Research On Key Technologies Of 600V GaN Isolation Gate Drive

In the 600V high-voltage power supply application?PFC and LLC?,the switching loss is very large in hard-switching mode,which mainly uses soft-switching and resonance technology to reduce switching loss.The traditional solution uses Cool MOS,but due to the existence of its body diodes and large Q_G and Q_OSS,the reverse recovery has been solved badly,EMI is poor,power loss is large and switching frequency is limited in the implementation of soft-switching mode.Compared with Si devices,the C_OSS of GaN have small nonlinearity with V_DS variation,and GaN can obtain smaller Q_OSS under the same device on-resistance.Because of smaller Q_G,It can realize shorter resonance period and reduce conduction loss of resonant converter in the soft-switching applications,achieving higher switching frequency and power density,which especially suitable for the development trend of miniaturization of power modules in the future.Currently,enhancement GaN power devices with voltage ratings of 100V to 650V are commercially available,and the mainstream technology solutions for this function are Cascode and p-GaN.However,there are still many challenges in practical applications.The scheme of Cascode poses a great threat to device reliability because of the parasitic parameters of its interconnect and the presence of Si body diode.Due to the low V_TH and the withstand voltage of V_GS,p-GaN has a small safety margin for device operation,which increases the difficulty of driving IC and system design while affecting system reliability.Therefore,depletion GaN devices are considered to be more attractive in high-voltage and high-efficiency applications.This paper is based on a depletion GaN device,compared with the traditional Cascode-drive depletion device scheme,and proposed a method called Direct-drive.For a typical half-bridge power topology application,the dv/dt caused by the switching node is as high as 200V/ns at 600 V:1.The common mode noise current caused by the high dv/dt will bring great crosstalk to the logic input signal;this paper analyzes the size of the parasitic isolation capacitors of various isolated driver circuits,and uses digital isolators to effectively isolate the crosstalk between the input logic signal and the drive signal;2.Large dv/dt causes GaN to be turned on accidentally,causing the problem of punching through the upper and lower tubes.This paper proposes the driving method of Direct-drive,which uses negative voltage shutdown technology to control effectively the ringing and false opening of the gate voltage;3.The problem with the Direct-drive approach is that the negative-voltage shutdown increases the gate charge Q_G required to turn on the GaN device.This paper uses the physical mechanism of the segmented slope control without affecting the switching speed and efficiency to solve the problems and optimize the EMI characteristics;4.Negative voltage shutdown will make the various switching signals inside the chip become very complicated.This paper proposes a high-speed and low-power negative-voltage level shifter circuit to realize the level signal switching between power rails.Based on the 60V 0.35?m BCD process,the sub-circuit and the whole system are simulated and verified by the circuit simulation platform Cadence.Under the condition of 1MHz switching frequency,the propagation delay?turn on?of the chip system can be20ns.The turn-off delay is 30ns and the maximum common-mode interference capability is 140V/ns.