ad795.pdf

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a
Low Power, Low Noise
Precision FET Op Amp
AD795
FEATURES
Low Power Replacement for Burr-Brown
OPA-111, OPA-121 Op Amps
Low Noise
2.5 m V p-p max, 0.1 Hz to 10 Hz
11 nV/ Ö Hz max at 10 kHz
0.6 fA/ Ö Hz at 1 kHz
High DC Accuracy
250 m V max Offset Voltage
3 m V/ 8 C max Drift
1 pA max Input Bias Current
Low Power: 1.5 mA max Supply Current
Available in Low Cost Plastic Mini-DIP and Surface
Mount (SOIC) Packages
CONNECTION DIAGRAMS
8-Pin Plastic Mini-DIP (N) Package
30
V s = ±15V
25
20
15
10
5
0
10
100
1k
10k
LOAD RESISTANCE –
W
8-Pin SOIC (R) Package
NC
–IN
+IN
–V S
1
2
3
4
8
7
6
5
NC
+V S
OUTPUT
NC
APPLICATIONS
Low Noise Photodiode Preamps
CT Scanners
Precision l-to-V Converters
AD795
NC = NO CONNECT
PRODUCT DESCRIPTION
The AD795 is a low noise, precision, FET input operational
amplifier. It offers both the low voltage noise and low offset drift
of a bipolar input op amp and the very low bias current of a
FET-input device. The 10 14 W common-mode impedance
insures that input bias current is essentially independent of
common-mode voltage and supply voltage variations.
The AD795 has both excellent dc performance and a guaran-
teed and tested maximum input voltage noise. It features 1 pA
maximum input bias current and 250 mV maximum offset volt-
age, along with low supply current of 1.5 mA max.
Hz max noise
level at 10 kHz. The AD795 has a fully specified and tested
input offset voltage drift of only 3
V p-p (0.1 Hz to 10 Hz) and a 11 nV/
Ö
C max.
The AD795 is useful for many high input impedance, low noise
applications. The AD795J and AD795K are rated over the
commercial temperature range of 0
m
V/
°
C.
The AD795 is available in 8-pin plastic mini-DIP and 8-pin
surface mount (SOIC) packages.
°
C to +70
°
1k
50
SAMPLE SIZE = 570
40
100
30
10
20
10
1
0
10
100
1k
10k
–5
–4
–3
INPUT OFFSET VOLTAGE DRIFT – m V/ ° C
–2
–1
0
1
2
3
4
5
FREQUENCY – Hz
AD795 Voltage Noise Spectral Density
Typical Distribution of Average Input Offset Voltage Drift
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
Furthermore, the AD795 features a guaranteed low input noise
of 2.5
m
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AD795–SPECIFICATIONS
(@ +25
8
C and
6
15 V dc unless otherwise noted)
AD795JN/JR
AD795K
Parameter
Conditions
Min
Typ
Max
Min
Typ
Max
Units
INPUT OFFSET VOLTAGE 1
Initial Offset
100
500
50
250
mV
Offset
T MIN –T MAX
300
1000
100
400
mV
vs. Temperature
3
10
1
3
mV/°C
vs. Supply (PSRR)
86
110
90
110
dB
vs. Supply (PSRR)
T MIN –T MAX
84
100
87
100
dB
INPUT BIAS CURRENT 2
Either Input
V CM = 0 V
1
2/3
1
1
pA
Either Input @ T MAX =
V CM = 0 V
23
23
pA
Either Input
V CM = +10 V
1
1
pA
Offset Current
V CM = 0 V
0.1
1.0
0.1
0.6
pA
Offset Current @ T MAX =
V CM = 0 V
2
2
pA
OPEN-LOOP GAIN
V O = ± 10 V
R LOAD ³ 10 kW
110
120
110
120
dB
R LOAD ³ 10 kW
100
108
100
108
dB
INPUT VOLTAGE NOISE
0.1 Hz to 10 Hz
1.0
3.3
1.0
2.5
mV p-p
f = 10 Hz
20
50
20
40
nV/ÖHz
f = 100 Hz
12
40
12
30
nV/ÖHz
