@User: There is a voltage clamp (or two) inside each power pad. The "lvclamp" and "hvclamp" cells have a low-voltage (1.8V) clamp or a high-voltage (3.3V) clamp, respectively. These are unconnected, so you can connect them to any of the supplies you want. DRN connects to the power rail of your choice, and SRC_BDY connects to the ground rail of your choice. There are two clamps inside the "lvclamp" cells, and they can be connected independently. The lvclamp cells additionally have a back-to-back diode with pin BDY2_B2B which should be connected to any ground rail; the other side of the back-to-back diode is shared with SRC_BDY_LVC1.