LMC6582 Dual/LMC6584 Quad
Low Voltage, Rail-To-Rail Input and Output CMOS
Operational Amplifier
General Description
The LMC6582/4 is a high performance operational amplifier
which can operate over a wide range of supply voltages with
guaranteed specifications at 1.8V, 2.2V, 3V, 5V, and 10V.
The LMC6582/4 provides an input common-mode voltage
range that exceeds both supplies. The rail-to-rail output
swing of the amplifier assures maximum dynamic signal
range. This rail-to-rail performance of the amplifier, com-
bined with its high open-loop voltage gain makes it unique
among rail-to-rail CMOS amplifiers. The LMC6582/4 is an
excellent choice for circuits where the input common-mode
voltage range is a concern.
The LMC6582/4 has been designed specifically to improve
system performance in low voltage applications. Guaranteed
operation down to 1.8V means that this family of amplifiers
can operate at the end of discharge (EOD) voltages of sev-
eral popular batteries. The amplifier’s 80 fAinput current, 0.5
mV offset voltage, and 82 dB CMRR maintain accuracy in
battery-powered systems.
For a single, dual or quad CMOS amplifier with similar specs
and a powerdown mode, refer to the LMC6681/2/4
datasheet.
Features
(Typical unless otherwise noted)
nGuaranteed Specs at 1.8V, 2.2V, 3V, 5V, 10V
nRail-to-Rail Input Common-Mode Voltage Range
nRail-to-Rail Output Swing
(within 10 mV of supply rail, @V
S
=3V and R
L
=10 kΩ)
nCMRR and PSRR: 82 dB
nUltra Low Input Current: 80 fA
nHigh Voltage Gain (V
S
=3V, R
L
=10 kΩ): 120 dB
nUnity Gain Bandwidth: 1.2 MHz
Applications
nBattery Operated Systems
nSensor Amplifiers
nPortable Communication Devices
nMedical Instrumentation
nLevel Detectors, Sample-and-Hold Circuits
nBattery Monitoring
Connection Diagrams
8-Pin DIP/SO
DS012041-1
Top View
14-Pin DIP/SO
DS012041-2
Top View
May 1995
LMC6582 Dual/LMC6584 Quad Low Voltage, Rail-To-Rail Input and Output CMOS Operational
Amplifier
© 1999 National Semiconductor Corporation DS012041 www.national.com
Ordering Information
Package Temperature Range NSC Transport
Industrial, −40˚C to +85˚C Drawing Media
8-pin Molded DIP LMC6582AIN, LMC6582BIN N08E Rails
8-pin Small Outline LMC6582AIM, LMC6582BIM M08A Rails
LMC6582AIMX, LMC6582BIMX M08A Tape and Reel
14-pin Molded DIP LMC6584AIN, LMC6584BIN N14A Rails
14-pin Small Outline LMC6584AIM, LMC6584BIM M14A Rails
LMC6584AIMX, LMC6584BIMX M14A Tape and Reel
www.national.com 2
Absolute Maximum Ratings (Note 1)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
ESD Tolerance (Note 2) 2 kV
Differential Input Voltage ±Supply Voltage
Voltage at Input/Output Pin (V
+
) +0.3V, (V
−
) −0.3V
Supply Voltage (V
+
−V
−
) 12V
Current at Input Pin (Note 11) ±5mA
Current at Output Pin (Note 3) ±30 mA
Current at Power Supply Pin 35 mA
Lead Temp. (soldering, 10 sec.) 260˚C
Storage Temperature Range −65˚C to +150˚C
Junction Temperature (Note 4) 150˚C
Operating Ratings (Note 1)
Supply Voltage 1.8V ≤V
S
≤10V
Junction Temperature Range
LMC6582AI, LMC6582BI −40˚C ≤T
J
≤+85˚C
LMC6584AI, LMC6584BI −40˚C ≤T
J
≤+85˚C
Thermal Resistance (θ
JA
)
N Package, 8-pin Molded DIP 108˚C/W
M Package, 8-pin Surface Mount 172˚C/W
N Package, 14-pin Molded DIP 88˚C/W
M Package, 14-pin Surface Mount 126˚C/W
3V DC Electrical Characteristics
Unless otherwise specified, all limits guaranteed for T
J
=25˚C, V
+
=3.0V, V
−
=0V, V
CM
=V
O
=V
+
/2 and R
L
>1MΩ.Bold-
face limits apply at the temperature extremes.
