LMC6042
CMOS Dual Micropower Operational Amplifier
General Description
Ultra-low power consumption and low input-leakage current
are the hallmarks of the LMC6042. Providing input currents
of only 2 fA typical, the LMC6042 can operate from a single
supply, has output swing extending to each supply rail, and
an input voltage range that includes ground.
The LMC6042 is ideal for use in systems requiring ultra-low
power consumption. In addition, the insensitivity to latch-up,
high output drive, and output swing to ground without requir-
ing
external
pull-down
resistors
make
it
ideal
for
single-supply battery-powered systems.
Other applications for the LMC6042 include bar code reader
amplifiers, magnetic and electric field detectors, and
hand-held electrometers.
This device is built with National's advanced Double-Poly
Silicon-Gate CMOS process.
See the LMC6041 for a single, and the LMC6044 for a quad
amplifier with these features.
Features
n
Low supply current:
10 A/Amp (typ)
n
Operates from 4.5V to 15V single supply
n
Ultra low input current:
2 fA (typ)
n
Rail-to-rail output swing
n
Input common-mode range includes ground
Applications
n
Battery monitoring and power conditioning
n
Photodiode and infrared detector preamplifier
n
Silicon based transducer systems
n
Hand-held analytic instruments
n
pH probe buffer amplifier
n
Fire and smoke detection systems
n
Charge amplifier for piezoelectric transducers
Connection Diagram
Ordering Information
Package
Temperature
Transport
Media
Range
NSC
Industrial
Drawing
-40C to +85C
8-Pin
LMC6042AIM
M08A
Rail
Small Outline
LMC6042IM
Tape and Reel
8-Pin
LMC6042AIN
N08E
Rail
Molded DIP
LMC6042IN
8-Pin DIP/SO
DS011137-1
August 1999
LMC6042
CMOS
Dual
Micropower
Operational
Amplifier
1999 National Semiconductor Corporation
DS011137
www.national.com
Absolute Maximum Ratings
(Note 1)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
Differential Input Voltage
Supply Voltage
Supply Voltage (V
+
- V
-
)
16V
Output Short Circuit to V
+
(Note 12)
Output Short Circuit to V
-
(Note 2)
Lead Temperature
(Soldering, 10 seconds)
260C
Current at Input Pin
5 mA
Current at Output Pin
18 mA
Current at Power Supply Pin
35 mA
Power Dissipation
(Note 3)
Storage Temperature Range
-65C to +150C
Junction Temperature (Note 3)
110C
ESD Tolerance (Note 4)
500V
Voltage at Input/Output Pin
(V
+
) + 0.3V, (V
-
) - 0.3V
Operating Ratings
Temperature Range
LMC6042AI, LMC6042I
-40C
T
J
+85C
Supply Voltage
4.5V
V
+
15.5V
Power Dissipation
(Note 10)
Thermal Resistance (
JA
), (Note 11)
8-Pin DIP
101C/W
8-Pin SO
165C/W
Electrical Characteristics
Unless otherwise spec ified, all limits guaranteed for T
A
= T
J
= 25C. Boldface limits apply at the temperature extremes. V
+
=
5V, V
-
= 0V, V
CM
= 1.5V, V
O
= V
+
/2 and R
L
>
1M unless otherwise specified.
Typical
LMC6042AI
LMC6042I
Units
Symbol
Parameter
Conditions
(Note 5)
Limit
Limit
(Limit)
(Note 6)
(Note 6)
V
OS
Input Offset Voltage
1
3
6
mV
3.3
6.3
Max
TCV
OS
Input Offset Voltage
1.3
V/C
Average Drift
I
B
Input Bias Current
0.002
4
4
pA (Max)
I
OS
Input Offset Current
0.001
2
2
pA (Max)
R
IN
Input Resistance
>
10
Tera
CMRR
Common Mode
0V
V
CM
12.0V
75
68
62
dB
Rejection Ratio
V
+
= 15V
66
60
Min
+PSRR
Positive Power Supply
5V
V
+
15V
75
68
62
dB
Rejection Ratio
V
O
= 2.5V
66
60
Min
-PSRR
Negative Power Supply
0V
V
-
-10V
94
84
74
dB
Rejection Ratio
V
O
= 2.5V
83
73
Min
CMR
Input Common-Mode
V
+
= 5V and 15V
-0.4
-0.1
-0.1
V
Voltage Range
For CMRR
50 dB
0
0
Max
V
+
-1.9V
V
+
- 2.3V
V
+
- 2.3V
V
V
+
- 2.5V
V
+
- 2.4V
Min
A
V
Large Signal
R
L
= 100 k
(Note 7)
Sourcing
1000
400
300
V/mV
Voltage Gain
300
200
Min
Sinking
500
180
90
V/mV
120
70
Min
R
L
= 25 k
(Note 7)
Sourcing
1000
200
100
V/mV
160
80
Min
Sinking
250
100
50
V/mV
60
40
Min
www.national.com
2
Electrical Characteristics
(Continued)
Unless otherwise spec ified, all limits guaranteed for T
A
= T
J
= 25C. Boldface limits apply at the temperature extremes. V
+
=
5V, V
-
= 0V, V
CM
= 1.5V, V
O
= V
+
/2 and R
L
>
1M unless otherwise specified.
