specified over the entire industrial temperature
range of –40°C to +85°C for all grades. Furthermore, the
AD8221 is operational from –40°C to +125°C
1
See Typical Performance Curves for expected operation from 85°C to 125°C.
8
+V
S
7
V
OUT
6
REF
5
–V
S
AD8221
COMPETITOR 1
COMPETITOR 2
03149-0-001
1
.
03149-0-002
Rev. A
Information furnished by Analog Devices is believed to be accurate and reliable.
However, no responsibility is assumed by Analog Devices for its use, nor for any
infringements of patents or other rights of third parties that may result from its use.
Specifications subject to change without notice. No license is granted by implication
or otherwise under any patent or patent rights of Analog Devices. Trademarks and
registered trademarks are the property of their respective owners.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781.329.4700 www.analog.com
Fax: 781.326.8703 © 2003 Analog Devices, Inc. All rights reserved.
AD8221
TABLE OF CONTENTS
Specifications..................................................................................... 3
Absolute Maximum Ratings............................................................ 5
ESD Caution.................................................................................. 5
Typical Performance Characteristics............................................. 6
Theory of Operation ......................................................................13
Gain Selection............................................................................. 14
Layout........................................................................................... 14
Reference Terminal ....................................................................15
Power Supply Regulation and Bypassing ................................15
Input Bias Current Return Path................................................15
Input Protection ......................................................................... 15
RF Interference........................................................................... 16
Precision Strain Gage................................................................. 16
Conditioning ±10 V Signals for a +5 V Differential Input
ADC ............................................................................................. 17
AC-Coupled Instrumentation Amplifier ................................ 17
Outline Dimensions....................................................................... 18
Ordering Guide .......................................................................... 18
REVISION HISTORY
Revision A
11/03—Data Sheet Changed from Rev. 0 to Rev. A
Change Page
Changes to Features...............................................................................1
Changes to Specifications section .......................................................4
Change to Theory of Operation section...........................................13
Change to Gain Selection section......................................................14
Rev. A | Page 2 of 20
AD8221
SPECIFICATIONS
Table 1. VS = ±15 V, V
Parameter Conditions Min Typ Max Min Typ Max Min Typ Max Unit
COMMON-MODE
REJECTION RATIO (CMRR)
CMRR DC to 60 Hz with
1 kΩ Source Imbalance
G = 1 80 90 80 dB
G = 10 100 110 100 dB
G = 100 120 130 120 dB
G = 1000 130 140 130 dB
CMRR at 10 kHz VCM = –10 V to +10 V
G = 1 80 80 80 dB
G = 10 90 100 90 dB
G = 100 100 110 100 dB
