Just found-out about a really bad design of the SAML21 micro. In order to use it's DAC as an internal reference for the internal OpAmps I must output the DAC to it's IO pin (pin 3, in the case of DAC0). The problem is that pin 3 is shared with OpAmp0 negative input. It is then impossible to use the DAC0 AND the negative input of OpAmp0 at the same time...

So I won't be able to implement the following current source circuit with this micro.

For version 2 I will probably change the microcontroller...