Typical
LMC6042AI
LMC6042I
Units
Symbol
Parameter
Conditions
(Note 5)
Limit
Limit
(Limit)
(Note 6)
(Note 6)
V
O
Output Swing
V
+
= 5V
4.987
4.970
4.940
V
R
L
= 100 k
to V
+
/2
4.950
4.910
Min
0.004
0.030
0.060
V
0.050
0.090
Max
V
+
= 5V
4.980
4.920
4.870
V
R
L
= 25 k
to V
+
/2
4.870
4.820
Min
0.010
0.080
0.130
V
0.130
0.180
Max
V
+
= 15V
14.970
14.920
14.880
V
R
L
= 100 k
to V
+
/2
14.880
14.820
Min
0.007
0.030
0.060
V
0.050
0.090
Max
V
+
= 15V
14.950
14.900
14.850
V
R
L
= 25 k
to V
+
/2
14.850
14.800
Min
0.022
0.100
0.150
V
0.150
0.200
Max
I
SC
Output Current
Sourcing, V
O
= 0V
22
16
13
mA
V
+
= 5V
10
8
Min
Sinking, V
O
= 5V
21
16
13
mA
8
8
Min
I
SC
Output Current
Sourcing, V
O
= 0V
40
15
15
mA
V
+
= 15V
10
10
Min
Sinking, V
O
= 13V
39
24
21
mA
(Note 12)
8
8
Min
I
S
Supply Current
Both Amplifiers
20
34
45
A
V
O
= 1.5V
39
50
Max
Both Amplifiers
26
44
56
A
V
+
= 15V
51
65
Max
AC Electrical Characteristics
Unless otherwise specified, all limits guaranteed for T
A
= T
J
= 25C. Boldface limits apply at the temperature extremes. V
+
=
5V, V
-
= 0V, V
CM
= 1.5V, V
O
= V
+
/2 and R
L
>
1M unless otherwise specified.
Typ
LMC6042AI
LMC6042I
Units
Symbol
Parameter
Conditions
(Note 5)
Limit
Limit
(Limit)
(Note 6)
(Note 6)
SR
Slew Rate
(Note 8)
0.02
0.015
0.010
V/s
0.010
0.007
Min
GBW
Gain-Bandwidth Product
100
kHz
m
Phase Margin
60
Deg
Amp-to-Amp Isolation
(Note 9)
115
dB
e
n
Input-Referred
Voltage Noise
f = 1 kHz
83
i
n
Input-Referred
Current Noise
f = 1 kHz
0.0002
www.national.com
3
AC Electrical Characteristics
(Continued)
Unless otherwise specified, all limits guaranteed for T
A
= T
J
= 25C. Boldface limits apply at the temperature extremes. V
+
=
5V, V
-
= 0V, V
CM
= 1.5V, V
O
= V
+
/2 and R
L
>
1M unless otherwise specified.
Typ
LMC6042AI
LMC6042I
Units
Symbol
Parameter
Conditions
(Note 5)
Limit
Limit
(Limit)
(Note 6)
(Note 6)
T.H.D.
Total Harmonic Distortion
f = 1 kHz, A
V
= -5
R
L
= 100 k
, V
O
= 2 V
PP
0.01
%
5V Supply
Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Conditions 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 operation. Continuous short circuit operation at elevated ambient temperature can result in exceeding the maximum allowed
junction temperature of 110C. Output currents in excess of
30 mA over long term may adversely affect reliability.
Note 3: The maximum power dissipation is a function of T
J(Max)
,
JA
, and T
A
. The maximum allowable power dissipation at any ambient temperature is P
D
= (T
J(Max)
- T
A
)/
JA
.
Note 4: Human body model, 1.5 k
in series with 100 pF.
Note 5: Typical values represent the most likely parametric norm.
Note 6: All limits are guaranteed at room temperature (standard type face) or at operating temperature extremes (bold face type).
Note 7: V
+
= 15V, V
CM
= 7.5V and R
L
connected to 7.5V. For Sourcing tests, 7.5V
V
O
11.5V. For Sinking tests, 2.5V
V
O
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: Input referred V
+
= 15V and R
L
= 100 k
connected to V
+
/2. Each amp excited in turn with 100 Hz to produce V
O
= 12 V
PP
.
