AD549 Analog Devices, AD549 Datasheet

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AD549

Manufacturer Part Number
AD549
Description
Ultralow Input-Bias Current Operational Amplifier
Manufacturer
Analog Devices
Datasheet

Specifications of AD549

-3db Bandwidth
1MHz
Slew Rate
3V/µs
Vos
500µV
Ib
150fA
# Opamps Per Pkg
1
Input Noise (nv/rthz)
35nV/rtHz
Vcc-vee
10V to 36V
Isy Per Amplifier
700µA
Packages
TO-X

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FEATURES
Ultralow input bias current
Input bias current guaranteed over the common-mode
Low offset voltage
Low offset drift
Low power
4 μV p-p over 0.1 Hz to 10 Hz
MIL-STD-883B parts available
APPLICATIONS
Electrometer amplifier
Photodiode preamp
pH electrode buffer
Vacuum ion gauge measurement
GENERAL DESCRIPTION
The AD549 is a monolithic electrometer operational amplifier
with very low input bias current. Input offset voltage and input
offset voltage drift are laser trimmed for precision performance.
The ultralow input current of the part is achieved with Topgate™
JFET technology, a process development exclusive to Analog
Devices, Inc. This technology allows fabrication of extremely
low input current JFETs compatible with a standard junction
isolated bipolar process. The 10
which results from the bootstrapped input stage, ensures that
the input current is essentially independent of the common-
mode voltage.
The AD549 is suited for applications requiring very low input
current and low input offset voltage. It excels as a preamp for a
wide variety of current output transducers, such as photodiodes,
photomultiplier tubes, or oxygen sensors. The AD549 can also
be used as a precision integrator or low droop sample-and-hold.
The AD549 is pin compatible with standard FET and electrometer
op amps, allowing designers to upgrade the performance of
present systems at little additional cost.
The AD549 is available in a TO-99 hermetic package. The case
is connected to Pin 8, thus, the metal case can be independently
Rev. H
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.
60 fA maximum (AD549L)
250 fA maximum (AD549J)
voltage range
0.25 mV maximum (AD549K)
1.00 mV maximum (AD549J)
5 μV/°C maximum (AD549K)
20 μV/°C maximum (AD549J)
700 μA maximum supply current
Low input voltage noise
15
Ω common-mode impedance,
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781.329.4700
Fax: 781.461.3113
connected to a point at the same potential as the input terminals,
minimizing stray leakage to the case. The AD549 is available in
four performance grades. The J, K, and L versions are rated over
the commercial temperature range of 0°C to +70°C. The S grade
is specified over the military temperature range of −55°C to +125°C
and is available processed to MIL-STD-883B, Rev. C. Extended
reliability plus screening is also available. Plus screening includes
168 hour burn-in, as well as other environmental and physical
tests derived from MIL-STD-883B, Rev. C.
PRODUCT HIGHLIGHTS
1.
2.
3.
4.
The AD549 input currents are specified, 100% tested, and
guaranteed after the device is warmed up. They are guaran-
teed over the entire common-mode input voltage range.
The AD549 input offset voltage and drift are laser trimmed
to 0.25 mV and 5 μV/°C (AD549K), and to 1 mV and
20 μV/°C (AD549J).
A maximum quiescent supply current of 700 μA minimizes
heating effects on input current and offset voltage.
AC specifications include 1 MHz unity-gain bandwidth
and 3 V/μs slew rate. Settling time for a 10 V input step is
5 μs to 0.01%.
Ultralow Input Bias Current
NONINVERTING
INVERTING
OFFSET NULL
CONNECTION DIAGRAM
©2002–2008 Analog Devices, Inc. All rights reserved.
Operational Amplifier
INPUT
INPUT
2
1
1
3
CONNECTED
Figure 1.
GUARD PIN,
TO CASE
AD549
V
OS
10kΩ
8
V–
4
TRIM
7
5
V+
OFFSET
NULL
5
4
6
–15V
OUTPUT
www.analog.com
AD549

AD549 Summary of contents

Page 1

... They are guaran- teed over the entire common-mode input voltage range. 2. The AD549 input offset voltage and drift are laser trimmed to 0.25 mV and 5 μV/°C (AD549K), and and 20 μV/°C (AD549J maximum quiescent supply current of 700 μA minimizes heating effects on input current and offset voltage ...

Page 2

... AD549 TABLE OF CONTENTS Features .............................................................................................. 1 Applications ....................................................................................... 1 Connection Diagram ....................................................................... 1 General Description ......................................................................... 1 Product Highlights ........................................................................... 1 Revision History ............................................................................... 2 Specifications ..................................................................................... 3 Absolute Maximum Ratings ............................................................ 5 ESD Caution .................................................................................. 5 Typical Performance Characteristics ............................................. 6 Functional Description .................................................................. 10 Minimizing Input Current ........................................................ 10 Circuit Board Notes ................................................................... 10 REVISION HISTORY 3/08—Rev Rev. H Changes to Features .......................................................................... 1 Changes to Figure 1 .......................................................................... 1 Deleted Package Option Parameter ............................................... 4 Inserted ESD Caution ...

Page 3

... AD549 Unit μV/°C μV/V μV/V μV/month μV p-p nV/√Hz nV/√Hz nV/√Hz nV/√Hz fA rms fA/√Hz Ω||pF Ω||pF V/mV V/mV V/mV V/ ...

