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AP358

LOW POWER DUAL OPERATIONAL AMPLIFIERS

Diodes Incorporated. 

AP358

LOW POWER DUAL OPERATIONAL AMPLIFIERS

Application Information

The AP358 series are 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

0 VDC. 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 VDC.

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 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 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 larger load capacitance must be driven by the

amplifier.

The bias network of the AP358 establishes a drain current

which is independent of the magnitude of the power supply

voltage over the range of 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

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.

AP358 Rev. 4

12 of 15

www.diodes.com

OCTOBER 2006

© Diodes Incorporated

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