LM358N/D
APPLICATION HINTS
The
LM358
is op amps which 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 0V. 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
minimu m supply voltage of 2.3 V.
Precautions should be taken to insure that the power supply for the integrated circuit
never becomes reversed in polarity or that th e 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 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 -0.3V (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. Wh ere 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 accomodated using the worst-case non-inverting
unity gain connection. Large closed loop gains or resistive isolation should be used if larger
load capacitance must be driven by the amplifier.
Output short circuits either to ground or to the positive power suppl y 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 larg er value of output source current which is
available at 25°C provides a larger output curre nt capability at elevated temperatures (see
typical performance characteristics) than a standard IC op amp.
6/8
TGS [ Tiger Electronic Co.,Ltd ]