G = 1000 100 110 100 dB
NOISE
Voltage Noise, 1 kHz
Input Voltage Noise, eNI V
Output Voltage Noise, eNO 75 75 75 nV/√Hz
RTI f = 0.1 Hz to 10 Hz
G = 1 2 2 2 µV p-p
G = 10 0.5 0.5 0.5 µV p-p
G = 100 to 1000 0.25 0.25 0.25 µV p-p
Current Noise f = 1 kHz 40 40 40 fA/√Hz
f = 0.1 Hz to 10 Hz 6 6 6 pA p-p
VOLTAGE OFFSET1
Input Offset, V
V
OSI
Over Temperature T = –40°C to +85°C 86 45 135 µV
Average TC 0.4 0.3 0.9 µV/°C
Output Offset, V
OSO
Over Temperature T = –40°C to +85°C 0.66 0.45 1.00 mV
Average TC 6 5 9 µV/°C
Offset RTI vs. Supply (PSR) VS = ±2.3 V to ±18 V
G = 1 90 110 94 110 90 100 dB
G = 10 110 120 114 130 100 120 dB
G = 100 124 130 130 140 120 140 dB
G = 1000 130 140 140 150 120 140 dB
INPUT CURRENT
Input Bias Current 0.5 1.5 0.2 0.4 0.5 2 nA
Over Temperature T = –40°C to +85°C 2.0 1 3 nA
Average TC 1 1 3 pA/°C
Input Offset Current 0.2 0.6 0.1 0.4 0.3 1 nA
Over Temperature T = –40°C to +85°C 0.8 0.6 1.5 nA
Average TC 1 1 3 pA/°C
REFERENCE INPUT
RIN 20 20 20 kΩ
IIN V
Voltage Range –VS +VS –VS +VS –VS +VS V
Gain to Output
POWER SUPPLY
Operating Range VS = ±2.3 V to ±18 V ±2.3 ±18 ±2.3 ±18 ±2.3 ±18 V
Quiescent Current 0.9 1 0.9 1 0.9 1 mA
Over Temperature T = –40°C to +85°C 1 1.2 1 1.2 1 1.2 mA
= 0 V, TA = +25°C, G = 1, RL = 2 kΩ, unless otherwise noted
REF
AR Grade BR Grade ARM Grade
VCM = –10 V to +10 V
RTI noi se = √
, V
IN+
= ±5 V to ±15 V 60 25 70 µV
S
V
= ±5 V to ±15 V 300 200 600 µV
S
, V
IN+
e
NI
, V
= 0 8 8 8 nV/√Hz
IN–
REF
, V
= 0 50 60 50 60 50 60 µA
IN–
REF
2
+ (eNO/G)
2
1 ± 0.0001 1 ± 0.0001 1 ± 0.0001
V/V
Rev. A | Page 3 of 20
AD8221
AR Grade BR Grade ARM Grade
Parameter Conditions Min Typ Max Min Typ Max Min Typ Max Unit
DYNAMIC RESPONSE
Small Signal –3 dB
Bandwidth
G = 1 825 825 825 kHz
G = 10 562 562 562 kHz
G = 100 100 100 100 kHz
G = 1000 14.7 14.7 14.7 kHz
Settling Time 0.01% 10 V Step
G = 1 to 100 10 10 10 µs
G = 1000 80 80 80 µs
Settling Time 0.001% 10 V Step
G = 1 to 100 13 13 13 µs
G = 1000 110 110 110 µs
Slew Rate G = 1 1.5 2 1.5 2 1.5 2 V/µs
G = 5–100 2 2.5 2 2.5 2 2.5 V/µs
GAIN G = 1 + (49.4 kΩ/RG)
Gain Range 1 1000 1 1000 1 1000 V/V
Gain Error V
G = 1 0.03 0.02 0.1 %
G = 10 0.3 0.15 0.3 %
G = 100 0.3 0.15 0.3 %
G = 1000 0.3 0.15 0.3 %
Gain Nonlinearity V
G = 1 to 10 RL = 10 kΩ 3 10 3 10 5 15 ppm
G = 100 RL = 10 kΩ 5 15 5 15 7 20 ppm
G = 1000 RL = 10 kΩ 10 40 10 40 10 50 ppm
G = 1 to 100 RL = 2 kΩ 10 95 10 95 15 100 ppm
Gain vs. Temperature
G = 1 3 10 2 5 3 10 ppm/°C
2
G > 1
INPUT
Input Impedance
Differential 100||2 100||2 100||2 GΩ||pF
Common Mode 100||2 100||2 100||2 GΩ||pF
Input Operating
Voltage Range
3
Over Temperature T = –40°C to +85°C –VS + 2.0 +VS – 1.2 –VS + 2.0 +VS – 1.2 –VS + 2.0 +VS – 1.2 V
Input Operating
Voltage Range
Over Temperature T = –40°C to +85°C –VS + 2.0 +VS – 1.2 –VS + 2.0 +VS – 1.2 –VS + 2.0 +VS – 1.2 V
OUTPUT RL = 10 kΩ
Output Swing VS = ±2.3 V to ±5 V –VS + 1.1 +VS – 1.2 –VS + 1.1 +VS – 1.2 –VS + 1.1 +VS – 1.2 V
Over Temperature T = –40°C to +85°C –VS + 1.4 +Vs – 1.3 –VS + 1.4 +Vs – 1.3 –VS + 1.4 +Vs – 1.3 V
Output Swing VS = ±5 V to ±18 V –VS + 1.2 +VS – 1.4 –VS + 1.2 +VS – 1.4 –VS + 1.2 +VS – 1.4 V
Over Temperature T = –40°C to +85°C –VS + 1.6 +VS – 1.5 –VS + 1.6 +VS – 1.5 –VS + 1.6 +VS – 1.5 V
Short-Circuit Current 18 18 18 mA
TEMPERATURE RANGE
Specified Performance –40 +85 –40 +85 –40 +85 °C
Operational
4
1
Total RTI VOS = (V
2
Does not include the effects of external resistor RG.
