Typical Performance Curves

(Continued)

Current Limiting

00856233

Application Hints

The LP324 series is a micro-power pin-for-pin equivalent to

the LM324 op amps. Power supply current, input bias cur-

rent, and input offset current have all been reduced by a

factor of 10 over the LM324. Like its predecessor, the LP324

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

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 accommo-

dated and, as input differential voltage protection diodes are

not needed, no large input currents result from large differ-

ential 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

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 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.

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.

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-

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.

Driving CMOS

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