f = 1 kHz
11
17
11
15
nV/ÖHz
f = 10 kHz
9
11
9
11
nV/ÖHz
INPUT CURRENT NOISE
f = 0.1 Hz to 10 Hz
13
13
fA p-p
f = 1 kHz
0.6
0.6
fA/ÖHz
FREQUENCY RESPONSE
Unity Gain, Small Signal
G = –1
1.6
1.6
MHz
Full Power Response
V O = 20 V p-p
R LOAD = 2 kW
16
16
kHz
Slow Rate, Unity Gain
V OUT = 20 V p-p
R LOAD = 2 kW
1
1
V/ms
SETTLING TIME 3
To 0.1%
10 V Step
10
10
ms
To 0.01%
10 V Step
11
11
ms
Overload Recovery 4
50% Overdrive
2
2
ms
Total Harmonic
f = 1 kHz
Distortion
R1 ³ 10 kW
V O = 3 V rms
–108
–108
dB
INPUT IMPEDANCE
Differential
V DIFF = ± 1 V
10 12
i 2
10 12
i 2
W i pF
Common Mode
10 14
i 2.2
10 14
i 2.2
W i pF
INPUT VOLTAGE RANGE
Differential 5
± 20
± 20
V
Common-Mode Voltage
± 10
± 11
± 10
± 11
V
Over Max Operating Temperature
± 10
± 10
V
Common-Mode Rejection Ratio
V CM = ± 10 V
90
110
94
110
dB
T MIN –T MAX
86
100
90
100
dB
OUTPUT CHARACTERISTICS
Voltage
R LOAD ³ 2 kW
V S –4
V S –2.5
V S –4 V S –2.5
V
T MIN –T MAX
V S –4
V S –4
V
Current
V OUT = ± 10 V
± 5
± 10
± 5
± 10
mA
Short Circuit
± 15
± 15
mA
POWER SUPPLY
Rated Performance
± 15
± 15
V
Operating Range
± 4
± 18
± 4
± 18
V
Quiescent Current
1.3
1.5
1.3
1.5
mA
–2–
REV. A
11023700.007.png 11023700.008.png
AD795
C.
2 Bias current specifications are guaranteed maximum at either input after 5 minutes of operation at T A = +25
°
°
C. For higher temperature, the current doubles every 10
°
C.
.
4 Defined as the time required for the amplifier’s output to return to normal operation after removal of a 50% overload from the amplifier input.
5 Defined as the maximum continuous voltage between the inputs such that neither input exceeds
W
±
10 V from ground.
All min and max specifications are guaranteed.
Specifications subject to change without notice.
ABSOLUTE MAXIMUM RATINGS 1
Supply Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ± 18 V
Internal Power Dissipation 2 (@ T A = +25°C)
SOIC Package . . . . . . . . . . . . . . . . . . . . . . . . . . . . 500 mW
8-Pin Mini-DIP Package . . . . . . . . . . . . . . . . . . . . 750 mW
Input Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ± V S
Output Short Circuit Duration . . . . . . . . . . . . . . . . Indefinite
Differential Input Voltage . . . . . . . . . . . . . . . . . . +V S and –V S
Storage Temperature Range (N, R) . . . . . . . –65°C to +125°C
Operating Temperature Range
AD795J/K . . . . . . . . . . . . . . . . . . . . . . . . . . . 0°C to +70°C
NOTES
1 Stresses 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.
2 8-Pin Plastic Mini-DIP Package:
ESD SUSCEPTIBILITY
ESD (electrostatic discharge) sensitive device. Electrostatic
charges as high as 4000 volts, which readily accumulate on the
human body and on test equipment, can discharge without
detection. Although the AD795 features proprietary ESD pro-
tection circuitry, permanent damage may still occur on these
devices if they are subjected to high energy electrostatic dis-
charges. Therefore, proper ESD precautions are recommended
to avoid any performance degradation or loss of functionality.
