NSC LMC6081IM Precision cmos single operational amplifier Datasheet

LMC6081
Precision CMOS Single Operational Amplifier
General Description
Features
The LMC6081 is a precision low offset voltage operational
amplifier, capable of single supply operation. Performance
characteristics include ultra low input bias current, high voltage gain, rail-to-rail output swing, and an input common
mode voltage range that includes ground. These features,
plus its low offset voltage, make the LMC6081 ideally suited
for precision circuit applications.
Other applications using the LMC6081 include precision
full-wave
rectifiers,
integrators,
references,
and
sample-and-hold circuits.
This device is built with National’s advanced Double-Poly
Silicon-Gate CMOS process.
For designs with more critical power demands, see the
LMC6061 precision micropower operational amplifier.
For a dual or quad operational amplifier with similar features,
see the LMC6082 or LMC6084 respectively.
PATENT PENDING
(Typical unless otherwise stated)
n Low offset voltage: 150 µV
n Operates from 4.5V to 15V single supply
n Ultra low input bias current: 10 fA
n Output swing to within 20 mV of supply rail, 100k load
n Input common-mode range includes V−
n High voltage gain: 130 dB
n Improved latchup immunity
Applications
n
n
n
n
n
n
Instrumentation amplifier
Photodiode and infrared detector preamplifier
Transducer amplifiers
Medical instrumentation
D/A converter
Charge amplifier for piezoelectric transducers
Connection Diagram
8-Pin DIP/SO
DS011423-1
Top View
Ordering Information
Package
Temperature Range
Military
8-Pin
Industrial
−55˚C to +125˚C
−40˚C to +85˚C
LMC6081AMN
LMC6081AIN
Molded DIP
Transport
Media
N08E
Rail
LMC6081IN
8-Pin
LMC6081AIM
Small Outline
LMC6081IM
© 1999 National Semiconductor Corporation
NSC
Drawing
DS011423
M08A
Rail
Tape and Reel
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LMC6081 Precision CMOS Single Operational Amplifier
November 1994
Absolute Maximum Ratings (Note 1)
± Supply Voltage
Differential Input Voltage
Voltage at Input/Output Pin
Supply Voltage (V+ − V−)
Output Short Circuit to V+
Output Short Circuit to V−
Lead Temperature
(Soldering, 10 Sec.)
Storage Temp. Range
Junction Temperature
ESD Tolerance (Note 4)
± 10 mA
± 30 mA
Current at Input Pin
Current at Output Pin
Current at Power Supply Pin
Power Dissipation
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
40 mA
(Note 3)
Operating Ratings (Note 1)
(V+) +0.3V,
(V−) −0.3V
16V
(Note 10)
(Note 2)
Temperature Range
LMC6081AM
LMC6081AI, LMC6081I
Supply Voltage
Thermal Resistance (θJA), (Note 11)
N Package, 8-Pin Molded DIP
M Package, 8-Pin Surface Mount
Power Dissipation (Note 9)
260˚C
−65˚C to +150˚C
150˚C
2 kV
−55˚C ≤ TJ ≤ +125˚C
−40˚C ≤ TJ ≤ +85˚C
4.5V ≤ V+ ≤ 15.5V
115˚C/W
193˚C/W
DC Electrical Characteristics
Unless otherwise specified, all limits guaranteed for TJ = 25˚C. Boldface limits apply at the temperature extremes. V+ = 5V, V−
= 0V, VCM = 1.5V, VO = 2.5V and RL > 1M unless otherwise specified.
