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STM32F3 Opamp needed guidance

Question asked by ea4frb on Jan 30, 2013
Latest reply on Feb 6, 2013 by ea4frb
In an application using the STM32F3xx, I am using the OPAMP in PGA mode to amplify an external 1 kHz signal to the ADC converter. The signal is provided AC coupled to the OPAMP non-inverting input.

If I program the OPAMP in follower mode everything works fine. The ADC reads the right values and the signal in the OPAMP output pin is correct and centered around VDDA/2.

However, if I program for PGA mode and specially with higher gains, the OPAMP works erratic. In some cases the output is clipped around VDDA and sometimes around VSS. Probing with the oscilloscope in the OPAMP output pin, has effect in the behaviour and sometimes it makes it working fine.

I am wondering in the non-inverting configuration, what is the VREF level used and if it is programmable.

What I see it is a bit the lack of information and examples about the use of the OPAMP with the std peripheral library, e.g. for the calibration and for the VREF settings.

Any additional guidance on the OPAMP operation of hints about what could be the source of this problem, will be of great help.