LMC6082 Datasheet, PDF (12/22 Pages) National Semiconductor (TI) – Precision CMOS Dual Operational Amplifier

LMC6082
SNOS630D – AUGUST 2000 – REVISED MARCH 2013
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Figure 28. Example of Guard Ring in P.C. Board Layout
Inverting Amplifier
Non-Inverting Amplifier
Follower
Figure 29. 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 30.
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 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.
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