LMC6082AMN NSC [National Semiconductor], LMC6082AMN Datasheet - Page 9

• Manufacturer Part Number: LMC6082AMN
• Description: Precision CMOS Dual Operational Amplifier
• Manufacturer: NSC [National Semiconductor]

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
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
wiring. See Figure 6 .
FIGURE 5. Typical Connections of Guard Rings
of
Non-Inverting Amplifier
using
Inverting Amplifier
Follower
point-to-point
(Continued)
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DS011297-7
up-in-the-air
DS011297-8
9
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 cur-
rent required to trigger the SCR gate lead. The LMC6062
and LMC6082 are designed to withstand 100 mA surge cur-
rent 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.
(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 k
put 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
), 0.01% gain accuracy at A
DC
2
)
provides a simple means of adjusting gain
imbalance in bridge source resistance. In-
FIGURE 6. Air Wiring
V
= 1000, excellent
7
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is an initial
DS011297-10