Application Hints
(Continued)
The amplifiers have a class B output stage which allows the
amplifiers to both source and sink output currents. In appli-
cations 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 has improved stability margin for driving capaci-
tive 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. 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 de-
stroyed, 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 exces-
sive 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.
Driving CMOS
Exceeding the negative common-mode limit on either input
will cause a reversal of phase to the output and force the am-
plifier 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 nei-
ther 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.
The circuits presented in the section on typical applications
emphasize operation on only a single power supply voltage.
If complementary power supplies are available, all of the
standard op amp circuits can be used. In general, introduc-
ing a pseudo-ground (a bias voltage reference to V
+
/2) will
allow operation above and below this value in single power
supply systems. Many application circuits are shown which
take advantage of the wide input common-mode voltage
range which includes ground. In most cases, input biasing is
not required and input voltages which range to ground can
easily be accommodated.
Comparator with Hysteresis
DS008562-3
DS008562-6
Non-Inverting Amplifier
Adder/Subtractor
DS008562-4
DS008562-7
Unity Gain Buffer
Positive Integrator
DS008562-5
DS008562-8
5
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