This work deals with design of a fully-integrated DC-DC voltage converter with topology of Conventional Boost Converter (CBC), where mathematical approximations for accurate estimation of timing constraints of power switches are addressed. Firstly, the time diagram of current flowing through the inductor is approximated by linear and exponential approximations, and then the dependence of switch-on times of power switches is calculated. Mutual deviation of theseapproximations is then evaluated and accuracy of each is determined. Exponential approximation is acknowledged as more suitable for fully-integrated design while the linear approximation can be accurate enough for a system using discrete components. Findings are confirmed by simulations of the developed fully-integrated boost converter that was designed in a standard 65-nm CMOS technology. The evaluated accuracy relates to the fully-integrated design in standard CMOS technologies, including an on-chip inductor operating in the discontinuous conduction mode (DCM) The performed analysis and presented findings might be very useful also in education, where curricula of different subjects on integrated circuit design can be complemented with accurate circuit modelling during the design phase.