LMC6582AI LMC6582BI
Symbol Parameter Conditions Typ LMC6584AI LMC6584BI Units
(Note 5) Limit Limit
(Note 6) (Note 6)
V
OS
Input Offset Voltage 0.5 1 3 mV
2.5 4.5 max
TCV
OS
Input Offset Voltage 1.5 µV/˚C
Average Drift
I
B
Input Current (Note 12) 0.08 20 20 pA max
I
OS
Input Offset Current (Note 12) 0.04 10 10 pA max
R
IN
Input Resistance >1 Tera Ω
C
IN
Input Capacitance 3 pF
CMRR Common Mode (Note 13) 82 70 65 dB
Rejection Ratio 65 62 min
PSRR Power Supply ±1.5V ≤V
S
≤±2.5V 82 70 65 dB
Rejection Ratio V
O
=V
+
/2 =V
CM
65 62 min
V
CM
Input Common Mode CMRR >50 dB 3.23 3.18 3.18 V
Voltage Range 3.00 3.00 min
−0.3 −0.18 −0.18 V
0.00 0.00 max
A
V
Large Signal
Voltage Gain R
L
=600Ω(Notes 7, 12) 70 10 10 V/mV
R
L
=10 kΩ(Notes 7, 12) 1000 12 12 V/mV
V
O
Output Swing R
L
=600Ωto V
+
/2 2.87 2.70 2.70 V
2.58 2.58 min
0.15 0.3 0.3 V
0.42 0.42 max
R
L
=2kΩto V
+
/2 2.95 2.85 2.85 V
2.79 2.79 min
0.05 0.15 0.15 V
0.21 0.21 max
R
L
=10 kΩto V
+
/2 2.99 2.94 2.94 V
2.91 2.91 min
0.01 0.04 0.04 V
0.05 0.05 max
www.national.com3
3V DC Electrical Characteristics (Continued)
Unless otherwise specified, all limits guaranteed for T
J
=25˚C, V
+
=3.0V, V
−
=0V, V
CM
=V
O
=V
+
/2 and R
L
>1MΩ.Bold-
face limits apply at the temperature extremes.
LMC6582AI LMC6582BI
Symbol Parameter Conditions Typ LMC6584AI LMC6584BI Units
(Note 5) Limit Limit
(Note 6) (Note 6)
I
SC
Output Short Circuit Sourcing, V
O
=0V 20 9.0 9.0 mA
Current 6.7 6.7 min
Sinking, V
O
=3V 12 6.0 6.0 mA
4.5 4.5 min
I
S
Supply Current Dual, LMC6582 1.4 2.26 2.26 mA
V
CM
=1.5V 2.75 2.75 max
Quad, LMC6584 2.8 4.52 4.52 mA
V
CM
=1.5V 5.42 5.42 max
1.8V and 2.2V DC Electrical Characteristics
Unless otherwise specified, all limits guaranteed for T
J
=25˚C, V
+
=1.8V and 2.2V, V
−
=0V, V
CM
=V
O
=V
+
/2 and R
L
>1M
Ω.Boldface limits apply at the temperature extremes.
