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參數資料
| 型號： | LMC662EM |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 運算放大器 |
| 英文描述： | CMOS Dual Operational Amplifier |
| 中文描述： | DUAL OP-AMP, 6500 uV OFFSET-MAX, 1.4 MHz BAND WIDTH, PDSO8 |
| 封裝： | SO-8 |
| 文件頁數： | 7/13頁 |
| 文件大?。?/td> | 430K |
| 代理商： | LMC662EM |
Application Hints
(Continued)
margin
lower-frequency circuit operation. Thus, larger values of ca-
pacitance can be tolerated without oscillation. Note that in all
cases, the output will ring heavily when the load capacitance
is near the threshold for oscillation.
to
a
safe
value
without
interfering
with
Capacitive load driving capability is enhanced by using a pull
up resistor to V
+
Figure 4 Typically a pull up resistor con-
ducting 500 μA or more will significantly improve capacitive
load responses. The value of the pull up resistor must be de-
termined based on the current sinking capability of the ampli-
fier with respect to the desired output swing. Open loop gain
of the amplifier can also be affected by the pull up resistor
(see Electrical Characteristics).
PRINTED-CIRCUIT-BOARD LAYOUT
FOR HIGH-IMPEDANCE WORK
It is generally recognized that any circuit which must operate
with less than 1000 pA of leakage current requires special
layout of the PC board. When one wishes to take advantage
of the ultra-low bias current of the LMC662, typically less
than 0.04 pA, it is essential to have an excellent layout. For-
tunately, the techniques for obtaining low leakages are quite
simple. First, the user must not ignore the surface leakage of
the PC board, even though it may sometimes appear accept-
ably low, because under conditions of high humidity or dust
or contamination, the surface leakage will be appreciable.
To minimize the effect of any surface leakage, lay out a ring
of foil completely surrounding the LMC662’s inputs and the
terminals of capacitors, diodes, conductors, resistors, relay
terminals, etc. connected to the op-amp’s inputs. See Figure
5 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 an input. This
would cause a 100 times degradation from the LMC662’s ac-
tual 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, or perhaps a minor
(2:1) degradation of the amplifier’s performance. See Fig-
ures 6, 7, 8 for typical connections of guard rings for stan-
dard op-amp configurations. If both inputs are active and at
high impedance, the guard can be tied to ground and still
provide some protection; see Figure 9
DS009763-5
FIGURE 3. Rx, Cx Improve Capacitive Load Tolerance
DS009763-23
FIGURE 4. Compensating for Large Capacitive Loads
with a Pull Up Resistor
DS009763-16
FIGURE 5. Example, using the LMC660,
of Guard Ring in P.C. Board Layout
DS009763-17
FIGURE 6. Guard Ring Connections: Inverting
Amplifier
DS009763-18
FIGURE 7. Guard Ring Connections: Non-Inverting
Amplifier
DS009763-19
FIGURE 8. Guard Ring Connections: Follower
www.national.com
7
相關PDF資料 |
PDF描述 |
|---|---|
| LMC662EN | CMOS Dual Operational Amplifier |
| LMC662 | CMOS Dual Operational Amplifier |
| LMC6681 | Low Voltage, Rail-To-Rail Input and Output CMOS |
| LMC6681AIM | Low Voltage, Rail-To-Rail Input and Output CMOS |
| LMC6681AIMX | Low Voltage, Rail-To-Rail Input and Output CMOS |
相關代理商/技術參數 |
參數描述 |
|---|---|
| LMC662EN | 制造商:Rochester Electronics LLC 功能描述:- Bulk 制造商:Texas Instruments 功能描述: |
| LMC6681 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Low Voltage, Rail-To-Rail Input and Output CMOS |
| LMC6681AIM | 制造商:Rochester Electronics LLC 功能描述:- Bulk 制造商:Texas Instruments 功能描述: |
| LMC6681AIMX | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Low Voltage, Rail-To-Rail Input and Output CMOS |
| LMC6681AIN | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Low Voltage, Rail-To-Rail Input and Output CMOS |
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