Note 10: For operating at elevated temperatures the device must be derated based on the thermal resistance
JA
with P
D
= (T
J
- T
A
)/
JA
.
Note 11: All numbers apply for packages soldered directly into a PC board.
Note 12: Do not connect output to V
+
when V
+
is greater than 13V or reliability may be adversely affected.
Typical Performance Characteristics
V
S
=
7.5V, T
A
= 25C unless otherwise specified
Supply Current vs
Supply Voltage
DS011137-19
Offset Voltage vs
Temperature of Five
Representative Units
DS011137-20
Input Bias Current
vs Temperature
DS011137-21
Input Bias Current
vs Input Common-Mode
Voltage
DS011137-22
Input Common-Mode
Voltage Range
vs Temperature
DS011137-23
Output Characteristics
Current Sinking
DS011137-24
www.national.com
4
Typical Performance Characteristics
V
S
=
7.5V, T
A
= 25C unless otherwise specified (Continued)
Output Characteristics
Current Sourcing
DS011137-25
Input Voltage Noise
vs Frequency
DS011137-26
Crosstalk Rejection
vs Frequency
DS011137-27
CMRR vs Frequency
DS011137-28
CMRR vs Temperature
DS011137-29
Power Supply Rejection
Ratio vs Frequency
DS011137-30
Open-Loop Voltage
Gain vs Temperature
DS011137-31
Open-Loop
Frequency Response
DS011137-32
Gain and Phase
Responses vs
Load Capacitance
DS011137-33
www.national.com
5
Typical Performance Characteristics
V
S
=
7.5V, T
A
= 25C unless otherwise specified (Continued)
Gain and Phase
Response vs
Temperature
DS011137-34
Gain Error
(V
OS
vs V
OUT
)
DS011137-35
Common-Mode Error vs
Common-Mode Voltage of
3 Representative Units
DS011137-36
Non-Inverting Slew
Rate vs Temperature
DS011137-37
Inverting Slew Rate
vs Temperature
DS011137-38
Non-Inverting Large
Signal Pulse Response
(A
V
= +1)
DS011137-39
Non-Inverting Small
Signal Pulse Response
DS011137-40
Inverting Large-Signal
Pulse Response
DS011137-41
Inverting Small Signal
Pulse Response
DS011137-42
www.national.com
6
Typical Performance Characteristics
V
S
=
7.5V, T
A
= 25C unless otherwise specified (Continued)
Applications Hints
AMPLIFIER TOPOLOGY
The LMC6042 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 compensa-
tion design techniques are incorporated to maintain stability
over a wider range of operating conditions than traditional
micropower op-amps. These features make the LMC6042
both easier to design with, and provide higher speed than
products typically found in this ultra-low power class.
COMPENSATING FOR INPUT CAPACITANCE
It is quite common to use large values of feedback resis-
tance with amplifiers with ultra-low input curent, like the
LMC6042.
Although the LMC6042 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, photo-
diodes, and circuit board parasitics, reduce phase margins.
When high input impedances are demanded, guarding of the
LMC6042 is suggested. Guarding input lines will not only re-
duce 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. Place a capacitor, C
f
, around the feed-
back resistor (as in
Figure 1 ) such that:
or
R1 C
IN
R2 C
f
Since it is often difficult to know the exact value of C
IN
, C
f
can
be experimentally adjusted so that the desired pulse re-
sponse is achieved. Refer to the LMC660 and the LMC662
for a more detailed discussion on compensating for input ca-
pacitance.
CAPACITIVE LOAD TOLERANCE
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 ca-
pacitive load. This pole induces phase lag at the unity-gain
crossover frequency of the amplifier resulting in either an os-
cillatory or underdamped pulse response. With a few exter-
nal components, op amps can easily indirectly drive capaci-
tive loads, as shown in
Figure 2.
In the circuit of
Figure 2, R1 and C1 serve to counteract the
loss of phase margin by feeding the high frequency compo-
Stability vs Capacitive Load
DS011137-43
Stability vs Capacitive Load
DS011137-44
DS011137-5
FIGURE 1. Cancelling the Effect of Input Capacitance
DS011137-6
FIGURE 2. LMC6042 Noninverting Gain of 10 Amplifier,
Compensated to Handle Capacitive Loads
www.national.com
7
Applications Hints
(Continued)
nent of the output signal back to the amplifier's inverting in-
put, 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 10 A or more will significantly improve capaci-
tive 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 resis-
tor (see Electrical Characteristics).
