June/July 2021

www.apec-conf.org APEC 2021 29 www.power-mag.com Issue 3 2021 Power Electronics Europe more than 2x higher than the maximum rated DC-current (20 A at room temperature). This is important to ensure not only good on-state operations, but also fast switching and fast discharge of the output capacitance (C oss ) during turn-on transients. Finally, the SCCL technology does not degrade the quality of the field-plate dielectric isolation, as no increase in 650-V off-state leakage current has been observed with respect to the standard device. In order to assess the dynamic performance of the SCCL device, dynamic R on tests and inductive switching tests were carried out with a resistive load of 80 Ω at a DC-bus of 480 V. On-state pulse-width and duty-cycle are 2 µs and 0.01 % respectively. The device remains in the off-state for most of the Automotive GaN DC/DC Converter 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 sensing technique. Xugang Ke, Analog Devices Power Products Group (xugang.ke@analog.com) Modern automotive-use application processors (APs) tend to operate with low voltage but high current. With a battery input voltage (V IN ) ranging from 3 to 40 V, nominal supply voltage of an AP is only around 1.2V. Wide- input DC/DC conversion is thus essential. For high efficiency and low cost, single-stage implementation is highly preferred. On the other hand, GaN FETs prove to work as better power switches over Silicon MOSFETs, owing to high channel conductivity, low parasitic capacitance and high breakdown voltage. Single-stage GaN based DC/DC converter Based on the AOT control, a single-stage 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 (t dead ). Accordingly, a sample-and-hold (S/H) based closed-loop dead time control is proposed to regulate t dead adaptively according to instantaneous input voltage (V IN ) and I O (Figure 1). It primarily consists of GaN power switches (M H &M L ) and a transient enhanced AOT hysteretic controller. The controller includes a main comparator (CMP) with adaptive slope generator (V SLP ), logic control with a load adaptive transient enhanced T ON timer and a sample-and-hold (S/H) based t dead controller. 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 5 MHz. In response to load steps between 0.5 A and 10 A, it achieves a 49 mV/29 mV V O 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 %. Figure 2 shows the chip layout. The die size is 1.65 mm? which includes an on-chip bootstrap capacitor (C BST ). Literature 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, APEC 2021 Procedings, pages 513-516 test time. The dynamic R on value was recorded after 60 s of operation to ensure the filling of the traps (if any). Results show that the relative increase between dynamic and static Ron is approximately +18 %. This is similar to the relative increase between dynamic and static Ron in standard devices and indicates that the SCCL blocking region does not exacerbate charge- trapping. Literature Short-Circuit Capability Demonstrated for GaN Power Switches, APEC 2021 Procedings, pages 370-375 Figure 1: Block diagram of the proposed transient enhanced AOT hysteretic converter Figure 2: Chip implementation of the AOT DC/DC converter