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參數(shù)資料
| 型號： | LF453CM |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 運動控制電子 |
| 英文描述： | LF453 Wide-Bandwidth Dual JFET-Input Operational Amplifiers |
| 中文描述： | DUAL OP-AMP, 5000 uV OFFSET-MAX, 4 MHz BAND WIDTH, PDSO8 |
| 封裝： | 0.150 INCH, PLASTIC, SOP-8 |
| 文件頁數(shù)： | 6/8頁 |
| 文件大?。?/td> | 219K |
| 代理商： | LF453CM |
Application Hints
These devices are op amps with an internally trimmed input
offset voltage and JFET input devices (BI-FET II). These
JFETs have large reverse breakdown voltages from gate to
source and drain eliminating the need for clamps across the
inputs. Therefore, large differential input voltages can easily
be accommodated without a large increase in input current.
The maximum differential input voltage is independent of
the supply voltages. However, neither of the input voltages
should be allowed to exceed the negative supply as this will
cause large currents to flow which can result in a destroyed
unit.
Exceeding the negative common-mode limit with the non-in-
verting input, or with both inputs, will force the output to a
high state, potentially causing a reversal of phase to the
output. In neither case does a latch occur since raising the
input back within the common-mode range again puts the
input stage and thus the amplifier in a normal operating
mode.
Exceeding the positive common-mode limit on a single input
will not change the phase of the output; however, if both
inputs exceed the limit, the output of the amplifier will be
forced to a high state.
The amplifiers will operate with a common-mode input volt-
age equal to the positive supply; however, the gain band-
width and slew rate may be decreased in this condition.
When the negative common-mode voltage swings to within
3V of the negative supply, an increase in input offset voltage
may occur.
Each amplifier is individually biased by a zener reference
which allows normal circuit operation on
g
5V power sup-
plies. Supply voltages less than these may result in lower
gain bandwidth and slew rate.
The amplifiers will drive a 2 k
X
load resistance to
g
10V
over the full temperature range of 0
§
C to
a
70
§
C. If the am-
plifier is forced to drive heavier load currents, however, an
increase in input offset voltage may occur on the negative
voltage swing and finally reach an active current limit on
both positive and negative swings.
Precautions should be taken to ensure that the power sup-
ply for the integrated circuit never becomes reversed in po-
larity or that the unit is not inadvertently installed backwards
in a socket as an unlimited current surge through the result-
ing forward diode within the IC could cause fusing of the
internal conductors and result in a destroyed unit.
As with most amplifiers, care should be taken with lead
dress, component placement and supply decoupling in or-
der to ensure stability. For example, resistors from the out-
put to an input should be placed with the body close to the
input to minimize ‘‘pick-up’’ and maximize the frequency of
the feedback pole by minimizing the capacitance from the
input to ground.
A feedback pole is created when the feedback around any
amplifier is resistive.The parallel resistance and capacitance
from the input of the device (usually the inverting input) to
AC ground set the frequency of the pole. In many instances
the frequency of this pole is much greater than the expected
3 dB frequency of the closed loop gain and consequently
there is negligible effect on stability margin. However, if the
feedback pole is less than approximately 6 times the ex-
pected 3 dB frequency a lead capacitor should be placed
from the output to the input of the op amp. The value of the
added capacitor should be such that the RC time constant
of this capacitor and the resistance it parallels is greater
than or equal to the original feedback pole time constant.
The benefit of the SO package results from its very small
size. It follows, however, that the die inside the SO package
is less protected from external physical forces than a die in
a standard DIP would be, because there is so much less
plastic in the SO. Therefore, not following certain precau-
tions when board mounting the LF453CM can put mechani-
cal stress on the die, lead frame, and/or bond wires. This
can cause shifts in the LF453CM’s parameters, even caus-
ing them to exceed limits specified in the Electrical Charac-
teristics. For recommended practices in LF453CM surface
mounting refer to Application Note AN450 ‘‘Surface Mount-
ing Methods and Their Effect on Product Reliability’’ and to
the section titled ‘‘Surface Mount’’ found in any Rev 1. Lin-
ear Databook volume.
6
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