lmc6464amj-qml National Semiconductor Corporation, lmc6464amj-qml Datasheet - Page 13

• Manufacturer Part Number: lmc6464amj-qml
• Description: Lmc6464qml Quad Micropower, Rail-to-rail Input And Output Cmos Operational Amplifier
• Manufacturer: National Semiconductor Corporation

The pulse response of the circuit shown in
in
4.0 COMPENSATING FOR INPUT CAPACITANCE
It is quite common to use large values of feedback resistance
with amplifiers that have ultra-low input current, like the
LMC6464. Large feedback resistors can react with small val-
ues of input capacitance due to transducers, photodiodes,
and circuits board parasitics to reduce phase margins.
The effect of input capacitance can be compensated for by
adding a feedback capacitor. The feedback capacitor (as in
Figure 8
FIGURE 8. Canceling the Effect of Input Capacitance
Figure
FIGURE 6. LMC6464 Non-Inverting Amplifier,
Compensated to Handle a 300 pF Capacitive
), C
7.
F
, is first estimated by:
FIGURE 7. Pulse Response of
LMC6464 Circuit in
and 100 KΩ Resistive Load
Figure 6
Figure 6
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is shown
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13
or
which typically provides significant overcompensation.
Printed circuit board stray capacitance may be larger or small-
er than that of a breadboard, so the actual optimum value for
C
the actual circuit. (Refer to the LMC660 quad CMOS amplifier
data sheet for a more detailed discussion.)
5.0 OFFSET VOLTAGE ADJUSTMENT
Offset voltage adjustment circuits are illustrated in
and
are used to reduce power consumption while providing typi-
cally ±2.5 mV of adjustment range, referred to the input, for
both configurations with V
6.0 SPICE MACROMODEL
A Spice macromodel is available for the LMC6464. This mod-
el includes a simulation of:
•
•
•
•
•
and many more characteristics as listed on the macromodel
disk.
Contact the National Semiconductor Customer Response
Center to obtain an operational amplifier Spice model library
disk.
F
may be different. The values of C
Input common-mode voltage range
Frequency and transient response
GBW dependence on loading conditions
Quiescent and dynamic supply current
Output swing dependence on loading conditions
Figure
FIGURE 10. Non-Inverting Configuration
10. Large value resistances and potentiometers
FIGURE 9. Inverting Configuration
Offset Voltage Adjustment
Offset Voltage Adjustment
R
1
S
C
= ±5V.
I
≤
R
2
C
F
F
should be checked on
www.national.com
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Figure 9
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