EMI reduction technique with noise spread spectrum using swept frequency modulation for hysteretic DC-DC converters

Due to the development of industrial technology, miniaturization and high efficiency of the switching power supply which is the mainstream in the power supply circuit are realized. On the other hand, countermeasures against electromagnetic interference (EMI) generated by switching are the subjects. It is known that output ripple and load response deteriorate by reducing EMI, but the relationship has not been studied. Also, as a method of EMI reduction, M series circuits have been used in the past, but this method had the disadvantage that the attenuation amount at the spectrum level and the diffusion width are hard to understand quantitatively. In this paper, we propose clock frequency sweep method as EMI reduction method and clarify the correlation between EMI reduction amount and various characteristics in constant on time (COT) ripple control DC-DC converter by simulation and implementation.