lmc6034-mda National Semiconductor Corporation, lmc6034-mda Datasheet - Page 6

• Manufacturer Part Number: lmc6034-mda
• Description: Cmos Quad Operational Amplifier
• Manufacturer: National Semiconductor Corporation

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Typical Performance Characteristics
Note: Avoid resistive loads of less than 500Ω, as they may cause
instability.
Applications Hint
Amplifier Topolgy
The topology chosen for the LMC6034, shown in Figure 1, is
unconventional (compared to general-purpose op amps) in
that the traditional unity-gain buffer output stage is not used;
instead, the output is taken directly from the output of the
integrator, to allow a larger output swing. Since the buffer
traditionally delivers the power to the load, while maintaining
high op amp gain and stability, and must withstand shorts to
either rail, these tasks now fall to the integrator.
As a result of these demands, the integrator is a compound
affair with an embedded gain stage that is doubly fed forward
(via C
driver. In addition, the output portion of the integrator is a
push-pull configuration for delivering heavy loads. While
sinking current the whole amplifier path consists of three
gain stages with one stage fed forward, whereas while
sourcing the path contains four gain stages with two fed
forward.
f
and Cff) by a dedicated unity-gain compensation
Non-Inverting Large Signal
Capacitive Load
Pulse Response
Stability vs
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V
6
S
=
The large signal voltage gain while sourcing is comparable
to traditional bipolar op amps, even with a 600Ω load. The
gain while sinking is higher than most CMOS op amps, due
to the additional gain stage; however, under heavy load
(600Ω) the gain will be reduced as indicated in the Electrical
Characteristics.
Compensating Input Capacitance
The high input resistance of the LMC6034 op amps allows
the use of large feedback and source resistor values without
losing gain accuracy due to loading. However, the circuit will
be especially sensitive to its layout when these large-value
resistors are used.
Every amplifier has some capacitance between each input
and AC ground, and also some differential capacitance be-
tween the inputs. When the feedback network around an
amplifier is resistive, this input capacitance (along with any
additional capacitance due to circuit board traces, the
socket, etc.) and the feedback resistors create a pole in the
feedback path. In the following General Operational Amplifier
circuit, Figure 2 the frequency of this pole is
where C
including amplifier input capcitance and any stray capaci-
tance from the IC socket (if one is used), circuit board traces,
±
FIGURE 1. LMC6034 Circuit Topology (Each Amplifier)
7.5V, T
S
A
= 25˚C unless otherwise specified (Continued)
is the total capacitance at the inverting input,
Capacitive Load
Stability vs
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01113403