A System-on-Chip (SoC) includes first and second voltage supply pins configured to receive first and second supply voltages, respectively, a first supply path beginning at the first supply pin, and a supply proportion checker. The first supply path includes a first plurality of voltage supply nodes and a supply switch coupled between adjacent voltage supply nodes, wherein each node is configured to provide a corresponding internal voltage supply to a corresponding portion of the SoC. The supply proportion checker is coupled to receive the corresponding internal voltage supply from each voltage supply node, and configured to determine whether a first internal voltage supply supplied by a first supply node of the first plurality of nodes has a legitimate proportion to a second internal voltage supply supplied by a second supply node of the first plurality of nodes, wherein the legitimacy is checked using only resistors which do not require trimming.