LMC6582AI LMC6582BI
Symbol Parameter Conditions Typ LMC6584AI LMC6584BI Units
(Note 5) Limit Limit
(Note 6) (Note 6)
V
OS
Input Offset Voltage V
+
=1.8V, V
CM
=1.5V 0.5 3 10 mV
max
V
+
=2.2V, V
CM
=1.5V 0.5 2 6 mV
3.8 7.8 max
TCV
os
Input Offset Voltage V
+
=2.2V 1.5 µV/˚C
Average Drift
I
B
Input Current V
+
=2.2V (Note 12) 0.08 20 20 pA max
I
OS
Input Offset Current V
+
=2.2V (Note 12) 0.04 10 10 pA max
CMRR Common Mode V
+
=2.2V, (Note 13) 82 60 60 dB min
Rejection Ratio V
+
=1.8V, (Note 13) 82 50 50 dB min
PSRR Power Supply ±1.1V ≤V
S
≤±5V, 82 70 65 dB
Rejection Ratio V
O
=V
+
/2 =V
CM
65 62 min
V
CM
Input Common Mode V
+
=2.2V
CMRR >40 dB 2.38 2.2 2.2 V min
Voltage Range −0.15 0.0 0.0 V max
V
+
=1.8V
CMRR >40 dB 1.98 1.8 1.8 V min
−0.10 0.0 0.0 V max
V
O
Output Swing V
+
=2.2V 2.15 2.0 2.0 V
R
L
=2kΩto V
+
/2 1.88 1.88 min
0.05 0.2 0.2 V
0.32 0.32 max
V
+
=1.8V 1.75 1.6 1.6 V
R
L
=2kΩto V
+
/2 1.44 1.44 min
0.05 0.2 0.2 V
0.36 0.36 max
I
S
Supply Current Dual, LMC6582 1.4 2.2 2.2 mA
V
CM
=1.5V 2.7 2.7 max
Quad, LMC6584 2.8 4.4 4.4 mA
V
CM
=1.5V 5.3 5.3 max
www.national.com 4
5V DC Electrical Characteristics
Unless otherwise specified, all limits guaranteed for T
J
=25˚C, V
+
=5.0V, V
−
=0V, V
CM
=V
O
=V
+
/2 and R
L
>1MΩ.Bold-
face limits apply at the temperature extremes.
LMC6582AI LMC6582BI
Symbol Parameter Conditions Typ LMC6584AI LMC6584BI Units
(Note 5) Limit Limit
(Note 6) (Note 6)
V
OS
Input Offset Voltage V
CM
=1.5V 0.5 1 3 mV
2.5 4.5 max
TCV
OS
Input Offset Voltage 1.5 µV/˚C
Average Drift
I
B
Input Current (Note 12) 0.08 20 20 pA max
I
OS
Input Offset Current (Note 12) 0.04 10 10 pA max
R
IN
Input Resistance >1 Tera Ω
C
IN
Input Capacitance 3 pF
CMRR Common Mode (Note 13) 82 70 65 dB
Rejection Ratio 65 62 min
PSRR Power Supply ±1.5V ≤V
S
≤±2.5V, 82 70 65 dB
Rejection Ratio V
O
=V
+
/2 =V
CM
65 62 min
V
CM
Input Common Mode CMRR >50 dB 5.3 5.18 5.18 V
Voltage Range 5.00 5.00 min
−0.3 −0.18 −0.18 V
0.00 0.00 max
V
O
Output Swing R
L
=2kΩto V
+
/2 4.9 4.85 4.85 V
4.58 4.58 min
0.05 0.2 0.2 V
0.28 0.28 max
I
S
Supply Current Dual, LMC6582 1.5 2.48 2.48 mA
V
CM
=1.5V 3.00 3.00 max
Quad, LMC6584 3.0 4.96 4.96 mA
V
CM
=1.5V 6.00 6.00 max
www.national.com5
10V DC Electrical Characteristics
Unless otherwise specified, all limits guaranteed for T
J
=25˚C, V
+
=10.0V, V
−
=0V, V
CM
=V
O
=V
+
/2 and R
L
>1MΩ.
Boldface limits apply at the temperature extremes.
