lmc6464amj-qml

Manufacturer Part Numberlmc6464amj-qml
DescriptionLmc6464qml Quad Micropower, Rail-to-rail Input And Output Cmos Operational Amplifier
ManufacturerNational Semiconductor Corporation
lmc6464amj-qml datasheet
 
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Application Information
1.0 INPUT COMMON-MODE VOLTAGE RANGE
The LMC6464 has a rail-to-rail input common-mode voltage
range.
Figure 1
shows an input voltage exceeding both sup-
plies with no resulting phase inversion on the output.
FIGURE 1. An Input Voltage Signal Exceeds
the LMC6464 Power Supply Voltage
with No Output Phase Inversion
The absolute maximum input voltage at V
beyond either supply rail at room temperature. Voltages
greatly exceeding this absolute maximum rating, as in
2, can cause excessive current to flow in or out of the input
pins, possibly affecting reliability. The input current can be
externally limited to ±5 mA, with an input resistor, as shown
in
Figure
3.
FIGURE 2. A ±7.5V Input Signal Greatly Exceeds
the 3V Supply in
Figure 3
No Phase Inversion Due to R
FIGURE 3. Input Current Protection for Voltages
Exceeding the Supply Voltage
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2.0 RAIL-TO-RAIL OUTPUT
The approximated output resistance of the LMC6464 is
180Ω sourcing, and 130Ω sinking at V
sourcing and 83Ω sinking at V
swing can be estimated as a function of load using the cal-
culated output resistance.
3.0 CAPACITIVE LOAD TOLERANCE
The LMC6464 can typically drive a 200 pF load with V
at unity gain without oscillating. The unity gain follower is the
most sensitive configuration to capacitive load. Direct capac-
itive loading reduces the phase margin of op-amps. The
combination of the op-amp's output impedance and the ca-
pacitive load induces phase lag. This results in either an
underdamped pulse response or oscillation.
Capacitive load compensation can be accomplished using
resistive isolation as shown in
component of the load in parallel to the capacitive component,
the isolation resistor and the resistive load create a voltage
divider at the output. This introduces a DC error at the output.
20160605
+
= 3V is 300 mV
Figure
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FIGURE 5. Pulse Response of the LMC6464
Causing
Figure 5
displays the pulse response of the LMC6464 circuit
I
in
Figure
4.
Another circuit, shown in
drive capacitive loads. This circuit is an improvement to the
circuit shown in
well as AC stability. R1 and C1 serve to counteract the loss
of phase margin by feeding the high frequency component of
the output signal back to the amplifiers inverting input, thereby
preserving phase margin in the overall feedback loop. The
20160607
values of R1 and C1 should be experimentally determined by
the system designer for the desired pulse response. In-
creased capacitive drive is possible by increasing the value
of the capacitor in the feedback loop.
12
= 3V, and 110Ω
S
= 5V. The maximum output
S
Figure
4. If there is a resistive
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FIGURE 4. Resistive Isolation of
a 300 pF Capacitive Load
20160609
Circuit Shown in
Figure 4
Figure
6, is also used to indirectly
Figure 4
because it provides DC accuracy as
= 5V
S