Why do some op amps require capacitors in parallel with supply voltages?

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Discussion Overview

The discussion centers on the necessity of using capacitors in parallel with supply voltages for the INA101 operational amplifier, particularly in the context of different package configurations. Participants explore the implications of this requirement for circuit functionality and performance.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • Some participants note that capacitors provide paths to ground for noise on the power supply voltages, suggesting their importance in circuit stability.
  • Others argue that decoupling power supply input pins is generally good practice for both analog and digital devices.
  • One participant mentions that bypass capacitors help mitigate oscillation issues.
  • A question is raised regarding the acceptable range of supply voltages for the INA101, with references to the datasheet stating a minimum of +/-5V and a maximum of +/-20V.
  • Another participant highlights that many op-amps do not allow inputs or outputs to reach the supply rails, indicating a need to consult the datasheet for specific limitations.

Areas of Agreement / Disagreement

Participants express differing views on the necessity and implications of using capacitors with the INA101. While some support their use for stability and noise reduction, others question the necessity based on different package configurations. The discussion remains unresolved regarding the absolute necessity of these capacitors in all configurations.

Contextual Notes

Participants reference the datasheet for the INA101, indicating that the operational parameters and limitations may vary based on specific configurations and applications. There is an acknowledgment of potential ambiguities in the maximum supply voltage specifications.

scott_alexsk
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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"

Thanks,
-Scott
 
Last edited by a moderator:
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scott_alexsk said:
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"

Thanks,
-Scott

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

Look at the second sentence under APPLICATION INFORMATION.
 
Last edited by a moderator:
Sorry about that.

Thanks for the quick reply.
-Scott
 
George Jones said:
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.
 
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.
 

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