A More Accurate Power MOSFET Current Mirror Sensing Scheme in Synchronous Buck Converters

Abstract

This paper presents a current-mirror sensing scheme for high-current trench MOSFETs in synchronous buck converters and implements in a three-die PQFN package capable of delivering 70-A current per phase. Current signal accuracy is critical in high-current multiphase converters that power CPUs, GPUs, DDR memories, and FPGAs in high-performance computers and artificial intelligence systems, since the current information is used not only in optimization of computer system performance and adaptive voltage positioning but also for current sharing between multiple phases and converter over-current protection. Inductor DCR and MOSFET RDS(on) current sensing methods have been used in synchronous buck converters for more than a decade, but the current sensing accuracy is limited to +/-10% and +/-5% respectively and becomes even worse when application conditions vary in wider ranges. Higher current reporting accuracy of the MOSFET current mirror sensing is experimentally verified using multiple synchronous buck converter boards, which are built to measure current sensing error of each power stage and to determine distribution of system current reporting tolerance. Smaller than +/-3%, 3-sigma current error is achieved over wide application ranges of ambient temperature and MOSFET gate drive voltage.