ORDERING GUIDE
Model
Temperature Range
Package Option*
AD795JN
0
°
C to +70
°
C
N-8
AD795KN
0
°
C to +70
°
C
N-8
q JA = 100
°
C/Watt
AD795JR
0
°
C to +70
°
C
R-8
8-Pin Small Outline Package:
q JA = 155
°
C/Watt
*N = Plastic mini-DIP; R = SOIC package.
REV. A
–3–
NOTES
1 Input offset voltage specifications are guaranteed after 5 minutes of operation at T A = +25
3 Gain = –1, R1 = 10 k
11023700.009.png
AD795–Typical Characteristics
20
20
R L = 10k
W
R L = 10k
W
15
+V IN
15
+V OUT
10
10
–V IN
–V OUT
5
5
0
0
0
5
10
15
20
0
5
10
15
20
SUPPLY VOLTAGE – ±Volts
SUPPLY VOLTAGE – ±Volts
Figure 1. Common-Mode Voltage Range vs. Supply
Figure 2. Output Voltage Range vs. Supply Voltage
30
1.0
V s = ±15V
0.95
25
0.90
20
0.85
15
0.80
10
0.75
0.70
5
0.65
0
0.60
0
5
10
SUPPLY VOLTAGE – ±Volts
15
20
10
100
1k
10k
W
Figure 3. Output Voltage Swing vs. Load Resistance
LOAD RESISTANCE –
Figure 4. Input Bias Current vs. Supply
50
10 –9
SAMPLE SIZE = 1058
10 –10
40
30
10 –11
20
10 –12
10
10 –13
0
10 –14
0
.5
1
1.5
2
–60
–40
–20
0
20
40
60
80
100
120
140
TEMPERATURE – ° C
INPUT BIAS CURRENT – pA
Figure 5. Typical Distribution of Input Bias Current
Figure 6. Input Bias Current vs. Temperature
–4–
REV. A
11023700.010.png
AD795
1.00
10 –4
0.95
10 –5
10 –6
10 –7
–I IN
+I IN
0.90
0.85
10 –8
0.80
10 –9
10 –10
0.75
10 –11
0.70
10 –12
0.65
10 –13
10 –14
0.60
–6 –5 –4 –3 –2
–1
0
12
3
4
56
0
–15
–10
–5
+5
+10
+15
DIFFERENTIAL INPUT VOLTAGE – ±Volts
COMMON MODE VOLTAGE – Volts
Figure 7. Input Bias Current vs. Common-Mode Voltage
Figure 8. Input Bias Current vs. Differential Input Voltage
15
100
1k
f = 1kHz
Noise Bandwidth: 0.1 to 10Hz
12.5
VOLTAGE NOISE
10
100
10
1.0
CURRENT NOISE
10
7.5
0.1
5
0.01
1.0
–60
–40
–20
0
20
40
60
80
100 120
140
10 3
10 4
10 5
10 6
10 7
10 8
10 9
TEMPERATURE – ° C
SOURCE RESISTANCE –
W
Figure 9. Voltage and Current Noise Spectral Density vs.
Temperature
Figure 10. Input Voltage Noise vs. Source Resistance
1k
50
SAMPLE SIZE = 344
40
f = 0.1 TO 10Hz
100
30
20
10
10
1.0
0
1
10
100
1k
10k
100k
1M
10M
0
1
2
3
FREQUENCY – Hz
0.1 TO 10Hz INPUT VOLTAGE NOISE p-p –
m
V
Figure 11. Typical Distribution of Input Voltage Noise
Figure 12. Input Voltage Noise Spectral Density
REV. A
–5–
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