LMC6582AI LMC6582BI
Symbol Parameter Conditions Typ LMC6584AI LMC6584BI Units
(Note 5) Limit Limit
(Note 6) (Note 6)
V
OS
Input Offset Voltage V
CM
=1.5V 0.5 1.5 3.5 mV
3.0 5.0 max
TCV
OS
Input Offset Voltage 1.5 µV/˚C
Average Drift
I
B
Input Current (Note 12) 0.08 20 20 pA max
I
OS
Input Offset Current (Note 12) 0.04 10 10 pA max
R
IN
Input Resistance >1 Tera Ω
C
IN
Input Capacitance 3 pF
CMRR Common Mode (Note 13) 82 65 65 dB
Rejection Ratio 62 62 min
PSRR Power Supply ±1.1V ≤V
+
≤±5V, 82 70 65 dB
Rejection Ratio V
O
=V
+
/2 =V
CM
65 62 min
V
CM
Input Common Mode CMRR >50 dB 10.30 10.18 10.18 V
Voltage Range 10.00 10.00 min
−0.30 −0.18 −0.18 V
0.00 0.00 max
V
O
Output Swing R
L
=2kΩto V
+
/2 9.93 9.7 9.7 V
9.58 9.58 min
0.08 0.3 0.3 V
0.42 0.42 max
A
V
Large Signal R
L
=2kΩto V
+
/2 Sourcing 89 25 25 V/mV
Voltage Gain (Note 12) Sinking 224 25 25 V/mV
I
SC
Output Short Circuit Sourcing, V
O
=0V 65 30 30 mA
Current (Note 14) 22 22 min
Sinking, V
O
=10V 70 30 30 mA
(Note 14) 22 22 min
I
S
Supply Current Dual, LMC6582 1.6 3.0 3.0 mA
V
CM
=1.5V 3.6 3.6 max
Quad, LMC6584 3.2 6.0 6.0 mA
V
CM
=1.5V 7.2 7.2 max
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AC Electrical Characteristics
Unless otherwise specified, all limits guaranteed for T
J
=25˚C, V
+
=3V, V
−
=0V, V
CM
=V
O
=V
+
/2 and R
L
>1MΩ.Bold-
face limits apply at the temperature extremes.
Symbol Parameter Conditions Typ
(Note 5)
LMC6582AI LMC6582BI
Units
LMC6584AI LMC6584BI
Limit Limit
(Note 6) (Note 6)
SR Slew Rate (Note 8) 1.2 0.7 0.7 V/µs
min
0.55 0.55
V
+
=10V, (Note 10) 1.2 0.7 0.7
0.55 0.55
GBW Gain-Bandwidth Product 1.2 MHz
φ
m
Phase Margin 50 Deg
G
m
Gain Margin 12 dB
Amp-to-Amp Isolation V
+
=10V (Note 9) 130 dB
e
n
Input-Referred f =1 kHz 30
Voltage Noise V
CM
=0.5V
i
n
Input-Referred f =1 kHz 0.5
Current Noise
T.H.D. Total Harmonic Distortion f =1 kHz, A
V
=+1 0.01 %
R
L
=10 kΩ,V
O
=2V
p-p
Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating ratings indicate conditions for which the device is in-
tended to be functional, but specific performance is not guaranteed. For guaranteed specifications and the test conditions, see the electrical characteristics.
Note 2: Human body model, 1.5 kΩin series with 100 pF.
Note 3: Applies to both single-supply and split-supply operation. Continous short circuit operation at elevated ambient temperature can result in exceeding the maxi-
mum allowed junction temperature of 150˚C. Output current in excess of ±30 mA over long term may adversely affect reliability.
Note 4: 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)
−T
A
)/θJA. All numbers apply for packages soldered directly into a PC board.
Note 5: Typical Values represent the most likely parametric norm.
Note 6: All limits are guaranteed by testing or statistical analysis.
Note 7: V+=3V, VCM =0.5V. For sourcing and sinking, 0.5V ≤VO≤2.5V.
Note 8: V+=3V. Connected as Voltage Follower with 2V step input, and output is measured from 0.8V to 2.2V. Number specified is the slower of the positive or nega-
tive slew rates.
Note 9: Input referred, V+=10V, and RL=100 kΩconnected to 5V. Each amp excited in turn with 1 kHz to produce VO=2V
PP.
Note 10: V+=10V. Connected as voltage follower with 8V step Input, and output is measured from 2V to 8V. Number specified is the slower of the positive or nega-
tive slew rates.
Note 11: Limiting input pin current is only necessary for input voltages that exceed absolute maximum input voltage ratings.
Note 12: Guaranteed limits are dictated by tester limitations and not device performance. Actual performance is reflected in the typical value.
