A programmable bandgap voltage reference CMOS ASIC for switching power converter integrated digital controllers

In the ac-dc and dc-dc switching power converter, digital controllers offer many advantages over analog controllers including improved system reliability, flexibility, and ease of integration and optimization. The challenge is to integrate as much as possible all of the functions required by the digital controller into one application specific integrated circuit. A key function required by the integrated digital controller is a programmable bandgap voltage reference. In this paper a description of the theoretical development, implementation and experimental results to date for a programmable bandgap voltage reference is presented. This reference is novel in that it is programmable via a system on chip bus and it comprises a bandgap voltage reference that is digitally modulated by a first order delta sigma modulator and then smoothed by a passive RC filter. The key design objectives are to provide a programmable output from 0 V to 2.5 V dc approx. with 10b resolution and a temperature coefficient of less than 100 ppm/°C over a temperature range from -55 °C to +125 °C. Another key design objective is to integrate all passive and active components used into one 0.35 micron full custom mixed signal CMOS ASIC.