ANALOG DEVICES AD8231 Service Manual

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A

Zero Drift, Digitally Programmable

FEATURES

Digitally/pin programmable gain

G = 1, 2, 4, 8, 16, 32, 64, 128

Specified from −40°C to +125°C

50 nV/°C maximum input offset drift
10 ppm/°C maximum gain drift

Excellent dc performance

80 dB minimum CMR, G = 1
15 µV maximum input offset voltage
500 pA maximum bias current

0.7 µV p-p noise (0.1 Hz to 10 Hz)

Good ac performance

2.7 MHz bandwidth, G = 1

1.1 V/s slew rate
Rail-to-rail input and output
Shutdown/multiplex
Extra op amp
Single supply range: 3 V to 6 V
Dual supply range: ±1.5 V to ±3 V

APPLICATIONS

Pressure and strain transducers
Thermocouples and RTDs
Programmable instrumentation
Industrial controls
Weigh scales

GENERAL DESCRIPTION

The AD8231 is a low drift, rail-to-rail, instrumentation ampli­fier with software programmable gains of 1, 2, 4, 8, 16, 32, 64, or

128. The gains are programmed via digital logic or pin
strapping.

The AD8231 is ideal for applications that require precision
performance over a wide temperature range, such as industrial
temperature sensing and data logging. Because the gain setting
resistors are internal, maximum gain drift is only 10 ppm/°C.
Because of the auto-zero input stage, maximum input offset is
15 µV and maximum input offset drift is just 50 nV/°C. CMRR
is also guaranteed over temperature at 80 dB for G = 1, increas­ing to 110 dB at higher gains.

Instrumentation Amplifier

AD8231

FUNCTIONAL BLOCK DIAGRAM

A216A115A014CS

13

1

NC

LOGIC

2

–INA

+IN

NC

3

4

IN-AMP

AD8231

5

SDN

OP

AMP

7

6

+INB

Figure 1.

–INB

Table 1. Instrumentation/Difference Amplifiers by Category

High
Performance

AD8221 AD6231AD628 AD620 AD6271AD8231

1

AD8220
AD8222 AD524 AD8251

1

AD8224

AD624 AD8556
AD8557

1

Rail-to-rail output.

Low
Cost

AD85531AD629 AD621 AD8250

AD526 AD8555

High
Voltage

Mil
Grade

The AD8231 also includes an uncommitted op amp that can be
used for additional gain, differential signal driving or filtering.
Like the in-amp, the op amp has an auto-zero architecture, rail­to-rail input, and rail-to-rail output.

The AD8231 includes a shutdown feature that reduces current
to a maximum of 1 µA. In shutdown, both amplifiers also have
a high output impedance. This allows easy multiplexing of
multiple amplifiers without additional switches.

The AD8231 is specified over the extended industrial tempera­ture range of −40°C to +125°C. It is available in a 4 mm × 4 mm
16-lead LFCSP (chip scale).

12

+V

S

11

–V

S

10

OUTA

9

REF

8

OUTB

Low
Power

06586-001

Digital
Gain

1

1

1

1

Rev. 0

Information furnished by Analog Devices is believed to be accurate and reliable. However, no
responsibility is assumed by Anal og Devices for its use, nor for any infringements of patents or ot her
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: [phone] www.analog.com
Fax: [phone] ©2007 Analog Devices, Inc. All rights reserved.

AD8231

TABLE OF CONTENTS

Features.............................................................................................. 1

Applications....................................................................................... 1

Functional Block Diagram .............................................................. 1

General Description ......................................................................... 1

Revision History ............................................................................... 2

Specifications..................................................................................... 3

Absolute Maximum Ratings............................................................ 7

Thermal Resistance ...................................................................... 7

ESD Caution.................................................................................. 7

Pin Configuration and Function Descriptions............................. 8

Typical Performance Characteristics ............................................. 9

Instrumentation Amplifier Performance Curves..................... 9

Operational Amplifier Performance Curves ..........................12

Performance Curves Valid for Both Amplifiers..................... 13

Theory of Operation ...................................................................... 14

Amplifier Architecture .............................................................. 14

Gain Selection............................................................................. 14

Reference Terminal .................................................................... 14

Layout .......................................................................................... 15

Input Bias Current Return Path ............................................... 15

RF Interference........................................................................... 15

Common-Mode Input Voltage Range..................................... 16

Applications Information.............................................................. 17

Differential Output .................................................................... 17

Multiplexing................................................................................ 17

Outline Dimensions....................................................................... 18

Ordering Guide .......................................................................... 18

REVISION HISTORY

5/07—Revision 0: Initial Version

Rev. 0 | Page 2 of 20

AD8231

SPECIFICATIONS

VS = 5 V, V

Table 2.

