ANALOG DEVICES AD8237 Service Manual
Instrumentation Amplifier
AD8237
Rev. PrA
Trademarks and registered trademarks are the property of their respective owners.
Fax: 781.461.3113 ©2012 Analog Devices, Inc. All rights reserved.
BW
1
+IN
2
–IN
3
–V
S
4
V
OUT
8
FB
7
REF
6
+V
S
5
AD8237
TOP VIEW
(Not to Scale)
+
–
–
+
10289-001
AD8421
AD8237
AD620
AD8237
AD8250
AD8221/AD8222
AD8231
AD621
AD8420
AD8251
AD8220/AD8224
AD8293
AD524
AD8235/AD8236
AD8253
AD8228
AD8553
AD526
AD627
AD8231
AD8295
AD8556
AD624
AD8226
AD8557
6
5
4
3
2
1
–1
0
0 1 2 3 4 5
INPUT COMMON MODE VOLTAGE (V)
OUTPUT VOLTAGE (V)
TRADITI ONAL IN-AMP
(RAIL-TO-RAIL OUT)
AD8237
10289-002
G = 100
V
S
= 5V
V
REF
= 2.5V
Preliminary Technical Data
FEATURES
Gain set with 2 external resistors
Can achieve low gain drift at all gains
Ideal for portable systems
Maximum supply current: 130 µA
Rail-to-rail input and output
Zero input crossover distortion
Designed for excellent dc performance
Minimum CMRR: 110 dB
Maximum offset voltage drift: 0.2 µV/°C
Maximum gain error: 0.005% (all gains)
Maximum gain drift: 0.5 ppm/°C (all gains)
Single-supply operation: 1.8 V to 5.5 V
8-lead MSOP package
APPLICATIONS
Bridge amplification
Pressure measurement
Medical instrumentation
Portable systems
Current measurement
GENERAL DESCRIPTION
The AD8237 is a micropower, zero drift, rail-to-rail input and
output instrumentation amplifier. The relative match of two
resistors sets any gain from 1 to 1000. The AD8237 has excellent
gain accuracy performance that can be preserved at any gain
with two ratio-matched resistors.
The AD8237 uses a novel indirect current-feedback architecture to
achieve a true rail-to-rail capability. Unlike conventional in-amps,
the AD8237 can fully amplify signals with common-mode voltage
at or even slightly beyond its supplies. This enables applications
with high common-mode voltages to use smaller supplies and
save power.
The AD8237 is an excellent choice for portable systems. With a
minimum supply voltage of 1.8 V, a 115 µA typical supply current,
and wide input range, the AD8237 makes full use of a limited
power budget, while still offering bandwidth and drift performance
suitable for bench-top systems.
The AD8237 is available in an 8-lead MSOP package. Performance
is specified over the full temperature range of −40°C to +125°C.
Micropower, Zero Drift, True Rail-to-Rail
PIN CONFIGURATION
Figure 1.
Table 1. Instrumentation Amplifiers by Category
General
Purpose
1
See www.analog.com for the latest instrumentation amplifiers.
Zero
Drift
Military
Grade Micropower
Figure 2. Input Common-Mode Voltage vs. Output Voltage, +V
1
Digital
Gain
= 5 V, G = 100
S
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.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781.329.4700
www.analog.com
AD8237 Preliminary Technical Data
TABLE OF CONTENTS
Features .............................................................................................. 1
Applications ....................................................................................... 1
General Description ......................................................................... 1
Pin Configuration ............................................................................. 1
Specifications ..................................................................................... 3
Absolute Maximum Ratings ............................................................ 7
Thermal Resistance ...................................................................... 7
ESD Caution .................................................................................. 7
Pin Configuration and Function Descriptions ............................. 8
Theory of Operation ........................................................................ 9
Architecture ................................................................................... 9
Setting the Gain ............................................................................ 9
Gain Accuracy ............................................................................ 10
Clock Feedthrough ..................................................................... 10
Input Voltage Range ................................................................... 10
Input Protection ......................................................................... 10
Filtering Radio Frequency Interference .................................. 11
Using the Reference Pin ............................................................ 11
Layout .......................................................................................... 11
Input Bias Current Return Path ............................................... 12
Outline Dimensions ....................................................................... 13
Rev. PrA | Page 2 of 13
Preliminary Technical Data AD8237
COMMON-MODE REJECTION RATIO (CMRR)
VCM = 0.2 V to 4.8 V
CMRR at 1 kHz
80
dB
INPUTS1
Valid for REF and FB pair, as well as +IN and −IN
Small Signal Bandwidth
–3 dB
SPECIFICATIONS
+VS = +5 V, − VS = 0 V, V
otherwise noted.
