OPA2197: Input protection for open circuits

Hi Jaynie, 

Jaynie Shorb said:

Do you expect random voltage outputs given an open input or should it settle to a known dc value?

Yes. The op amp's input is high impedance, and it should not configured as a floating point. If input is floating, output will be undetermined and float as well, may cap to a saturated state either cap to Vcc or Vee. 

In many high impedance bench grade multimeter, the input lead should not be left in open, otherwise it will display whatever figures from the floating input - same observation. 

In Tina or other simulator, the system has to converge into a defined state, otherwise the tool will prompt an error if a simulation is unable to converge. 

Here is an application note why one has to terminate unused op amp properly in a design. 

https://www.ti.com/lit/ab/sboa204a/sboa204a.pdf?ts=1742598450962&ref_url=https%253A%252F%252Fwww.google.com%252F

https://e2e.ti.com/blogs_/archives/b/thesignal/posts/the-unused-op-amp-what-to-do

Regarding op amp's input protections, we have op amps have input-overvoltage protection, such as OPA2206, see the link below. 

https://e2e.ti.com/blogs_/archives/b/thesignal/posts/the-unused-op-amp-what-to-do

Regarding an op amp's output overvoltage and overcurrent protection, the implementation depends on the design requirements. If the output overvoltage and overcurrent are exceeding the op amp's absolute maximum ratings, you may implement the following scheme to protect op amp's output.  

If you have other questions, please let me know. 

Best,

Raymond