Only for routing AGND, the respective Analog Block needs to be powered. The block can be power by configuring bits 1 and 0 in ACBxxCR2 resistor. This is not a necessity for routing RefHi and RefLo at the output pin. You can also power the SC Blocks by making the The Analog Power setting as SC On / Ref x in Global Resources. If the power setting is SC Off / Ref x, all SC blocks will be turned off and the ADC will not work.