參數(shù)資料
型號(hào): LMC6081AMN
廠商: NATIONAL SEMICONDUCTOR CORP
元件分類: 運(yùn)算放大器
英文描述: Precision CMOS Single Operational Amplifier
中文描述: OP-AMP, 350 uV OFFSET-MAX, 1.3 MHz BAND WIDTH, PDIP8
封裝: 0.300 INCH, PLASTIC, DIP-8
文件頁數(shù): 8/12頁
文件大?。?/td> 304K
代理商: LMC6081AMN
Applications Hints
(Continued)
ure 4 To have a significant effect, guard rings should be
placed on 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
, 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 100 times degradation from the LMC6081’s
actual performance. However, if a guard ring is held within
5 mV of the inputs, then even a resistance of 10
11
would
cause only 0.05 pA of leakage current. See Figure 5 for typi-
cal connections of guard rings for standard op-amp
configurations.
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
See Figure 6
up-in-the-air
wiring.
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-
DS011423-6
FIGURE 4. Example of Guard Ring in P.C. Board
Layout
DS011423-7
Inverting Amplifier
DS011423-8
Non-Inverting Amplifier
DS011423-9
Follower
FIGURE 5. Typical Connections of Guard Rings
DS011423-10
(Input pins are lifted out of PC board and soldered directly to components.
FIGURE 6. Air Wiring
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