SNOSBX6C – SEPTEMBER 1999 – REVISED MARCH 2013
Typical Performance Curves (continued)
Current Limiting
Figure 15.
APPLICATION HINTS
The LP324-N series is a micro-power pin-for-pin equivalent to the LM324 op amps. Power supply current, input
bias current, and input offset current have all been reduced by a factor of 10 over the LM324. Like its
predecessor, the LP324-N series op amps can operate on single supply, have true-differential inputs, and remain
in the linear mode with an input common-mode voltage of 0 V
DC
.
The pinouts of the package have been designed to simplify PC board layouts. Inverting inputs are adjacent to
outputs for all of the amplifiers and the outputs have also been placed at the corners of the package (pins 1, 7, 8,
and 14).
Precautions should be taken to insure that the power supply for the integrated circuit never becomes reversed in
polarity or the unit is not inadvertently installed backwards in the test socket as an unlimited current surge
through the resulting forward diode within the IC could destroy the unit.
Large differential input voltages can be easily accommodated and, as input differential voltage protection diodes
are not needed, no large input currents result from large differential input voltages. The differential input voltage
may be larger than V
+
without damaging the device. Protection should be provided to prevent the input voltages
from going negative more than
−0.3
V
DC
(at 25°C). An input clamp diode with a resistor to the IC input terminal
can be used.
The amplifiers have a class B output stage which allows the amplifiers to both source and sink output currents. In
applications where crossover distortion is undesirable, a resistor should be used from the output of the amplifier
to ground. The resistor biases the output into class A operation.
The LP324-N has improved stability margin for driving capacitive loads. No special precautions are needed to
drive loads in the 50 pF to 1000 pF range. It should be noted however that since the power supply current has
been reduced by a factor of 10, so also has the slew rate and gain bandwidth product. This reduction can cause
reduced performance in AC applications where the LM324 is being replaced by an LP324-N. Such situations
usually occur when the LM324 has been operated near its power bandwidth.
Output short circuits either to ground or to the positive power supply should be of short time duration. Units can
be destroyed, not as a result of the short circuit current causing metal fusing, but rather due to the large increase
in IC chip dissipation which will cause eventual failure due to excessive junction temperatures. For example: If all
four amplifiers were simultaneously shorted to ground on a 10V supply the junction temperature would rise by
110°C.
Exceeding the negative common-mode limit on either input will cause a reversal of phase to the output and force
the amplifier to the corresponding high or low state. Exceeding the negative common-mode limit on both inputs
will force the amplifier output to a high state. Exceeding the positive common-mode limit on a single input will not
change the phase of the output. However, if both inputs exceed the limit, the output of the amplifier will be forced
to a low state. In neither case does a latch occur since returning the input within the common mode range puts
the input stage and thus the amplifier in a normal operating mode.
6
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