An Automotive-Use 5MHz, 40V to 1.2V, Single-Stage AOT GaN DC-DC Converter with One-Cycle Transient Response and Load-Adaptive Dead Time Control

Abstract

To achieve a fast load transient response time in a switching power converter, constant on-time (COT) hysteretic mode control has been reported recently. However, due to the limitations on fixed on-time and mandatory minimum off-time, sluggish response and large voltage over-/undershoot are severe during extreme load transient scenarios. This paper presents a load transient enhance scheme which achieves adaptive on-time (AOT) transient response promptly and within one switching cycle, through instantaneous load change (∆IO) sensing technique. Based on the AOT control, a single-stage Gallium Nitride (GaN) based DC-DC converter is designed. Because a GaN switch inherently has no body diode and thus shows a high reverse conduction voltage, the efficiency is degraded with excessively long dead time (tdead). Accordingly, a sample-and-hold (S/H) based closed-loop dead time control is proposed to regulate tdead adaptively according to instantaneous input voltage (VIN) and IO. The converter is implemented using a 0.35-µm high voltage (HV) BCD process, accomplishing the DC-DC voltage conversion from 40 to 1.2V at 5MHz. In response to load steps between 0.5A and 10A, it achieves a 49mV/29mV VO undershoot/overshoot within one switching cycle. Thanks to the adaptive dead time control, the efficiency is improved by 4.8% at light load and 1.5% at heavy load, respectively, with a peak value of 89.5%.