Specifications-driven design space boundaries for Point-of-Load converters

This paper derives physical constraints for the output filter of a Point-of-Load (POL) converter. Time-optimal control theory is employed to translate the POL static and dynamic specifications into boundaries in the L-C design space, ultimately defining a set Σ of L and C values compatible with the application requirements. Outside the identified set Σ, no controller is capable of meeting the POL specifications; inside the identified set Σ, various degrees of approximation of the time-optimal response are possible, depending on the specific control approach in the field application. The identified set shows the minimum possible values of L and C such that the specifications can be met, which allows the designer to evaluate the impact of a practical controller implementation on the size of the output filter. The design space and boundaries for a digital PID controller are derived, leading to a combined L-C filter and controller design approach. Experimental results validating the design space boundaries are presented for a 12 V-to-1 V, 20 A POL converter.