3
One input grounded. G = 1.
4
See Typical Performance Curves for expected operation between 85°C to 125°C.
OSI
) + (V
±10 V
OUT
= –10 V to +10 V
OUT
–50 –50 –50 ppm/°C
VS = ±2.3 V to ±5 V –VS + 1.9 +VS – 1.1 –VS + 1.9 +VS – 1.1 –VS + 1.9 +VS – 1.1 V
VS = ±5 V to ±18 V –VS + 1.9 +VS – 1.2 –VS + 1.9 +VS – 1.2 –VS + 1.9 +VS – 1.2 V
–40 +125 –40 +125 –40 +125 °C
/G).
OSO
Rev. A | Page 4 of 20
AD8221
ABSOLUTE MAXIMUM RATINGS
Table 2. AD8221 Absolute Maximum Ratings
Parameter Rating
Supply Voltage ±18 V
Internal Power Dissipation 200 mW
Output Short Circuit Current Indefinite
Input Voltage (Common-Mode) ±V
Differential Input Voltage ±Vs
Storage Temperature –65°C to +150°C
Operational* Temperature Range –40°C to +125°C
*Temperature range for specified performance is –40°C to +85°C. See Typical
Performance Curves for expected operation from +85°C to +125°C.
S
ESD CAUTION
ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily accumulate on the human body and test equipment and can discharge without detection. Although this
product features proprietary ESD protection circuitry, permanent damage may occur on devices
subjected to high energy electrostatic discharges. Therefore, proper ESD precautions are recommended to avoid performance degradation or loss of functionality.
Stresses above those listed under Absolute Maximum Ratings
may cause permanent damage to the device. This is a stress
rating only; functional operation of the device at these or any
other conditions above those indicated in the operational
section of this specification is not implied. Exposure to absolute
maximum rating conditions may affect device reliability.
Specification is for device in free air:
SOIC θ
MSOP θ
(4 Layer JEDEC Board) = 121°C/W.
JA
(4 Layer JEDEC Board) = 135°C/W.
JA
Rev. A | Page 5 of 20
AD8221
TYPICAL PERFORMANCE CHARACTERISTICS
(@+25°C, VS = ±15 V, RL = 10 kΩ, unless otherwise noted.)
1600
3500
1400
1200
1000
800
UNITS
600
400
200
2400
2100
1800
1500
1200
UNITS
900
600
300
0
0–50–100–150 50 100 150
CMR (µV/V)
Figure 3. Typical Distribution for CMR (G = 1)
03149-0-003
3000
2500
2000
UNITS
1500
1000
500
0
INPUT OFFSET CURRENT (nA)
0–0.3–0.6–0.9 0.3 0.6 0.9
Figure 6. Typical Distribution of Input Offset Current
15
10
5
0
–5
–10
INPUT COMMON-MODE VOLTAGE (V)
VS = ±5V
VS = ±15V
03149-0-006
0
INPUT OFFSET VOLTAGE (µV)
0–20–40–60 204060
Figure 4. Typical Distribution of Input Offset Voltage
3000
2500
2000
1500
UNITS
1000
500
0
INPUT BIAS CURRENT (nA)
0–0.5–1.0–1.5 0.5 1.0 1.5
Figure 5. Typical Distribution of Input Bias Current
03149-0-004
03149-0-005
Rev. A | Page 6 of 20
–15
–5 0–15 –10 5 10 15
OUTPUT VOLTAGE (V)
Figure 7. Input Common-Mode Range vs. Output Voltage, G = 1
15
10
VS = ±15V
5
0
–5
–10
INPUT COMMON-MODE VOLTAGE (V)
–15
–5 0–15 –10 5 10 15
OUTPUT VOLTAGE (V)
VS = ±5V
Figure 8. Input Common-Mode Range vs. Output Voltage, G = 100
03149-0-007
03149-0-008
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