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Application Summary

The GS321 op amp can operate with a single or dual power supply voltage, has true-differential inputs,

and remain in the linear mode with an input common-mode voltage of 0 VDC. This amplifier operates

over a wide range of power supply voltages, with little change in performance characteristics. At 25°C

amplifier operation is possible down to a minimum supply voltage of 3V.

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 VDC (at 25°C). An input

clamp diode with a resistor to the IC input terminal can be used.

To reduce the power supply drain, the amplifier has 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 to

reduce 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 large load capacitance must be driven by the

amplifier.

The bias network of the GS321 establishes a supply current which is independent of the magnitude of

the power supply voltage over the range of from 3 VDC to 30 VDC.

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. The larger value of output source current which is available at 25°C provides a larger

output current capability at elevated temperatures 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.