In this paper a commercial 28 nm FDSOI CMOS technology is characterized and modeled from room temperature down to 4.2 K. Here we explain the influence of incomplete ionization and interface traps on this technology starting from the fundamental device-physics. We then illustrate how these phenomena can be accounted for in circuit device-models. We find that the design-oriented simplified EKV model can accurately predict the impact of the temperature reduction on the transfer characteristics, back-gate sensitivity, and transconductance efficiency. The presented results aim at extending industry-standard compact models to cryogenic temperatures for the design of cryo-CMOS circuits implemented in a 28 nm FDSOI technology.