Symbol
VOS
TCVOS
Parameter
Conditions
Input Offset Voltage
Typ
LMC6081AM
LMC6081AI
(Note 5)
Limit
Limit
Limit
(Note 6)
(Note 6)
(Note 6)
350
350
800
µV
1000
800
1300
Max
150
Input Offset Voltage
LMC6081I
1.0
Units
µV/˚C
Average Drift
IB
IOS
Input Bias Current
Input Offset Current
RIN
Input Resistance
CMRR
Common Mode
−PSRR
5V ≤ V+ ≤ 15V
VO = 2.5V
85
Rejection Ratio
Negative Power Supply
0V ≤ V− ≤ −10V
94
Rejection Ratio
VCM
Input Common-Mode
V+ = 5V and 15V
Voltage Range
for CMRR ≥ 60 dB
−0.4
V+ − 1.9
AV
Large Signal
RL = 2 kΩ
Voltage Gain
(Note 7)
RL = 600Ω
Sourcing
1400
4
Max
100
2
2
Max
75
75
66
dB
72
72
63
Min
75
75
66
dB
72
72
63
Min
pA
Tera Ω
84
84
74
dB
81
81
71
Min
−0.1
−0.1
−0.1
V
0
0
0
Max
V+ − 2.3
V+ − 2.3
V+ − 2.3
V
V+ − 2.6
V+ − 2.5
V+ − 2.5
Min
V/mV
400
400
300
300
300
200
Min
180
90
V/mV
Sinking
350
180
70
100
60
Min
Sourcing
1200
400
400
200
V/mV
150
150
80
Min
Sinking
150
100
100
70
V/mV
35
50
35
Min
(Note 7)
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4
> 10
85
Positive Power Supply
pA
100
0.005
0V ≤ VCM ≤ 12.0V
V+ = 15V
Rejection Ratio
+PSRR
0.010
2
DC Electrical Characteristics
(Continued)
Unless otherwise specified, all limits guaranteed for TJ = 25˚C. Boldface limits apply at the temperature extremes. V+ = 5V, V−
= 0V, VCM = 1.5V, VO = 2.5V and RL > 1M unless otherwise specified.
Symbol
VO
Parameter
Output Swing
Conditions
V+ = 5V
RL = 2 kΩ to 2.5V
Typ
LMC6081AM
LMC6081AI
(Note 5)
Limit
Limit
Limit
(Note 6)
(Note 6)
(Note 6)
4.80
4.80
4.75
V
4.70
4.73
4.67
Min
4.87
0.10
V+ = 5V
RL = 600Ω to 2.5V
4.61
0.30
V+ = 15V
RL = 2 kΩ to 7.5V
14.63
0.26
V+ = 15V
RL = 600Ω to 7.5V
13.90
0.79
IO
Output Current
V+ = 5V
Sourcing, VO = 0V
22
Sinking, VO = 5V
IO
Output Current
V+ = 15V
21
Sourcing, VO = 0V
30
Sinking, VO = 13V
IS
Supply Current
34
(Note 10)
V+ = +5V, VO = 1.5V
450
V+ = +15V, VO = 7.5V
550
3
LMC6081I
Units
0.13
0.13
0.20
V
0.19
0.17
0.24
Max
4.50
4.50
4.40
V
4.24
4.31
4.21
Min
0.40
0.40
0.50
V
0.63
0.50
0.63
Max
14.50
14.50
14.37
V
14.30
14.34
14.25
Min
0.35
0.35
0.44
V
0.48
0.45
0.56
Max
13.35
13.35
12.92
V
12.80
12.86
12.44
Min
1.16
1.16
1.33
V
1.42
1.32
1.58
Max
16
16
13
mA
8
10
8
Min
16
16
13
mA
11
13
10
Min
28
28
23
mA
18
22
18
Min
28
28
23
mA
19
22
18
Min
750
750
750
µA
900
900
900
Max
850
850
850
µA
950
950
950
Max
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AC Electrical Characteristics
Unless otherwise specified, all limits guaranteed for TJ = 25˚C, Boldface limits apply at the temperature extremes. V+ = 5V, V−
= 0V, VCM = 1.5V, VO = 2.5V and RL > 1M unless otherwise specified.
Symbol
SR
Parameter
Conditions
Slew Rate
(Note 8)
Typ
LMC6081AM
LMC6081AI
(Note 5)
Limit
Limit
Limit
(Note 6)
(Note 6)
(Note 6)
1.5
GBW
Gain-Bandwidth Product
φm
Phase Margin
en
Input-Referred
Voltage Noise
F = 1 kHz
22
in
Input-Referred
Current Noise
F = 1 kHz
0.0002
T.H.D.
