LMC7101AIM5X National Semiconductor, LMC7101AIM5X Datasheet - Page 18

• Manufacturer Part Number: LMC7101AIM5X
• Description: IC,Operational Amplifier,SINGLE,CMOS,TSOP,5PIN,PLASTIC
• Manufacturer: National Semiconductor

Specifications of LMC7101AIM5X

• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

www.national.com
Application Information
4.0 CAPACITIVE LOAD TOLERANCE
The LMC7101 can typically directly drive a 100 pF load with
V
follower is the most sensitive configuration. Direct capacitive
loading reduces the phase margin of op-amps. The combi-
nation of the op-amp’s output impedance and the capacitive
load induces phase lag. This results in either an under-
damped pulse response or oscillation.
Capacitive load compensation can be accomplished using
resistive isolation as shown in Figure 4. This simple tech-
nique is useful for isolating the capacitive input of multiplex-
ers and A/D converters.
S
= 15V at unity gain without oscillating. The unity gain
FIGURE 4. Resistive Isolation
of a 330 pF Capacitive Load
01199111
(Continued)
18
5.0 COMPENSATING FOR INPUT CAPACITANCE WHEN
USING LARGE VALUE FEEDBACK RESISTORS
When using very large value feedback resistors, (usually
>
input capacitance due to transducers, photodiodes, and cir-
cuit 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 5), C
which typically provides significant overcompensation.
Printed circuit board stray capacitance may be larger or
smaller than that of a breadboard, so the actual optimum
value for C
checked on the actual circuit. (Refer to the LMC660 quad
CMOS amplifier data sheet for a more detailed discussion.)
FIGURE 5. Cancelling the Effect of Input Capacitance
500 kΩ) the large feed back resistance can react with the
F
f
may be different. The values of C
is first estimated by:
R
1
C
IN
or
≤ R
2
C
f
F
should be
01199112