sorry, my mistake. phone stays bright when on AC and when Im using it. It surely turns off, if Im not working on it. But without charging it used to go off after some sec (no matter what time i configured in settings/ if i set it to 2min, it would turn off after 2 sec, even when I was typing or sth). Idk why, but after one day of buggy behavior, my phone now seem to work fine again. Funny thing... pff