Total Harmonic Distortion
F = 10 kHz, AV = −10
RL = 2 kΩ, VO = 8 VPP
LMC6081
0.8
0.8
0.8
0.5
0.6
0.6
Units
V/µs
Min
1.3
MHz
50
Deg
%
0.01
± 5V Supply
Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is intended to be functional, but do not guarantee specific performance limits. For guaranteed specifications and test conditions, see the Electrical Characteristics. The
guaranteed specifications apply only for the test conditions listed.
Note 2: Applies to both single-supply and split-supply operation. Continuous short circuit operation at elevated ambient temperature can result in exceeding the
maximum allowed junction temperature of 150˚C. Output currents in excess of ± 30 mA over long term may adversely affect reliability.
Note 3: The maximum power dissipation is a function of TJ(Max), θJA, and TA. The maximum allowable power dissipation at any ambient temperature is PD = (TJ(Max)
− TA) /θJA.
Note 4: Human body model, 1.5 kΩ in series with 100 pF.
Note 5: Typical values represent the most likely parametric norm.
Note 6: All limits are guaranteed by testing or statistical analysis.
Note 7: V+ = 15V, VCM = 7.5V and RL connected to 7.5V. For Sourcing tests, 7.5V ≤ VO ≤ 11.5V. For Sinking tests, 2.5V ≤ VO ≤ 7.5V.
Note 8: V+ = 15V. Connected as Voltage Follower with 10V step input. Number specified is the slower of the positive and negative slew rates.
Note 9: For operating at elevated temperatures the device must be derated based on the thermal resistance θJA with PD = (TJ − TA)/θJA.
Note 10: Do not connect output to V+, when V+ is greater than 13V or reliability will be adversely affected.
Note 11: All numbers apply for packages soldered directly into a PC board.
Typical Performance Characteristics
Distribution of LMC6081
Input Offset Voltage
(TA = +25˚C)
VS = ± 7.5V, TA = 25˚C, Unless otherwise specified
Distribution of LMC6081
Input Offset Voltage
(TA = −55˚C)
DS011423-15
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Distribution of LMC6081
Input Offset Voltage
(TA = +125˚C)
DS011423-16
4
DS011423-17
Typical Performance Characteristics
VS = ± 7.5V, TA = 25˚C, Unless otherwise
specified (Continued)
Input Bias Current
vs Temperature
Supply Current
vs Supply Voltage
DS011423-19
DS011423-18
Common Mode
Rejection Ratio
vs Frequency
Input Voltage
vs Output Voltage
Power Supply Rejection
Ratio vs Frequency
DS011423-20
Input Voltage Noise
vs Frequency
DS011423-22
DS011423-23
DS011423-21
Output Characteristics
Sourcing Current
Output Characteristics
Sinking Current
Gain and Phase Response
vs Temperature
(−55˚C to +125˚C)
DS011423-24
DS011423-25
5
DS011423-26
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Typical Performance Characteristics
VS = ± 7.5V, TA = 25˚C, Unless otherwise
specified (Continued)
Gain and Phase
Response vs Capacitive Load
with RL = 600Ω
Gain and Phase
Response vs Capacitive Load
with RL = 500 kΩ
Open Loop
Frequency Response
DS011423-29
DS011423-27
Inverting Small Signal
Pulse Response
DS011423-28
Inverting Large Signal
Pulse Response
DS011423-30
Non-Inverting Large
Signal Pulse Response
Non-Inverting Small
Signal Pulse Response
DS011423-31
Stability vs Capacitive
Load, RL = 600Ω
DS011423-33
DS011423-32
Stability vs Capacitive
Load RL = 1 MΩ
DS011423-34
DS011423-35
Applications Hints
micropower op-amps. These features make the LMC6081
both easier to design with, and provide higher speed than
products typically found in this ultra-low power class.
