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Stable system showing oscillations

Stable system showing oscillations

Stable system showing oscillations


There is something bugging me with a linear current regulator. The bode plot (attached) is showing a phase margin of 64.2 degrees, which means that the system is stable. When I plot the transient response, I can see the low frequency oscillations when I step the reference voltage, and these low frequency oscillations correspond to the 64.2 degrees phase margin. However, I can also see high frequency permanent oscillations (at around 43kHz). How is the Bode plot showing these oscillations? The gain at 43kHz is around -42.8dB, so any oscillations at that frequency should be attenuated. The only thing I can see is an abrupt change in phase around that frequency.
I've attached the Bode and the transient response. Could someone shed some light on this please?

Thank you very much,

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