AD549_08 Datasheet, PDF (1/20 Pages) Analog Devices – Ultralow Input Bias Current Operational Amplifier

FEATURES
Ultralow input bias current
60 fA maximum (AD549L)
250 fA maximum (AD549J)
Input bias current guaranteed over the common-mode
voltage range
Low offset voltage
0.25 mV maximum (AD549K)
1.00 mV maximum (AD549J)
Low offset drift
5 μV/°C maximum (AD549K)
20 μV/°C maximum (AD549J)
Low power
700 μA maximum supply current
Low input voltage noise
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 AD549¹ 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 10¹⁵ Ω common-mode impedance,
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
1 _{Protected by U.S. Patent No. 4,639,683.}
Rev. H
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Ultralow Input Bias Current
Operational Amplifier
AD549
CONNECTION DIAGRAM
GUARD PIN,
CONNECTED
TO CASE
OFFSET NULL
8
V+
1 _{AD549 7}
INVERTING
INPUT
2
6 OUTPUT
3
NONINVERTING
INPUT
5
OFFSET
4
NULL
V–
10kΩ
1
5
V_OS TRIM
4 –15V
Figure 1.
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. 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.
2. 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).
3. A maximum quiescent supply current of 700 μA minimizes
heating effects on input current and offset voltage.
4. 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%.
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