Note 13: CMRR+and CMRR−are tested, and the number indicated is the lower of the two values. For CMRR+,V
+
/2 <VCM <V+for 1.8V, 2.2V, 3V, 5V, and 10V.
For CMRR−,0<V
CM <V+/2 for 3V, 5V and 10V. For 1.8V and 2.2V, 0.25 <VCM <V+−0.3.
Note 14: V+=10V, VCM =0.5V. For Sourcing tests, 1V ≤VO≤5V. For Sinking tests, 5V ≤VO≤9V.
www.national.com7
Typical Performance Characteristics V
S
+=3V, Single Supply, T
A
=25˚C unless otherwise specified.
Supply Current Per
Amplifier vs
Supply Voltage
DS012041-35
Sourcing Current vs
Output Voltage
DS012041-36
Sinking Current vs
Output Voltage
DS012041-37
Input Voltage Noise vs
Common-Mode Voltage
DS012041-38
∆V
OS
vs V
CM
DS012041-39
∆V
OS
vs V
CM
DS012041-40
Frequency Response
vs Temperature
DS012041-41
Frequency Response
vs R
L
DS012041-42
Input Voltage Noise vs
Frequency
DS012041-43
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Typical Performance Characteristics V
S
+=3V, Single Supply, T
A
=25˚C unless otherwise
specified. (Continued)
CMRR vs Frequency
DS012041-44
Positive PSRR vs
Frequency
DS012041-45
Negative PSRR vs
Frequency
DS012041-46
Crosstalk Rejection
vs Frequency
DS012041-47
Slew Rate vs
Supply Voltage
DS012041-48
Non-Inverting Large
Signal Pulse Response
DS012041-49
Inverting Large Signal
Pulse Response
DS012041-50
Non-Inverting Small
Signal Pulse Response
DS012041-51
Inverting Small Signal
Pulse Response
DS012041-52
www.national.com9
Typical Performance Characteristics V
S
+=3V, Single Supply, T
A
=25˚C unless otherwise
specified. (Continued)
Application Information
1.0 Input Common-Mode Voltage
Range
The LMC6582/4 has a rail-to-rail input common-mode volt-
age range.
Figure 1
shows an input voltage exceeding both
supplies with no resulting phase inversion on the output.
The absolute maximum input voltage at V
+
=3V is 300 mV
beyond either supply rail at room temperature. Voltages
greatly exceeding this absolute maximum rating, as in
Figure
2
, can cause excessive current to flow in or out of the input
pins, possibly affecting reliability. The input current can be
externally limited to ±5 mA, with an input resistor, as shown
in
Figure 3
.2.0 Rail-to-Rail Output
The approximated output resistance of the LMC6582 is 50Ω
sourcing, and 50Ωsinking at V
S
=3V. The maximum output
swing can be estimated as a function of load using the calcu-
lated output resistance.
3.0 Low Voltage Operation
The LMC6582/4 operates at supply voltages of 2.2V and
1.8V. These voltages represent the End of Discharge volt-
ages of several popular batteries. The amplifier can operate
from 1 Lead-Acid or Lithium Ion battery, or 2NiMH, NiCd, or
Carbon-Zinc batteries. Nominal and End of Discharge of
Voltage of several batteries are listed below.
Stability vs
Capacitive Load
DS012041-53
Stability vs
Capacitive Load
DS012041-54
Stability vs
Capacitive Load
DS012041-55
DS012041-3
FIGURE 1. An Input Signal Exceeds the LMC6582
Power Supply Voltages with No Output Phase
Inversion
DS012041-4
FIGURE 2. A ±7.5V Input Signal Greatly
Exceeds the 3V Supply,
Causing No Phase Inversion Due to R
I
DS012041-5
FIGURE 3. Input Current Protection for
Voltages Exceeding the Supply Voltage
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3.0 Low Voltage Operation (Continued)
Battery Type Nominal Voltage End of Discharge
Voltage
NiMH 1.2V 1V
NiCd 1.2V 1V
Lead-Acid 2V 1.8V
Silver Oxide 1.6V 1.3V
Carbon-Zinc 1.5V 1.1V
Lithium 2.6V–3.6V 1.7V–2.4V
At V
S
=2.2V, the LMC6582/4 has a rail-to-rail input
common-mode voltage range.