Parameter Conditions Min Typ Max Unit
INSTRUMENTATION AMPLIFIER

OFFSET VOLTAGE VOS RTI = V

Input Offset, V

Average Temperature Drift TA = −40°C to +125°C 0.01 0.05 μV/°C

Output Offset, V

Average Temperature Drift TA = −40°C to +125°C 0.05 0.5 μV/°C

INPUT CURRENTS

Input Bias Current 250 500 pA

T

Input Offset Current 20 100 pA
T
GAINS 1, 2, 4, 8, 16, 32, 64, 128

Gain Error

G = 1 0.05 %
G = 2 to 128 0.8 %

Gain Drift

G = 1 3 10 ppm/°C
G = 2 to 128 3 10 ppm/°C

CMRR

G = 1 80 dB

G = 2 86 dB

G = 4 92 dB

G = 8 98 dB

G = 16 104 dB

G = 32 110 dB

G = 64 110 dB

G = 128 110 dB
NOISE en = √(e

Input Voltage Noise, eni f = 1 kHz 32 nV/√Hz

f = 1 kHz, TA = −40°C 27 nV/√Hz

f = 1 kHz, TA = 125°C 39 nV/√Hz

f = 0.1 Hz to 10 Hz, 0.7 μV p-p

Output Voltage Noise, eno f = 1 kHz 58 nV/√Hz
f = 1 kHz, TA = −40°C 50 nV/√Hz
f = 1 kHz, TA = 125°C 70 nV/√Hz
f = 0.1 Hz to 10 Hz 1.1 μV p-p
OTHER INPUT CHARACTERISTICS

Common-Mode Input Impedance 10||5 GΩ||pF

Power Supply Rejection Ratio 100 110 dB

Input Operating Voltage Range 0.05 4.95 V
REFERENCE INPUT

Input Impedance

Voltage Range

= 2.5 V, G = 1, RL = 10 kΩ, TA = 25°C, unless otherwise noted.

REF

+ V

OSI

4 15 μV

OSI

15 30 μV

OSO

= −40°C to +125°C 5 nA

A

= −40°C to +125°C 0.5 nA

A

2

+ (eno/G)2), V

ni

/G

OSO

, V

IN+

= 2.5 V

IN−

28 kΩ

−0.2 +5.2 V

Rev. 0 | Page 3 of 20

AD8231

Parameter Conditions Min Typ Max Unit

DYNAMIC PERFORMANCE

Bandwidth

G = 1 2.7 MHz
G = 2 2.5 MHz

Gain Bandwidth Product

G = 4 to 128 7 MHz

Slew Rate 1.1 V/μs

OUTPUT CHARACTERISTICS

Output Voltage High RL = 100 kΩ to ground 4.9 4.94 V
R

= 10 kΩ to ground 4.8 4.88 V

L

Output Voltage Low RL = 100 kΩ to 5 V 60 100 mV
R

= 10 kΩ to 5 V 80 200 mV

L

Short-Circuit Current 70 mA

DIGITAL INTERFACE

Input Voltage Low TA = −40°C to +125°C 1.0 V
Input Voltage High TA = −40°C to +125°C 4.0 V

T

Setup Time to CS high
Hold Time after CS high

OPERATIONAL AMPLIFIER

= −40°C to +125°C 50 ns

A

T

= −40°C to +125°C 20 ns

A

INPUT CHARACTERISTICS

Offset Voltage, VOS 5 15 μV

Temperature Drift TA = −40°C to +125°C 0.01 0.06 uV/°C
Input Bias Current 250 500 pA
T

= −40°C to +125°C 5 nA

A

Input Offset Current 20 100 pA
T

= −40°C to +125°C 0.5 nA

A

Input Voltage Range 0.05 4.95 V
Open-Loop Gain 100 120 V/mV
Common-Mode Rejection Ratio 100 120 dB
Power Supply Rejection Ratio 100 115 dB
Voltage Noise Density 20 nV/√Hz
Voltage Noise f = 0.1 Hz to 10 Hz 0.4 μV p-p

DYNAMIC PERFORMANCE

Gain Bandwidth Product 1 MHz
Slew Rate 0.5 V/μs

OUTPUT CHARACTERISTICS

Output Voltage High RL = 100 kΩ to ground 4.9 4.96 V
R

= 10 kΩ to ground 4.8 4.92 V

L

Output Voltage Low RL = 100 kΩ to 5 V 60 100 mV
R

= 10 kΩ to 5 V 80 200 mV

L

Short-Circuit Current 70 mA

BOTH AMPLIFIERS
POWER SUPPLY

Quiescent Current 4 5 mA
Quiescent Current (Shutdown) 0.01 1 μA

Rev. 0 | Page 4 of 20

AD8231

VS = 3.0 V, V

Table 3.

