LMC6062

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SNOS631D – NOVEMBER 1994 – REVISED MARCH 2013

Figure 27. Example of Guard Ring in P.C. Board Layout

(a) Inverting Amplifier

(b) Non-Inverting Amplifier

(c) Follower

Figure 28. 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 29.

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.

Copyright © 1994–2013, Texas Instruments Incorporated

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