Figure 4
shows an input volt-
age extending to both supplies and the resulting output.
The amplifier is operational at V
S
=1.8V, with guaranteed in-
put common-mode voltage range, output swing, and CMRR
specs.
Figure 5
shows the response of the LMC6582/4 at V
S
=1.8V.
Figure 6
shows an input voltage exceeding both supplies
with no resulting phase inversion on the output.
4.0 Capacitive Load Tolerance
The LMC6582/4 can typically drive a 100 pF load with V
S
=
10V at unity gain without oscillating. The unity gain follower
is the most sensitive configuration to capacitive load. Direct
capacitive loading reduces the phase margin of op-amps.
The combination of the op-amp’s output impedance and the
capacitive load induces phase lag. This results in either an
underdamped pulse response or oscillation.
Capacitive load compensation can be accomplished using
resistive isolation as shown in
Figure 7
. If there is a resistive
component of the load in parallel to the capacitive compo-
nent, the isolation resistor and the resistive load create a
voltage divider at the output. This introduces a DC error at
the output.
Figure 8
displays the pulse response of the LMC6582 circuit
in
Figure 7
.
DS012041-6
FIGURE 4. The Input Common-Mode Voltage
Range Extends to Both Supplies at V
S
=2.2V
DS012041-7
FIGURE 5. Response of the LMC6582/4
at V
S
=1.8V
DS012041-8
FIGURE 6. An Input Voltage Signal Exceeds
LMC6582/4 Power Supply Voltages of
V
S
=1.8V with No Output Phase Inversion
DS012041-9
FIGURE 7. Resistive Isolation of a 350 pF Capacitive
Load
DS012041-10
FIGURE 8. Pulse Response of the
LMC6582 Circuit in
Figure 7
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4.0 Capacitive Load Tolerance
(Continued)
Another circuit, shown in
Figure 9
, is also used to indirectly
drive capacitive loads. This circuit is an improvement to the
circuit shown
Figure 7
because it provides DC accuracy as
well as AC stability. R1 and C1 serve to counteract the loss
of phase margin by feeding the high frequency component of
the output signal back to the amplifiers inverting input,
thereby preserving phase margin in the overall feedback
loop. The values of R1 and C1 should be experimentally de-
termined by the system designer for the desired pulse re-
sponse. Increased capacitive drive is possible by increasing
the value of the capacitor in the feedback loop.
The pulse response of the circuit shown in
Figure 9
is shown
in
Figure 10
.
5.0 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 input current of the LMC6582/4, typically 80
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 LMC6582/4’s inputs and
the terminals of capacitors, diodes, conductors, resistors, re-
lay terminals, etc. connected to the op-amp’s inputs, as in
Figure 11
. To have a significant effect, guard rings should be
placed in 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
Ω, 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 60 times degradation from the LMC6582/4’s
actual performance. However, if a guard ring is held within 5
mV of the inputs, then even a resistance of 10
11
Ωwould
cause only 0.05 pA of leakage current. See
Figure 12
for
typical connections of guard rings for standard op-amp
configurations.
DS012041-11
FIGURE 9. The LMC6582 Compensated
to Ensure DC Accuracy and AC Stability
DS012041-12
FIGURE 10. Pulse Response of the
LMC6582 Circuit Shown in
Figure 9
DS012041-14
FIGURE 11. Example of Guard Ring in PC Board
Layout
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5.0 Printed-Circuit-Board Layout
for High-Impedance Work (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
13
.
6.0 Compensating for Input
Capacitance
It is quite common to use large values of feedback resis-
tance with amplifiers that have ultra-low input current, like
the LMC6582/4. Large feedback resistors can react with
small values of input capacitance due to transducers, photo-
diodes, and circuits board parasitics to reduce phase
margins.
The effect of input capacitance can be compensated for by
adding a feedback capacitor. The feedback capacitor (as in
Figure 14
), C
F
, is first estimated by:
or
R
1
C
IN
≤
R
2
C
F
which typically provides significant overcompensation.
