TINA/Spice/OPA1611: Phase Margin

Hi Sadanori,

I would do it this way:

I would remove C4 and R7:

sadanori.TSC

See also this link:

training.ti.com/ti-precision-labs-op-amps-stability-6

Kai

Hi Kato,
The model for the OPA1611 does model open loop gain and phase and output impedance of the OPA1611.

In your design, the phase shift at Vout does not represent the phase margin of the circuit. You should instead measure the phase where feedback returns to the amplifier (the junction of R7, R5, L1, and C8), as Kai's post shows.

Also, keep in mind that by breaking the feedback loop with L1, the input capacitance of the OPA1611 will no longer impact your circuit, so the input capacitors will need to be modeled externally as Kai has done with C3 and C5 in his schematic.

More information on stability analysis, including techniques to address stability concerns, can be found in our TI Precision Labs series on Stability, the first video of which can be found here: training.ti.com/ti-precision-labs-op-amps-stability-1