Ultralow Input Bias Current
Operational Amplifier
a
AD549*
CONNECTION DIAGRAM
FEATURES
Ultralow Bias Current: 60 fA max (AD549L)
250 fA max (AD549J)
Input Bias Current Guaranteed Over Common-Mode
Voltage Range
Low Offset Voltage: 0.25 mV max (AD549K)
1.00 mV max (AD549J)
Low Offset Drift: 5 V/؇C max (AD549K)
20 V/؇C max (AD549J)
GUARD PIN, CONNECTED TO CASE
NC
OFFSET NULL
8
V+
1
7
5
AD549
INVERTING
2
6
OUTPUT
INPUT
3
Low Power: 700 A max Supply Current
Low Input Voltage Noise: 4 V p-p 0.1 Hz to 10 Hz
MIL-STD-883B Parts Available
OFFSET
NULL
4
NONINVERTING
INPUT
V–
10kΩ
APPLICATIONS
5
1
Electrometer Amplifiers
Photodiode Preamp
pH Electrode Buffer
–15V
4
V
TRIM
OS
NC = NO CONNECTION
Vacuum lon Gage Measurement
PRODUCT DESCRIPTION
The AD549 is available in four performance grades. The J, K,
and L versions are rated over the commercial temperature range
0°C to +70°C. The S grade is specified over the military tem-
perature 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.
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 AD549’s ultralow input current is achieved with “Topgate”
JFET technology, a process development exclusive to Analog
Devices. This technology allows the fabrication of extremely low
input current JFETs compatible with a standard junction-
isolated bipolar process. The 1015 Ω common-mode impedance,
a result of the bootstrapped input stage, insures that the input
current is essentially independent of common-mode voltage.
PRODUCT HIGHLIGHTS
1. The AD549’s input currents are specified, 100% tested and
guaranteed after the device is warmed up. Input current is
guaranteed over the entire common-mode input voltage
range.
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 electrom-
eter op amps, allowing designers to upgrade the performance of
present systems at little additional cost.
2. The AD549’s input offset voltage and drift are laser trimmed
to 0.25 mV and 5 µV/°C (AD549K), 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.
The AD549 is available in a TO-99 hermetic package. The case
is connected to Pin 8 so that the metal case can be independently
connected to a point at the same potential as the input termi-
nals, minimizing stray leakage to the case.
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%.
5. The AD549 is an improved replacement for the AD515,
OPA104, and 3528.
*Protected by Patent No. 4,639,683.
REV. A
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
which may result from its use. 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: 617/329-4700
Fax: 617/326-8703
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