Printed circuit board stray capacitance may be larger or
smaller than that of a breadboard, so the actual optimum
value for C
F
may be different. The values of C
F
should be
checked on the actual circuit. (Refer to the LMC660 quad
CMOS amplifier data sheet for a more detailed discussion.)
7.0 Spice Macromodel
A Spice Macromodel is available for the LMC6582/4. The
model includes a simulation of:
•Input common-mode voltage range
•Frequency and transient response
•GBW dependence on loading conditions
•Quiescent and dynamic supply current
•Output swing dependence on loading conditions
and many more characteristics as listed on the macromodel
disk.
Contact the National Semiconductor Customer Response
Center at 1-800-272-9959 to obtain an operational amplifier
spice model library disk.
DS012041-15
Inverting Amplifier
DS012041-16
Non-Inverting Amplifier
DS012041-17
Follower
FIGURE 12. Typical Connections of Guard Rings
DS012041-18
FIGURE 13. Air Wiring
DS012041-13
FIGURE 14. Canceling the Effect of Input Capacitance
www.national.com13
Applications
Transducer Interface Circuits
A. PIEZ0ELECTRIC TRANSDUCERS
The LMC6582/4 can be used for processing of transducer
signals as shown in the circuit below. The two 11 MΩresis-
tors provide a path for the DC currents to ground. Since the
resistors are boot-strapped to the output, the AC input resis-
tance of the LMC6582/4 is much higher.
An input current of 80 fAand a CMRR of 82 dB causes an in-
signifcant error offset voltage at the output. The rail-to-rail
performance of the amplifier also provides the maximum dy-
namic range for the transducer signals.
B. PHOTODIODE AMPLIFIERS
Photocells can be used in light measuring instruments. An
error voltage is produced at the output due to the input cur-
rent and the offset voltage of the amplifier. The LMC6582/4
which can be operated off a single battery is an excellent
choice for this application because of its 80 fA input current
and 0.5 mV offset voltage.
Low Voltage Peak Detector
The accuracy of the peak detector is dependent on the leak-
age currents of the diodes and the capacitor, and the
non-idealities of the amplifier. The parameters of the amplifer
which can limit the performance of this circuit are (a) Finite
slew rate (b) Input current, and (c) Maximum output current
of the amplifier.
The input current of the amplifier causes a slow discharge of
the capacitor. This phenomenon is called “drooping”. The
LMC6582/4 has a typical input current of 80 fA. This would
cause the capacitor to droop at a rate of dv/dt =I
B
/C =80 fA/
100 pF =0.8 mV/s. Accuracy in the amplitude measurement
is also maintained by an offset voltage of 0.5 mV, and an
open-loop gain of 120 dB.
Oscillators
For single supply 5V operation, the output of the circuit will
swing 0V to 5V. The voltage divider set by the resistors will
cause the input at the non-inverting terminal of the op-amp to
move
1
⁄
3
(1.67V) of the supply voltage to
2
⁄
3
(3.33V) of the
supply voltage. This voltage behaves as the threshold volt-
age, and causes the capacitor to alternately charge and dis-
charge.
R1 and C1 determine the time constant for the circuit. The
frequency of oscillation, f
OSC
is
where ∆t is the time the amplifier input takes to move from
1.67V to 3.33V. The calculations are shown below.
where τ=RC =0.68 seconds
DS012041-21
FIGURE 15. Transducer Interface Application
DS012041-22
FIGURE 16. LMC6582 Used for Signal Processing
DS012041-23
FIGURE 17. Photodiode Amplifier
DS012041-26
FIGURE 18. Low Voltage Peak Detector
DS012041-27
FIGURE 19. 1 Hz Square-Wave Oscillator
www.national.com 14
Oscillators (Continued)
→t
1
=0.27 seconds
and
→t
2
=0.74 seconds
Then,
z1Hz
LMC6582/4 as a Comparator
Figure 20
shows the application of the LMC6582/4 as a com-
parator. The hysteresis is determined by the ratio of the two
resistors. Since the supply current of the LMC6582/4 is less
than 1 mA per amplifier, it can be used as a low power com-
parator, in applications where the quiescent current is an im-
portant parameter.
