Diodes LM358 - Manual (Page 12)

LM358
LOW POWER DUAL OPERATIONAL AMPLIFIERS
LM358
Document number: DS35167 Rev. 2 - 2
12 of 14
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February 2011
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Application Information
The LM358 series are op amps operate with only a single
power supply voltage, have true-differential inputs, and
remain in the linear mode with an input common-mode
voltage of 0 V
DC
. These amplifiers operate over a wide
range of power supply voltage with little change in
performance characteristics. At 25°C amplifier operation
is possible down to a minimum supply voltage of 2.3 V
DC
.
Precautions should be taken to insure that the power
supply for the integrated circuit never becomes reversed
in polarity or that the unit is not inadvertently installed
backwards in a test socket as an unlimited current surge
through the resulting forward diode within the IC could
cause fusing of the internal conductors and result in a
destroyed unit.
Large differential input voltages can be easily
accommodated and, as input differential voltage
protection diodes are not needed, no large input currents
result. 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.
To reduce the power supply current drain, the amplifiers
have a class A output stage for small signal levels which
converts to class B in a large signal mode. This allows
the amplifiers to both source and sink large output
currents. Therefore both NPN and PNP external current
boost transistors can be used to extend the power
capability of the basic amplifiers. The output voltage
needs to raise approximately 1 diode drop above ground
to bias the on-chip vertical PNP transistor for output
current sinking applications.
For AC applications, where the load is capacitively
coupled to the output of the amplifier, a resistor should
be used, from the output of the amplifier to ground to
increase the class A bias current and prevent crossover
distortion. Where the load is directly coupled, as in
DC applications, there is no crossover distortion.
Capacitive loads which are applied directly to the output
of the amplifier reduce the loop stability margin. Values of
50pF can be accommodated using the worst-case non-
inverting unity gain connection. Large closed loop gains
or resistive isolation should be used if a larger load
capacitance must be driven by the amplifier.
The bias network of the LM358 establishes a drain
current which is independent of the magnitude of the
power supply voltage over the range of 3 V
DC
to 30 V
DC
.
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 function temperatures. Putting direct
short-circuits on more than one amplifier at a time will
increase the total IC power dissipation to destructive
levels, if not properly protected with external dissipation
limiting resistors in series with the output leads of the
amplifiers. The larger value of output source current
which is available at 25°C provides a larger output
current capability at elevated temperatures (see typical
performance characteristics) than a standard IC op amp.
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, introducing a pseudo-ground (a bias
voltage reference of 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.