AMPLIFIER TOPOLOGY
The LMC6081 incorporates a novel op-amp design topology
that enables it to maintain rail-to-rail output swing even when
driving a large load. Instead of relying on a push-pull unity
gain output buffer stage, the output stage is taken directly
from the internal integrator, which provides both low output
impedance and large gain. Special feed-forward compensation design techniques are incorporated to maintain stability
over a wider range of operating conditions than traditional
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COMPENSATING FOR INPUT CAPACITANCE
It is quite common to use large values of feedback resistance for amplifiers with ultra-low input current, like the
LMC6081.
6
Applications Hints
(Continued)
Although the LMC6081 is highly stable over a wide range of
operating conditions, certain precautions must be met to
achieve the desired pulse response when a large feedback
resistor is used. Large feedback resistors and even small
values of input capacitance, due to transducers, photodiodes, and circuit board parasitics, reduce phase margins.
When high input impedances are demanded, guarding of the
LMC6081 is suggested. Guarding input lines will not only reduce leakage, but lowers stray input capacitance as well.
(See Printed-Circuit-Board Layout for High Impedance
Work).
The effect of input capacitance can be compensated for by
adding a capacitor, Cf, around the feedback resistors (as in
Figure 1 ) such that:
DS011423-5
FIGURE 2. LMC6081 Noninverting Gain of 10 Amplifier,
Compensated to Handle Capacitive Loads
or
R1 CIN ≤ R2 Cf
Since it is often difficult to know the exact value of CIN, Cf can
be experimentally adjusted so that the desired pulse response is achieved. Refer to the LMC660 and LMC662 for a
more detailed discussion on compensating for input
capacitance.
In the circuit of Figure 2, R1 and C1 serve to counteract the
loss of phase margin by feeding the high frequency component of the output signal back to the amplifier’s inverting input, thereby preserving phase margin in the overall feedback
loop.
Capacitive load driving capability is enhanced by using a pull
up resistor to V+ (Figure 3). Typically a pull up resistor conducting 500 µA or more will significantly improve capacitive
load responses. The value of the pull up resistor must be determined based on the current sinking capability of the amplifier with respect to the desired output swing. Open loop gain
of the amplifier can also be affected by the pull up resistor
(see electrical characteristics).
DS011423-4
FIGURE 1. Cancelling the Effect of Input Capacitance
CAPACITIVE LOAD TOLERANCE
All rail-to-rail output swing operational amplifiers have voltage gain in the output stage. A compensation capacitor is
normally included in this integrator stage. The frequency location of the dominant pole is affected by the resistive load
on the amplifier. Capacitive load driving capability can be optimized by using an appropriate resistive load in parallel with
the capacitive load (see typical curves).
Direct capacitive loading will reduce the phase margin of
many op-amps. A pole in the feedback loop is created by the
combination of the op-amp’s output impedance and the capacitive load. This pole induces phase lag at the unity-gain
crossover frequency of the amplifier resulting in either an oscillatory or underdamped pulse response. With a few external components, op amps can easily indirectly drive capacitive loads, as shown in Figure 2.
DS011423-14
FIGURE 3. Compensating for Large
Capacitive Loads with a Pull Up Resistor
PRINTED-CIRCUIT-BOARD LAYOUT
FOR HIGH-IMPEDANCE WORK
It is generally recognized that any circuit which must operate
with less than 1000 pA of leakage current requires special
layout of the PC board. When one wishes to take advantage
of the ultra-low bias current of the LMC6081, typically less
than 10 fA, it is essential to have an excellent layout. Fortunately, the techniques of obtaining low leakages are quite
simple. First, the user must not ignore the surface leakage of
the PC board, even though it may sometimes appear acceptably low, because under conditions of high humidity or dust
or contamination, the surface leakage will be appreciable.
