# Question about an op amp

## Main Question or Discussion Point

For the INA101, in the configuration for the most basic circuit with the TO-100 package, two 1 mircofarad capacitors seem to be required to be placed in parallel with the supply voltages. Why is this, and is it actually necessary for an operating circuit, since the circuit example with the Dip package has no such requirement? You can see what I am talking about on pg. 6 in the linked pdf.
http://www.chem.duke.edu/~boris/datasheets/INA101.pdf" [Broken]

Thanks,
-Scott

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George Jones
Staff Emeritus
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For the INA101, in the configuration for the most basic circuit with the TO-100 package, two 1 mircofarad capacitors seem to be required to be placed in parallel with the supply voltages. Why is this, and is it actually necessary for an operating circuit, since the circuit example with the Dip package has no such requirement? You can see what I am talking about on pg. 6 in the linked pdf.
http://www.chem.duke.edu/~boris/datasheets/INA101.pdf" [Broken]

Thanks,
-Scott
They provide paths to ground for (possible) crap riding on the power supply voltages.

Look at the second sentence under APPLICATION INFORMATION.

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-Scott

berkeman
Mentor
They provide paths to ground for (possible) crap riding on the power supply voltages.

Look at the second sentence under APPLICATION INFORMATION.
And in general, decoupling power supply input pins is good practice, both for analog and digital devices.

The bypass capacitors also help to keep the demons of oscillation at bay...

Hey another quick question, for the power supply voltage, how close to +/-15 volts do I need to be to have the instrument work right? Is it correct that the op amp will work w/ a +/-5 volt to a +/-20 volt supply?

Thanks,
-Scott

The datasheet states that the minimum supply voltage is +/-5V and the maximum supply voltage is +/- 20V.

Therefore, you may assume that the device will operate within its stated parameters over that range of supply voltages.

Interestingly (?) enough, the Absolute Max supply voltage is +/-20V too, which would appear to be sailing a bit close to the wind... I suppose it depends on how absolute that max is.

berkeman
Mentor
Keep in mind that not many opamps will let you take the inputs to the rails, and not many will be able to drive their outputs to the rails. Look in the datasheet for the specifications for how close the inputs and outputs can go to the rails, and keep that limitation in mind in your design.