ANALOG DEVICES AD8429 Service Manual
1 nV/√Hz Low Noise
FEATURES
Low noise
1 nV/√Hz input noise
45 nV/√Hz output noise
High accuracy dc performance (AD8429BRZ)
90 dB CMRR minimum (G = 1)
50 μV maximum input offset voltage
0.02% maximum gain accuracy (G = 1)
Excellent ac specifications
80 dB CMRR to 5 kHz (G = 1)
15 MHz bandwidth (G = 1)
1.2 MHz bandwidth (G = 100)
22 V/μs slew rate
THD: −130 dBc (1 kHz, G = 1)
Versa tile
±4 V to ±18 V dual supply
Gain set with a single resistor (G = 1 to 10,000)
Temperature range for specified performance
−40°C to +125°C
Instrumentation Amplifier
AD8429
PIN CONNECTION DIAGRAM
AD8429
–IN
R
R
+IN
G
G
1
2
3
4
(Not to Scale)
TOP VIEW
Figure 1.
8
+V
S
7
V
OUT
6
REF
5
–V
S
09730-001
APPLICATIONS
Medical instrumentation
Precision data acquisition
Microphone preamplification
Vibration analysis
GENERAL DESCRIPTION
The AD8429 is an ultralow noise, instrumentation amplifier
designed for measuring extremely small signals over a wide
temperature range (−40°C to +125°C).
The AD8429 excels at measuring tiny signals. It delivers ultralow
input noise performance of 1 nV/√Hz. The high CMRR of the
AD8429 prevents unwanted signals from corrupting the acquisition. The CMRR increases as the gain increases, offering high
rejection when it is most needed. The high performance pin
configuration of the AD8429 allows it to reliably maintain high
CMRR at frequencies well beyond those of typical instrumentation
amplifiers.
The AD8429 reliably amplifies fast changing signals. Its current
feedback architecture provides high bandwidth at high gain, for
example, 1.2 MHz at G = 100. The design includes circuitry to improve settling time after large input voltage transients. The AD8429
was designed for excellent distortion performance, allowing use in
demanding applications such as vibration analysis.
Gain is set from 1 to 10,000 with a single resistor. A reference
pin allows the user to offset the output voltage. This feature can
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.
be useful to shift the output level when interfacing to a single
supply signal chain.
The AD8429 performance is specified over the extended industrial
temperature range of −40°C to +125°C. It is available in an 8-lead
plastic SOIC package.
1000
100
Hz)
10
NOISE (nV/
1
0.1
1 10 100 1k 10k 100k
Figure 2. RTI Voltage Noise Spectral Density vs. Frequency
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781.329.4700 www.analog.com
Fax: 781.461.3113 ©2011 Analog Devices, Inc. All rights reserved.
FREQUENCY (Hz)
G = 1
G = 10
G = 100
G = 1k
09730-002
AD8429
TABLE OF CONTENTS
Features.............................................................................................. 1
Applications....................................................................................... 1
Pin Connection Diagram ................................................................ 1
General Description......................................................................... 1
Revision History ...............................................................................2
Specifications..................................................................................... 3
Absolute Maximum Ratings............................................................ 6
Thermal Resistance...................................................................... 6
ESD Caution.................................................................................. 6
Pin Configuration and Function Descriptions............................. 7
Typical Performance Characteristics............................................. 8
Theory of Operation ......................................................................15
REVISION HISTORY
4/11—Revision 0: Initial Version
Architecture ................................................................................ 15
Gain Selection............................................................................. 15
Reference Terminal.................................................................... 15
Input Voltage Range................................................................... 16
Layout .......................................................................................... 16
Input Bias Current Return Path ............................................... 17
Input Protection ......................................................................... 17
Radio Frequency Interference (RFI)........................................ 17
Calculating the Noise of the Input Stage................................. 18
Outline Dimensions....................................................................... 19
Ordering Guide .......................................................................... 19
Rev. 0 | Page 2 of 20
AD8429
SPECIFICATIONS
VS = ±15 V, V
Table 1.
A Grade B Grade
Parameter Test Conditions/Comments 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 dB
G = 10 100 110 dB
G = 100 120 130 dB
G = 1000 134 140 dB
CMRR at 5 kHz VCM = ±10 V
G = 1 76 80 dB
G = 10 90 90 dB
G = 100 90 90 dB
G = 1000 90 90 dB
VOLTAGE NOISE, RTI VIN+, VIN− = 0 V
Spectral Density1: 1 kHz
Input Voltage Noise, eni 1.0 1.0 nV/√Hz
Output Voltage Noise, eno 45 45 nV/√Hz
Peak to Peak: 0.1 Hz to 10 Hz
G = 1 2 2 μV p-p
G = 1000 100 100 nV p-p
CURRENT NOISE
Spectral Density: 1 kHz 1.5 1.5 pA/√Hz
Peak to Peak: 0.1 Hz to 10 Hz 100 100 pA p-p
VOLTAGE OFFSET2
Input Offset, V
Average TC 0.1 1 0.1 0.3 μV/°C
Output Offset, V
Average TC 3 10 3 10 μV/°C
Offset RTI vs. Supply (PSR) VS = ±5 V to ±15 V
G = 1 90 100 dB
G = 10 110 120 dB
G = 100 130 130 dB
G = 1000 130 130 dB
INPUT CURRENT
Input Bias Current 300 150 nA
Average TC 250 250 pA/°C
Input Offset Current 100 30 nA
Average TC 15 15 pA/°C
DYNAMIC RESPONSE
Small Signal Bandwidth: –3 dB
G = 1 15 15 MHz
G = 10 4 4 MHz
G = 100 1.2 1.2 MHz
G = 1000 0.15 0.15 MHz
= 0 V, TA = 25°C, G = 1, RL = 10 k, unless otherwise noted.
