Dear Team,
I have a bootstrapped opamp circuit as shown below.It has 3 opamps.
If I want to check the stability of this circuit may I know where I need to break the loop and apply the stimulus?
Regards
HARI
Hari,
Before you may conduct any stability analysis, you must make sure that the circuit operates linearly. However, it is clear that your bootstrapped op amp, with VF2=VF3=30V (LMC662A has zero supply voltage) and VM1=VM2=~0.7V (should be Vos<5mV), does not work properly - see below. You need to fix the circuit before any stability analysis may be performed.
Hi Marek,
I think the issue is with the spice model of OPA455.
I changed opa455 to OPA462. Now I am getting voltages as expected. Please see the below image.
I am also sending the TINA file . Now you can help me with stability analysis.
Regards
HARI
Hari,
With 64 degrees phase margin, the circuit is very stable (minimum recommended 45 degrees) - see below.
You may confirm circuit stability by running a small-signal transient analysis (overshoot of 7% vs max recommended of 25%) - see below.
Below please see attached Tina-TI files.
Hari,
Yes, you do need to break the loop to check the stability of OPA462 op amps especially since they drive a large 4.7nF load.
As you may see below, the op amps have only 4.8 degrees phase margin while the minimum recommended is 45 degrees.
Adding 100ohm in series with 4.7nF increases the phase margin to 70 degrees - see below.
