lmc6082aimx National Semiconductor Corporation, lmc6082aimx Datasheet - Page 10

• Manufacturer Part Number: lmc6082aimx
• Description: Precision Cmos Dual Operational Amplifier
• Manufacturer: National Semiconductor Corporation

www.national.com
Applications Hints
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
FIGURE 4. Example of Guard Ring in P.C. Board
FIGURE 5. Typical Connections of Guard Rings
Non-Inverting Amplifier
Inverting Amplifier
Follower
Layout
(Continued)
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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 con-
struction, but the advantages are sometimes well worth the
effort
wiring. See Figure 6.
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
current required to trigger the SCR gate lead. The LMC6062
and LMC6082 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 cur-
rent 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 suscepti-
bility.
(Input pins are lifted out of PC board and soldered directly to components.
All other pins connected to PC board).
Typical Single-Supply Applications
(V
The extremely high input impedance, and low power con-
sumption, of the LMC6082 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.
Figure 7 shows an instrumentation amplifier that features
high differential and common mode input resistance
(
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. R
over a wide range without degrading CMRR. R
trim used to maximize CMRR without using super precision
matched resistors. For good CMRR over temperature, low
drift resistors should be used.
>
+
10
= 5.0 V
14
Ω), 0.01% gain accuracy at A
of
DC
2
)
provides a simple means of adjusting gain
using
FIGURE 6. Air Wiring
point-to-point
V
= 1000, excellent
7
up-in-the-air
is an initial
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