Requirement: Number of Voltages and Voltage Levels
The SCA shall operate on two 5 V inputs, one for analog circuitry and one for digital circuitry. Both voltages are referenced to separate grounds, i.e., analog and digital.
Limiting to 2 operating supply voltages avoids multiple power supply runs to the chip through areas where the number of available lines are severely limited. Also, the two supply concept has been used in past designs successfully, so represents a low risk. Two supplies are the minimum needed to assure adequate decoupling between noisy digital switching circuits and charge sensitive analog circuits.