Typical propagation delays @V
S
=3V would be on the order
of t
PHL
=6 µs, and t
PLH
=5 µs.
Filters
The filter shown in
Figure 21
is used to process “voice-band”
signals. The bandpass filter has a flatband gain of 40 dB.
The two corner frequencies, f
1
and f
2
, are calculated as:
The LMC6582/4, with its rail-to-rail input common mode volt-
age range and high gain (120 dB typical, R
L
=10 kΩ)isex-
tremely well suited for such filter applications. The rail-to-rail
input range allows for large input signals to be processed
without distortion. The high gain means that the circuit can
provide filtering and gain in one stage, instead of the typical
two stage filter. This implies a reduction in cost, and a sav-
ings of space and power.
This is an illustration of a conceptual use of the LMC6582/4.
The selectivity of the filter can be improved by increasing the
order (number of poles) of the design.
Sample-and-Hold Circuits
When the “switch” is closed during the sample interval,
C
HOLD
charges up to the value of the input signal. When the
“switch” is open, C
HOLD
retains this value as it is buffered by
the high input impedance of the LMC6582/4.
Errors in the “hold” voltage are caused by the input current of
the amplifier, the leakage current of the CD4066, and the
leakage current of the capacitor. While an input current of 80
fAminimizes the accumulation rate for error in the circuit, the
LMC6582/4’s CMRR of 82 dB allows excellent accuracy
throughout the amplifier’s rail-to-rail dynamic capture range.
Battery Monitoring Circuit
DS012041-28
FIGURE 20. Comparator with Hysteresis
DS012041-29
FIGURE 21. Wide-Band Band-Pass Filter
DS012041-31
FIGURE 22. Sample-and-Hold Application
DS012041-33
FIGURE 23. Circuit Used to Sense Charging.
www.national.com15
Battery Monitoring Circuit (Continued) The LMC6582/4 has been optimized for performance at 3V,
and also has guaranteed specs at 1.8V and 2.2V. In portable
applications, the R
Load
represents the laptop/notebook, or
any other computer which the battery is powering. A desired
output voltage can be achieved by manipulating the ratios of
the feedback resistors. During the charging cycle, the cur-
rent flows out of the battery as shown. While during dis-
charge, the current is in the reverse direction. Since the cur-
rent can range from a few milliamperes to amperes, the
amplifier will have to sense a signal below ground during the
discharge cycle. At 3V, the LMC6582/4 can accept a signal
up to 300 mV below ground. The common-mode voltage
range of the LMC6582/4, which extends beyond both rails is
thus a very useful feature in this application.
A typical offset voltage of 0.5 mV, and CMRR of 82 dB main-
tain accuracy in the circuit outputs while the rail-to-rail output
performance allows for a maximum signal range.
DS012041-34
FIGURE 24. Circuit used to Sense Discharging
www.national.com 16
Physical Dimensions inches (millimeters) unless otherwise noted
8-Pin Small Outline Package
Order Number LMC6582AIM or LMC6582BIM
NS Package Number M08A
14-Pin Small Outline Package
Order Number LMC6584AIM or LMC6584BIM
NS Package Number M14A
www.national.com17
Physical Dimensions inches (millimeters) unless otherwise noted (Continued)
8-Pin Molded Dual-In-Line Package
Order Number LMC6582AIN or LMC6582BIN
NS Package Number N08E
14-Pin Molded Dual-In Line Package
Order Number LMC6584AIN or LMC6584BIN
NS Package Number N14A
www.national.com 18
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 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
National Semiconductor
Europe Fax: +49 (0) 1 80-530 85 86
Email: europe.support@nsc.com
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Tel: 65-2544466
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Email: sea.support@nsc.com
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Japan Ltd.
Tel: 81-3-5639-7560
Fax: 81-3-5639-7507
www.national.com
LMC6582 Dual/LMC6584 Quad Low Voltage, Rail-To-Rail Input and Output CMOS 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.