Table 2.
Parameter Test Conditions/Comments Min Typ Max Unit
CMRR DC to 60 Hz
G = 1, G = 10 110 120 dB
G = 100, G = 1000 120 140 dB
Over Temperature (G = 1) TA = −40°C to +125°C 106 dB
NOISE
Voltage Noise
Spectral Density f = 1 kHz 70 nV/√Hz
Peak to Peak f = 0.1 Hz to 10 Hz 1.5 µV p-p
Current Noise
Spectral Density f = 1 kHz 100 fA/√Hz
Peak to Peak f = 0.1 Hz to 10 Hz TBD pA p-p
VOLTAGE OFFSET
Offset 60 µV
Average Temperature Coefficient TA = −40°C to +125°C 0.2 µV/°C
Offset RTI vs. Supply (PSR) 106 dB
= 2.5 V, V
REF
= 2.5 V, TA = 25°C, G = 1 to 1000, RL = 10 kΩ to ground, specifications referred to input, unless
CM
Input Bias Current TA = +25°C 0.5 nA
TA = −40°C to +85°C 1 nA
TA = +125°C 15 nA
Input Offset Current TA = +25°C 0.5 nA
TA = −40°C to +85°C 1 nA
TA = +125°C 5 nA
Input Impedance
Differential 200||5 MΩ||pF
Common Mode 600||10 MΩ||pF
Differential Input Operating Voltage TA = –40°C to +125°C −3.8 3.8 V
Input Operating Voltage (+IN, −IN, or REF) TA = +25°C −VS − 0.3 +VS + 0.3 V
DYNAMIC RESPONSE
Low Bandwidth Mode Pin 1 connected to −VS
G = 1 200 kHz
G = 10 20 kHz
G = 100 2 kHz
G = 1000 0.2 kHz
High Bandwidth Mode Pin 1 connected to +VS
G = 10 100 kHz
G = 100 10 kHz
G = 1000 1 kHz
T
= –40°C to +125°C −VS − 0.2 +VS + 0.2 V
A
Rev. PrA | Page 3 of 13
AD8237 Preliminary Technical Data
G = 100
440 µs
Gain vs. Temperature
TA = −40°C to +125°C
0.5
ppm/°C
Parameter Test Conditions/Comments Min Typ Max Unit
Settling Time 0.01% 4 V output step
Low Bandwidth Mode Pin 1 connected to −VS
G = 1 80 µs
G = 10 100 µs
G = 1000 4 ms
High Bandwidth Mode Pin 1 connected to +VS
G = 10 80 µs
G = 100 100 µs
G = 1000 820 µs
Slew Rate
Low Bandwidth Mode 0.05 V/µs
High Bandwidth Mode 0.15 V/µs
EMI Filter Frequency 6 MHz
GAIN2 G = 1 + (R2/R1)
Gain Range3 1 1000 V/V
Gain Error V
Gain Error vs. V
CM
= 0.2 V to 3.3 V, G = 1 to G = 1000 0.005 %
OUT
TBD ppm
Gain Nonlinearity V
= 0.2 V to 4.8 V, RL = 10 kΩ to ground
OUT
G = 1, G = 10 3 ppm
G = 100 6 ppm
G = 1000 10 ppm
OUTPUT
Output Swing
RL = 10 kΩ to midsupply
TA = +25°C −VS + 0.05 +VS − 0.05 V
TA = −40°C to 125°C −VS + 0.07 +VS − 0.07 V
RL = 100 kΩ to midsupply
TA = +25°C −VS + 0.02 +VS − 0.02 V
TA = −40°C to 125°C −VS + 0.03 +VS − 0.03 V
Short-Circuit Current 4 mA
POWER SUPPLY
Operating Range 1.8 5.5 V
Quiescent Current TA = +25°C 115 130 µA
TA = −40°C to +125°C 150 µA
TEMPERATURE RANGE
Specified −40 +125 °C
1
Specifications apply to input voltages between 0 V and 5 V. When measuring voltages beyond the supplies, there is additional offset error, bias currents increase and
input impedance decrease, especially at higher temperatures.
2
For G > 1, errors from the external resistors, R1 and R2, must be added to these specifications, including error from the FB pin bias current.
3
The AD8237 has only been characterized for gains of 1 to 1000; however, higher gains are possible.
Rev. PrA | Page 4 of 13
Loading...