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 LMC6042, typically less
than 2 fA, it is essential to have an excellent layout. Fortu-
nately, 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 accept-
ably 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 LMC6042's inputs and the
terminals of capacitors, diodes, conductors, resistors, relay
terminals etc. connected to the op-amp's inputs, as in
Figure
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 10
12
, which is nor-
mally 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 LMC6042's
actual performance. However, if a guard ring is held within 5
mV of the inputs, then even a resistance of 10
11
would
cause only 0.05 pA of leakage current. See
Figure 5 for typi-
cal connections of guard rings for standard op-amp
configurations.
DS011137-18
FIGURE 3. Compensating for Large
Capacitive Loads with a Pull Up Resistor
DS011137-7
FIGURE 4. Example of Guard Ring
in P.C. Board Layout
DS011137-8
Inverting Amplifier
DS011137-10
Non-Inverting Amplifier
DS011137-9
Follower
FIGURE 5. Typical Connections of Guard Rings
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8
Applications Hints
(Continued)
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 in-
sulator. Air is an excellent insulator. In this case you may
have to forego some of the advantages of PC board con-
struction, but the advantages are sometimes well worth the
effort of using point-to-point up-in-the-air wiring. See
Figure
6.
Typical Single-Supply Applications
(V
+
= 5.0 V
DC
)
The extremely high input impedance, and low power con-
sumption, of the LMC6042 make it ideal for applications that
require battery-powered instrumentation amplifiers. Ex-
amples of these types of applications are hand-held pH
probes, analytic medical instruments, magnetic field detec-
tors, gas detectors, and silicon based pressure transducers.
The circuit in
Figure 7 is recommended for applications
where the common-mode input range is relatively low and
the differential gain will be in the range of 10 to 1000. This
two op-amp instrumentation amplifier features an indepen-
dent adjustment of the gain and common-mode rejection
trim, and a total quiescent supply current of less than 20 A.
To maintain ultra-high input impedance, it is advisable to use
ground rings and consider PC board layout an important part
of the overall system design (see Printed-Circuit-Board Lay-
out for High Impedance Work). Referring to
Figure 7, the in-
put voltages are represented as a common-mode input V
CM
plus a differential input V
D
.
Rejection of the common-mode component of the input is
accomplished by making the ratio of R1/R2 equal to R3/R4.
So that where,
A suggested design guideline is to minimize the difference of
value between R1 through R4. This will often result in im-
proved resistor tempco, amplifier gain, and CMRR over tem-
perature. If RN = R1 = R2 = R3 = R4 then the gain equation
can be simplified:
Due to the "zero-in, zero-out" performance of the LMC6042,
and output swing rail-rail, the dynamic range is only limited to
the input common-mode range of 0V to V
S
- 2.3V, worst
case at room temperature. This feature of the LMC6042
makes it an ideal choice for low-power instrumentation sys-
tems.
A complete instrumentation amplifier designed for a gain of
100 is shown in
Figure 8. Provisions have been made for low
sensitivity trimming of CMRR and gain.
DS011137-11
(Input pins are lifted out of PC board and soldered directly to components.
All other pins connected to PC board.)
FIGURE 6. Air Wiring
DS011137-12
FIGURE 7. Two Op-Amp Instrumentation Amplifier
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9
Typical Single-Supply Applications
(V
+
= 5.0 V
DC
) (Continued)
DS011137-13
FIGURE 8. Low-Power Two-Op-Amp
Instrumentation Amplifier
DS011137-14
FIGURE 9. Low-Leakage Sample and Hold
DS011137-15
FIGURE 10. Instrumentation Amplifier
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10
Typical Single-Supply Applications
(V
+
= 5.0 V
DC
) (Continued)
DS011137-16
FIGURE 11. 1 Hz Square Wave Oscillator
DS011137-17
FIGURE 12. AC Coupled Power Amplifier
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11
Physical Dimensions
inches (millimeters) unless otherwise noted
8-Pin Small Outline Package
Order Number LMC6042AIM or LMC6042IM
NS Package Number M08A
8-Pin Molded Dual-In-Line Package
Order Number LMC6042AIN or LMC6042IN
NS Package Number N08E
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12
Notes
LIFE SUPPORT POLICY
NATIONAL'S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT
DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT AND GENERAL
COUNSEL OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein:
1. Life support devices or systems are devices or
systems which, (a) are intended for surgical implant
into the body, or (b) support or sustain life, and
whose failure 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.
2. A critical component is any component of a life
support device or system whose failure to perform
can be reasonably expected to cause the failure of
the life support device or system, or to affect its
safety or effectiveness.
National Semiconductor
Corporation
Americas
Tel: 1-800-272-9959
Fax: 1-800-737-7018
Email: support@nsc.com
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Tel: 81-3-5639-7560
Fax: 81-3-5639-7507
www.national.com
LMC6042
CMOS
Dual
Micropower
Operational
Amplifier
National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications.
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