Page 4

... Bias current increases by a factor of 2.3 for every 10°C rise in temperature 25°C. A Rev Page AD549L AD549S Max Min Typ Max +12 −12 +12 +10 −10 + 4000 4000 1.0 0.7 1.0 ...

Page 5

... Input Voltage Output Short-Circuit Duration Differential Input Voltage Storage Temperature Range Operating Temperature Range AD549J, AD549K, AD549L AD549S Lead Temperature (Soldering, 60 sec) 1 For supply voltages less than ±18 V, the absolute maximum input voltage is equal to the supply voltage. Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device ...

Page 6

... AD549 TYPICAL PERFORMANCE CHARACTERISTICS IN SUPPLY VOLTAGE (±V) Figure 2. Input Voltage Range vs. Supply Voltage 20 25° 10kΩ SUPPLY VOLTAGE (±V) Figure 3. Output Voltage Swing vs. Supply Voltage 100 1k LOAD RESISTANCE (Ω) Figure 4 ...

Page 7

... Figure 12. Input Voltage Noise Spectral Density WHENEVER JOHNSON NOISE IS GREATER THAN AMPLIFIER NOISE, AMPLIFIER NOISE CAN BE CONSIDERED NEGLIGIBLE FOR THE APPLICATION 1kHz BANDWIDTH RESISTOR JOHNSON NOISE 10Hz BANDWIDTH AMPLIFIER GENERATED NOISE 1M 10M 100M 1G 10G SOURCE RESISTANCE (Ω) Figure 13. Noise vs. Source Resistance AD549 20 10k 100G ...

Page 8

... AD549 100 –20 –40 10 100 1k 10k 100k FREQUENCY (Hz) Figure 14. Open-Loop Frequency Response 100 1k 10k FREQUENCY (Hz) Figure 15. Large Signal Frequency Response 100 –20 10 100 1k 10k FREQUENCY (Hz) Figure 16. CMRR vs. Frequency 100 –20 – ...

Page 9

... WAVE INPUT 5V Figure 23. Unity-Gain Inverter Large Signal Pulse Response 10mV Figure 24. Unity-Gain Inverter Small Signal Pulse Response Rev Page AD549 10kΩ 0.1µF 10kΩ AD549 V 5 OUT 10kΩ 100pF 4 3 0.1µF –V S Figure 22. Unity-Gain Inverter 5µ ...

Page 10

... Keep the amplifier operating temperature as low as possible to minimize input current. Like other JFET input amplifiers, the AD549 input current is sensitive to chip temperature, rising by a factor of 2.3 for every 10°C. Figure plot of the AD549 input current vs. ambient temperature. 1nA 100pA ...

Page 11

... The case of the AD549 is connected to Pin 8 so that it can be bootstrapped near the input potential. This minimizes pin leakage and input common-mode capacitance due to the case. Guard schemes for inverting and noninverting amplifier topologies are illustrated in Figure 28 and Figure 29. C GUARD R 2 AD549 ...

Page 12

... FEEDBACK RESISTANCE Source and feedback resistances greater than 100 kΩ magnify the effect of the input capacitances (stray and inherent to the AD549) on the ac behavior of the circuit. The effects of common-mode and differential input capacitances should be taken into account because the circuit bandwidth and stability can be adversely affected ...

Page 13

... Again, the Johnson noise voltage noise of the amplifier. Figure schematic of the AD549 as an inverter with an input voltage clamp. Bootstrapping the clamp diodes at the inverting input minimizes the voltage across the clamps and I ...

Page 14

... R2 PHOTODIODE INTERFACE 9.01kΩ R1 The low input current and low input offset voltage of the AD549 1kΩ make it an excellent choice for very sensitive photodiode preamps (see Figure 41). The photodiode develops a signal current, I CAL/TEST + equal to ...

Page 15

... LOG RATIO AMPLIFIER Logarithmic ratio circuits are useful for processing signals with wide dynamic range. The 60 fA maximum input current of the AD549L makes it possible to build a log ratio amplifier with 1% log conformance for input currents ranging from mA, a dynamic range of 160 dB. ...

Page 16

... The circuit in Figure 46 illustrates the use of the AD549 probe amplifier. As with other electrometer applications, the use of guarding, shielding, and Teflon standoffs is necessary to capitalize on the AD549 low input current ...

Page 17

... The AD549 is set for a noninverting gain of 13.51. The output of the AD590 circuitry (Point C) is equal 100°C and decreases by 26.8 mV/°C. The output of the AD590 tempera- AD534 analog divider (Point temperature-compensated output voltage centered for and has a transfer function of – ...

Page 18

... Model Temperature Range AD549JH 0°C to +70°C 1 AD549JHZ 0°C to +70°C AD549KH 0°C to +70°C 1 AD549KHZ 0°C to +70°C AD549LH 0°C to +70°C 1 AD549LHZ 0°C to +70°C AD549SH/883B −55°C to +125° RoHS Compliant Part. REFERENCE PLANE 0.5000 (12.70) MIN 0.1000 (2.54) ...

Page 19

... NOTES Rev Page AD549 ...

Page 20

... AD549 NOTES ©2002–2008 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. D00511-0-3/08(H) Rev Page ...

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