Application Discussion
Introduction
Typical Performance plots are valid for both devices
under the specified conditions. Generally, lowering Rf
from its recommended value will peak the frequency
response and extend the bandwidth while increasing its
value will roll off the response. Reducing the value of Rf
toofarbelowitsrecommendedvaluewillcauseovershoot,
ringing and eventually oscillation. For more information
see Application Note OA-20 and OA-13.
TheCLC431andtheCLC432aredualwidebandcurrent-
feedback op amps that operate from single (+10V to
+33V) or dual (±5V to ±16.5) power supplies. The
CLC431 is equipped with a disable feature and is offered
in 14-pin DIP and SOIC packages. The CLC432 is
packaged in a standard 8-pin dual pinout and is offered
inan8-pinDIPandSOIC.Evaluationboardsareavailable
for each version of both devices. The evaluation boards
canassistinthedeviceand/orapplicationevaluationand
were used to generate the typical device performance
plots on the preceding pages.
In order to optimize the devices' frequency and phase
response for gains other than +2V/V it is recommended
to adjust the value of the feedback resistor. The two plots
found in the Typical Performance section entitled
"Recommended Rf vs. Gain" provide the means of
selecting the feedback-resistor value that optimizes
frequency and phase response over the CLC431/
CLC432's gain range. Both plots show the value of Rf
approaching a nonzero minimum at high non-inverting
gains, which is characteristic of current-feedback op
amps and yields best results. The linear portion of the
twoRf vs. Inverting-gaincurvesresultsfromthelimitation
placed on Rg (i.e. Rg ≥ 50Ω) in order to maintain an
adequateinputimpedancefortheinvertingconfiguration.
It should be noted that for stable operation a non-
inverting gain of +1 requires an Rf equal to 1kΩ for both
the CLC431 and the CLC432.
Each of the CLC431/CLC432's dual channels provide
closely matched DC & AC electrical performance
characteristics making them ideal choices for wideband
signal processing. The CLC431, with its disable feature,
can easily be configured as a 2:1 mux or several can be
usedtoforma10:1muxwithoutperformancedegradation.
Thetwoclosely-matchedchannelsoftheCLC432canbe
combinedtoformcompositecircuitsforsuchapplications
as filter blocks, integrators, transimpedance amplifiers
and differential line drivers and receivers.
Feedback Resistor Selection
The loop gain and frequency response for a current-
feedback operational amplifier is determined largely by
the feedback resistor (Rf). Package parasitics also
influence ac response. Since the package parasitics of
the CLC431 and the CLC432 are different, the optimum
frequencyandphaseresponsesareobtainedwithdifferent
valuesoffeedbackresistor(forAV=+2;CLC431:Rf=866Ω,
CLC432: Rf=750Ω). The Electrical Characteristics and
CLC431 Disable Feature
The CLC431 disable feature can be operated either
single-endedlyordifferentiallytherebyaccommodatinga
wide range of logic families. There are three pins asso-
ciated with the disable feature of each of the CLC431's
two amplifiers:
(please see pinout on
DIS,DIS and VRTTL
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