Tying to fine-tune a simple amplifier based on on OPA387 I found out that the higher Riso resistor value the lower the stability - see the diagram below, phase-margin(Aol)=61.5°@Riso=100Ω.
When Riso is 51Ω, phase-margin (Aol) stays below recommended safe 45°. This is contrary to what I expected.
The circuit has been analyzed according to "10.3 TI Precision Labs - Op Amps: Stability - Spice simulation" presentation.
Am I missing something or what I observe is to be expected?