REF
VCM = ±10 V
150 50 μV
OSI
1000 500 μV
OSO
Rev. 0 | Page 3 of 20
AD8429
A Grade B Grade
Parameter Test Conditions/Comments Min Typ Max Min Typ Max Unit
Settling Time 0.01% 10 V step
G = 1 0.75 0.75 μs
G = 10 0.65 0.65 μs
G = 100 0.85 0.85 μs
G = 1000 5 5 μs
Settling Time 0.001% 10 V step
G = 1 0.9 0.9 μs
G = 10 0.9 0.9 μs
G = 100 1.2 1.2 μs
G = 1000 7 7 μs
Slew Rate
G = 1 to 100 22 22 V/μs
THD First five harmonics, f = 1 kHz,
= 2 kΩ, V
R
L
= 10 V p-p
OUT
G = 1 −130 −130 dBc
G = 10 −116 −116 dBc
G = 100 −113 −113 dBc
G = 1000 −111 −111 dBc
THD + N f = 1 kHz, RL = 2 kΩ, V
OUT
=
10 V p-p
G = 100 0.0005 0.0005 %
GAIN3 G = 1 + (6 kΩ/RG)
Gain Range 1 10000 1 10000 V/V
Gain Error V
= ±10 V
OUT
G = 1 0.05 0.02 %
G > 1 0.3 0.15 %
Gain Nonlinearity V
= −10 V to +10 V
OUT
G = 1 to 1000 RL = 10 kΩ 2 2 ppm
Gain vs. Temperature
G = 1 2 5 2 5 ppm/°C
G > 1 −100 −100 ppm/°C
INPUT
Impedance (Pin to Ground)4 1.5||3 1.5||3 GΩ||pF
Input Operating Voltage
Range
5
V
= ±4 V to ±18 V −VS + 2.8 +VS − 2.5 −VS + 2.8 +VS − 2.5 V
S
OUTPUT
Output Swing RL = 2 kΩ −VS + 1.8 +Vs − 1.2 −VS + 1.8 +Vs − 1.2 V
Over Temperature −VS + 1.9 +Vs − 1.3 −VS + 1.9 +Vs − 1.3 V
Output Swing RL = 10 kΩ −VS + 1.7 +Vs − 1.1 −VS + 1.7 +Vs − 1.1 V
Over Temperature −VS + 1.8 +Vs − 1.2 −VS + 1.8 +Vs − 1.2 V
Short-Circuit Current 35 35 mA
REFERENCE INPUT
RIN 10 10 kΩ
IIN V
+, VIN− = 0 V 70 70 μA
IN
Voltage Range −VS +VS V
Reference Gain to Output 1 1 V/V
Reference Gain Error 0.01 0.05 0.01 0.05 %
Rev. 0 | Page 4 of 20
AD8429
A Grade B Grade
Parameter Test Conditions/Comments Min Typ Max Min Typ Max Unit
POWER SUPPLY
Operating Range ±4 ±18 ±4 ±18 V
Quiescent Current 6.7 7 6.7 7 mA
T = 125°C 9 9 mA
TEMPERATURE RANGE
For Specified Performance −40 +125 −40 +125 °C
1
Total voltage noise = √(e
2
Total RTI VOS = (V
3
These specifications do not include the tolerance of the external gain setting resistor, RG. For G > 1, add RG errors to the specifications given in this table.
4
Differential and common-mode input impedance can be calculated from the pin impedance: Z
5
Input voltage range of the AD8429 input stage only. The input range can depend on the common-mode voltage, differential voltage, gain, and reference voltage.
See the section for more details. Input Voltage Range
OSI
) + (V
2
+ (eno/G)2 + e
ni
/G).
OSO
2
). See the Theory of Operation section for more information.
RG
DIFF
= 2(Z
); ZCM = Z
PIN
/2.
PIN
Rev. 0 | Page 5 of 20
AD8429
ABSOLUTE MAXIMUM RATINGS
Table 2.
Parameter Rating
Supply Voltage ±18 V
Output Short-Circuit Current Duration Indefinite
Maximum Voltage at –IN, +IN1 ±VS
Differential Input Voltage
Gain ≤ 4 ±VS
4 > Gain > 50 ±50 V/gain
Gain ≥ 50 ±1 V
Maximum Voltage at REF ±VS
Storage Temperature Range −65°C to +150°C
Specified Temperature Range −40°C to +125°C
Maximum Junction Temperature 140°C
ESD
Human Body Model 3.0 kV
Charge Device Model 1.5 kV
Machine Model 0.2 kV
1
For voltages beyond these limits, use input protection resistors. See the
Theory of Operation section for more information.
1
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 for extended periods may affect
device reliability.
THERMAL RESISTANCE
θJA is specified for a device in free air using a 4-layer JEDEC
printed circuit board (PCB).
Table 3.
Package θJA Unit
8-Lead SOIC 121 °C/W
ESD CAUTION
Rev. 0 | Page 6 of 20
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