lmc6464amj-qml National Semiconductor Corporation, lmc6464amj-qml Datasheet - Page 12

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

www.national.com
Application Information
1.0 INPUT COMMON-MODE VOLTAGE RANGE
The LMC6464 has a rail-to-rail input common-mode voltage
range.
plies with no resulting phase inversion on the output.
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
FIGURE 2. A ±7.5V Input Signal Greatly Exceeds
FIGURE 3. Input Current Protection for Voltages
FIGURE 1. An Input Voltage Signal Exceeds
Figure 1
3.
the LMC6464 Power Supply Voltage
the 3V Supply in
with No Output Phase Inversion
Exceeding the Supply Voltage
No Phase Inversion Due to R
shows an input voltage exceeding both sup-
Figure 3
Causing
+
= 3V is 300 mV
20160607
I
20160605
20160606
Figure
12
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.
Figure 5
in
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
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.
Figure
FIGURE 5. Pulse Response of the LMC6464
displays the pulse response of the LMC6464 circuit
4.
FIGURE 4. Resistive Isolation of
Figure 4
a 300 pF Capacitive Load
Circuit Shown in
because it provides DC accuracy as
Figure
Figure
S
= 5V. The maximum output
6, is also used to indirectly
Figure 4
4. If there is a resistive
S
= 3V, and 110Ω
20160608
20160609
S
= 5V