Voltage-mode variable frequency control for single-inductor dual-output buck converter with fast transient response

This paper proposes a new control strategy technique called voltage-mode variable frequency (VMVF) control for single-inductor dual-output (SIDO) switching converter to achieve fast transient response and small output cross-regulation. A SIDO buck converter operating in continuous conduction mode (CCM) is taken as an example to analyse the operation modals with different equivalent series resistances (ESRs) of the output capacitor. It indicates that different ESRs can cause inductor current operating in three-step trend or four-step trend, and the critical ESR is derived. Finally, the time-domain simulation model of VMVF controlled CCM SIDO buck converter is established, and the transient performance and output cross-regulation are analyzed. It is found that, comparing to traditional common-mode voltage and differential-mode voltage control, VMVF control has improved transient response and reduced output cross-regulation. Furthermore, this control technique can work stably with different ESRs and even zero ESR.