• State Resolved
  • Locked Locked
  • Replies 1 reply
  • Subscribers 47 subscribers
  • Views 550 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

Opamp stability

HARSHIT MISHRA
Prodigy 25 points

Hello everyone,

I was going through your opamp stability videos by Tim Green,Collin Wells,Art Kay and Ian Williams. While explaining Riso + dual feedback compensation, it mentions a range of CF values as   (6*Riso*Cload / RF) < CF < (10*Riso*Cload / RF) and RF >=100*Riso.

Can anyone please explain me, how does it come ?

The link for the same is https://training.ti.com/ti-precision-labs-op-amps-stability-6?cu=14685

  • 0
    TI__Guru 64775 points

    Hi Harshit,


     As mentioned in the videos the RF value is selected such that it’s substantially larger than Riso which prevents interactions between Riso and RF allowing for some simplifications of the equations that bound the circuit.  The CF value is selected such that the feedback path formed through CF dominates the response before the interaction of Riso and Cload begins to negatively affect the feedback path through RF.  Therefore we want the frequency  of 1/(2*pi*RF*CF) to be a much lower frequency than the 1/(2*pi*Riso*Cload) combination.  Rearranging the circuit, solving for CF, and then adding some margin yields the equations in the videos.