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AD549JH-AD549LH
Ultralow Input Bias Current Operational Amplifier
CONNECTION DIAGRAM
AD549
OFFSET NULL
OUTPUT
OFFSET
NULLNONINVERTING
INPUT1V+
GUARD PIN, CONNECTED TO CASE
INVERTING
INPUT
VOS TRIM
–15V
10kΩ
NC = NO CONNECTIONREV.A
Ultralow Input Bias Current
Operational Amplifier
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 mV/8C max (AD549K)
20 mV/8C max (AD549J)
Low Power: 700 mA max Supply Current
Low Input Voltage Noise: 4 mV p-p 0.1 Hz to 10 Hz
MIL-STD-883B Parts Available
APPLICATIONS
Electrometer Amplifiers
Photodiode Preamp
pH Electrode Buffer
Vacuum lon Gage Measurement
PRODUCT DESCRIPTIONThe 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.
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.
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.
*Protected by Patent No. 4,639,683.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.
PRODUCT HIGHLIGHTSThe 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’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).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%.The AD549 is an improved replacement for the AD515,
OPA104, and 3528.
AD549–SPECIFICATIONSINPUT BIAS CURRENT
INPUT OFFSET VOLTAGE
INPUT VOLTAGE NOISE
INPUT IMPEDANCE
OPEN-LOOP GAIN
FREQUENCY RESPONSE
(@ +258C and VS = +15 V dc, unless otherwise noted)
NOTESBias current specifications are guaranteed after 5 minutes of operation at TA = +25°C. Bias current increases by a factor of 2.3 for every 10°C rise in temperature.Input offset voltage specifications are guaranteed after 5 minutes of operation at TA = +25°C.Defined as max continuous voltage between the inputs such that neither input exceeds ±10 V from ground.
Specifications subject to change without notice.
All min and max specifications are guaranteed. Specifications in boldface are tested on all production units at final electrical test. Results from those tests are used to
calculate outgoing quality levels.
METALIZATION PHOTOGRAPHDimensions shown in inches and (mm).
Contact factory for latest dimensions.
ABSOLUTE MAXIMUM RATINGS1SupplyVoltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .±18V
InternalPowerDissipation . . . . . . . . . . . . . . . . . . . . . .500 mW
Input Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .±18 V2
Output Short Circuit Duration . . . . . . . . . . . . . . . . .Indefinite
DifferentialInputVoltage . . . . . . . . . . . . . . . . . .+VS and –VS
Storage Temperature Range (H) . . . . . . . . . .–65°C to +125°C
Operating Temperature Range
AD549J (K, L) . . . . . . . . . . . . . . . . . . . . . . . .0°C to +70°C
AD549S . . . . . . . . . . . . . . . . . . . . . . . . . .–55°C to +125°C
Lead Temperature Range (Soldering60sec) . . . . . . . .+300°C
NOTESStresses above those listed under “Absolute Maximum Ratings” may cause
permanent damage to the device. This is a stress rating only and 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.For supply voltages less than ±18 V, the absolute maximum input voltage is equal
to the supply voltage.
AD549
CAUTIONESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000V readily
accumulate on the human body and test equipment and can discharge without detection.
Although the AD549 features proprietary ESD protection circuitry, permanent damage may
occur on devices subjected to high energy electrostatic discharges. Therefore, proper ESD
precautions are recommended to avoid performance degradation or loss of functionality.
AD549–Typical Characteristics
SUPPLY VOLTAGE ± V
INPUT VOLTAGE 0 5 10 15 20Figure 1.Input Voltage Range
vs. Supply Voltage
SUPPLY VOLTAGE ± V
AMPLIFIER QUIESCENT CURRENT – µA
0 5 10 15 20Figure 4.Quiescent Current
vs. Supply Voltage
TEMPERATURE – °C
OPEN-LOOP GAIN – V/mV
–55 –25 5 35 65 95 125
100Figure 7.Open-Loop Gain vs.
Temperature
SUPPLY VOLTAGE ± V
OUTPUT VOLTAGE SWING
0 5 10 15 20Figure 2.Output Voltage
Swing vs. Supply Voltage
INPUT COMMON-MODE VOLTAGE – V
COMMON-MODE REJECTION RATIO – dB
–15 –10 0 +10 +15
110Figure 5.CMRR vs. Input
Common-Mode Voltage
WARM-UP TIME – Minutes
| – µV
0 1 2 3 4 5 6 7Figure 8.Change in Offset
Voltage vs. Warm-Up Time
Figure 3.Output Voltage
Swing vs. Load Resistance
SUPPLY VOLTAGE ± V
OPEN-LOOP GAIN – V/mV
0 5 10 15 20
100Figure 6.Open-Loop Gain vs.
Supply Voltage
COMMON-MODE VOLTAGE ± V
INPUT CURRENT – fA
–10 –5 0 5 10Figure 9.Input Bias Current
vs. Common-Mode Voltage
POWER SUPPLY VOLTAGE ± V
INPUT CURRENT – fA
0 5 10 15 20Figure 10.Input Bias Current
vs. Supply Voltage
FREQUENCY – Hz
OPEN LOOP GAIN – dB
10 100 1k 10k 100k 1M 10M
PHASE MARGIN – Figure 13.Open-Loop
Frequency Response
FREQUENCY – Hz
10 100 1k 10k
NOISE SPECTRAL DENSITY – nV/Figure 11.Input Voltage Noise
Spectral Density
OUTPUT VOLTAGE SWING – V
FREQUENCY – Hz
10 100 1k 10k 100k 1MFigure 14.Large Signal
Frequency Response
Figure 12.Noise vs. Source
Resistance
Figure 15.CMRR vs. Frequency
FREQUENCY – Hz
PSRR – dB
10 100 1k 10k 100k 1M 10MFigure 16.PSRR vs. Frequency
Figure 17.Output Voltage
Swing and Error vs.
AD549 Figure 18.Unity Gain
Follower
Figure 21.Unity Gain Inverter
Figure 19.Unity Gain Follower
Large Signal Pulse Response
Figure 22.Unity Gain Inverter
Large Signal Pulse Response
Figure 20.Unity Gain Follower
Small Signal Pulse Response
Figure 23.Unity Gain Inverter
Small Signal Pulse Response
MINIMIZING INPUT CURRENTThe AD549 has been optimized for low input current and offset
voltage. Careful attention to how the amplifier is used will reduce
input currents in actual applications.
The amplifier operating temperature should be kept as low as pos-
sible to minimize input current. Like other JFET input amplifiers,
the AD549’s input current is sensitive to chip temperature, rising
by a factor of 2.3 for every 10°C rise. This is illustrated in Figure
24, a plot of AD549 input current versus ambient temperature.
TEMPERATURE – °C
1nA
100pA
10pA
1fA
–55 –25 5 35 65 95 125
1pA
100fA
10fAFigure 24.AD549 Input Bias Current vs.
Ambient Temperature
On-chip power dissipation will raise chip operating temperature
causing an increase in input bias current. Due to the AD549’s
However, heavy output loads can cause a significant increase
in chip temperature and a corresponding increase in input
current. Maintaining a minimum load resistance of 10 Ω is rec-
ommended. Input current versus additional power dissipation
due to output drive current is plotted in Figure 25.
Figure 25.AD549 Input Bias Current vs.
Additional Power Dissipation
CIRCUIT BOARD NOTESThere are a number of physical phenomena that generate
spurious currents that degrade the accuracy of low current
measurements. Figure 26 is a schematic of an I-to-V converter
with these parasitic currents modeled.
Finite resistance from input lines to voltages on the board,