To minimize the effect of any surface leakage, lay out a ring
of foil completely surrounding the LMC6081’s inputs and the
terminals of capacitors, diodes, conductors, resistors, relay
terminals, etc. connected to the op-amp’s inputs, as in Fig7
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Applications Hints
(Continued)
ure 4. To have a significant effect, guard rings should be
placed on both the top and bottom of the PC board. This PC
foil must then be connected to a voltage which is at the same
voltage as the amplifier inputs, since no leakage current can
flow between two points at the same potential. For example,
a PC board trace-to-pad resistance of 1012Ω, which is normally considered a very large resistance, could leak 5 pA if
the trace were a 5V bus adjacent to the pad of the input. This
would cause a 100 times degradation from the LMC6081’s
actual performance. However, if a guard ring is held within
5 mV of the inputs, then even a resistance of 1011Ω would
cause only 0.05 pA of leakage current. See Figure 5 for typical connections of guard rings for standard op-amp
configurations.
DS011423-7
Inverting Amplifier
DS011423-8
Non-Inverting Amplifier
DS011423-6
FIGURE 4. Example of Guard Ring in P.C. Board
Layout
DS011423-9
Follower
FIGURE 5. Typical Connections of Guard Rings
The designer should be aware that when it is inappropriate
to lay out a PC board for the sake of just a few circuits, there
is another technique which is even better than a guard ring
on a PC board: Don’t insert the amplifier’s input pin into the
board at all, but bend it up in the air and use only air as an insulator. Air is an excellent insulator. In this case you may
have to forego some of the advantages of PC board construction, but the advantages are sometimes well worth the
effort of using point-to-point up-in-the-air wiring.
See Figure 6.
DS011423-10
(Input pins are lifted out of PC board and soldered directly to components.
All other pins connected to PC board).
FIGURE 6. Air Wiring
Latchup
CMOS devices tend to be susceptible to latchup due to their
internal parasitic SCR effects. The (I/O) input and output pins
look similar to the gate of the SCR. There is a minimum curwww.national.com
8
Latchup
require battery-powered instrumentation amplifiers. Examples of these types of applications are hand-held pH
probes, analytic medical instruments, magnetic field detectors, gas detectors, and silicon based pressure transducers.
(Continued)
rent required to trigger the SCR gate lead. The LMC6061
and LMC6081 are designed to withstand 100 mA surge current on the I/O pins. Some resistive method should be used
to isolate any capacitance from supplying excess current to
the I/O pins. In addition, like an SCR, there is a minimum
holding current for any latchup mode. Limiting current to the
supply pins will also inhibit latchup susceptibility.
Figure 7 shows an instrumentation amplifier that features
high differential and common mode input resistance
( > 1014Ω), 0.01% gain accuracy at AV = 1000, excellent
CMRR with 1 kΩ imbalance in bridge source resistance. Input current is less than 100 fA and offset drift is less than
2.5 µV/˚C. R2 provides a simple means of adjusting gain
over a wide range without degrading CMRR. R7 is an initial
trim used to maximize CMRR without using super precision
matched resistors. For good CMRR over temperature, low
drift resistors should be used.
Typical Single-Supply
Applications
(V+ = 5.0 VDC)
The extremely high input impedance, and low power consumption, of the LMC6081 make it ideal for applications that
DS011423-11
If R1 = R5, R3 = R6, and R4 = R7; then
AV ≈ 100 for circuit shown (R2 = 9.822k).
FIGURE 7. Instrumentation Amplifier
DS011423-12
FIGURE 8. Low-Leakage Sample and Hold
9
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Typical Single-Supply
Applications (Continued)
DS011423-13
FIGURE 9. 1 Hz Square Wave Oscillator
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10
Physical Dimensions
inches (millimeters) unless otherwise noted
8-Pin Small Outline Package
Order Number LMC6081AIM or LMC6081IM
NS Package Number M08A
8-Pin Molded Dual-In-Line Package
Order Number LMC6081AIN, LMC6081AMN or LMC6081IN
NS Package Number N08E
11
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LMC6081 Precision CMOS Single Operational Amplifier
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1. Life support devices or systems are devices or sysdevice or system whose failure to perform can be reatems which, (a) are intended for surgical implant into
sonably expected to cause the failure of the life support
the body, or (b) support or sustain life, and whose faildevice or system, or to affect its safety or effectiveness.
ure to perform when properly used in accordance
with instructions for use provided in the labeling, can
be reasonably expected to result in a significant injury
to the user.
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Email: [email protected]
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