Hi Christian,
I've attached the modifications you would need to make this application suitably work with LM22670. You will need a 5A buck if you want 2A Iout. I would recommend using 47uF for C2, and 20uF combined C6 & C7. Please see attachment for schematic and recommendations.
(Please visit the site to view this file)
If you want -3.3V@2A output, remember for a conventional inverting buck boost topology, The average switch and inductor currents is the sum of Iin and Iout.
If you have any further questions, don't hesitate to ask.
Thanks,
Anston