Parameter Conditions Min Typ Max Unit
INSTRUMENTATION AMPLIFIER

OFFSET VOLTAGE VOS RTI = V

Input Offset, V
Average Temperature Drift 0.01 0.05 μV/°C
Output Offset, V
Average Temperature Drift 0.05 0.5 μV/°C

INPUT CURRENTS

Input Bias Current 250 500 pA
T
Input Offset Current 20 100 pA
T

GAINS 1, 2, 4, 8, 16, 32, 64, 128

Gain Error

G = 1 0.05 %
G = 2 to 128 0.8 %

Gain Drift

G = 1 3 10 ppm/°C
G = 2 to 128 3 10 ppm/°C

CMRR

G = 1 80 dB
G = 2 86 dB
G = 4 92 dB
G = 8 98 dB
G = 16 104 dB
G = 32 110 dB
G = 64 110 dB
G = 128 110 dB

NOISE

Input Voltage Noise, eni f = 1 kHz 40 nV/√Hz
f = 1 kHz, TA = −40°C 35 nV/√Hz
f = 1 kHz, TA = 125°C 48 nV/√Hz
f = 0.1 Hz to 10 Hz 0.8 μV p-p
Output Voltage Noise, eno f = 1 kHz 72 nV/√Hz
f = 1 kHz, TA = −40°C 62 nV/√Hz
f = 1 kHz, TA = 125°C 83 nV/√Hz
f = 0.1 Hz to 10 Hz 1.4 μV p-p

OTHER INPUT CHARACTERISTICS

Common-Mode Input Impedance 10||5 GΩ||pF
Power Supply Rejection Ratio 100 110 dB
Input Operating Voltage Range 0.05 2.95 V

REFERENCE INPUT

Input Impedance
Voltage Range

= 1.5 V, TA = 25°C, G = 1, RL = 10 kΩ, unless otherwise noted.

REF

+ V

OSI

4 15 μV

OSI

15 30 μV

OSO

= −40°C to +125°C 5 nA

A

= −40°C to +125°C 0.5 nA

A

2

= √(e

e

n

V

IN+

+ (eno/G)2)

ni

, V

= 2.5 V, TA = 25°C

IN−

/G

OSO

28 kΩ||pF

−0.2 +3.2 V

Rev. 0 | Page 5 of 20

AD8231

Parameter Conditions Min Typ Max Unit

DYNAMIC PERFORMANCE

Bandwidth

G = 1 2.7 MHz

G = 2 2.5 MHz
Gain Bandwidth Product

G = 4 to 128 7 MHz
Slew Rate 1.1 V/μs

OUTPUT CHARACTERISTICS

Output Voltage High RL = 100 kΩ to ground 2.9 2.94 V
R
Output Voltage Low RL = 100 kΩ to 3 V 60 100 mV
R
Short-Circuit Current 70 mA

DIGITAL INTERFACE

Input Voltage Low TA = −40°C to +125°C 0.7 V
Input Voltage High TA = −40°C to +125°C 2.3 V

Setup Time to CS high
Hold Time after CS high

OPERATIONAL AMPLIFIER
INPUT CHARACTERISTICS

Offset Voltage, VOS 5 15 μV
Temperature Drift TA = −40°C to +125°C 0.01 0.06 μV/°C
Input Bias Current 250 500 pA
T
Input Offset Current 20 100 pA
T
Input Voltage Range 0.05 2.95 V
Open-Loop Gain 100 120 V/mV
Common-Mode Rejection Ratio 100 120 dB
Power Supply Rejection Ratio 100 115 dB
Voltage Noise Density 27 nV/√Hz
Voltage Noise f = 0.1 Hz to 10 Hz 0.6 μV p-p

DYNAMIC PERFORMANCE

Gain Bandwidth Product 1 MHz
Slew Rate 0.5 V/μs

OUTPUT CHARACTERISTICS

Output Voltage High RL = 100 kΩ to ground 2.9 2.96 V
R
Output Voltage Low RL = 100 kΩ to 3 V 60 100 mV
R
Short-Circuit Current 70 mA

BOTH AMPLIFIERS
POWER SUPPLY

Quiescent Current 3.5 4.5 mA
Quiescent Current (Shutdown) 0.01 1 μA

= 10 kΩ to ground 2.8 2.88 V

L

= 10 kΩ to 3 V 80 200 mV

L

TA = −40°C to +125°C 60 ns
TA = −40°C to +125°C 20 ns

= −40°C to +125°C 5 nA

A

= −40°C to +125°C 0.5 nA

A

= 10 kΩ to ground 2.8 2.82 V

L

= 10 kΩ to 3 V 80 200 mV

L

Rev. 0 | Page 6 of 20