Research And Design Of Low Switching Loss Driver For CoolMOS Device

As SMPS(Switch Mode Power Supply)developing towards higher frequencies,the switching losses of power switching devices account for an increasing proportion of system losses.Speeding up the switching speed helps to reduce switching losses,the fast switching device CoolMOS device comes into being,but the fast-switching will bring more serious EMI(Electro Magnetic Interference)problems to the system.By controlling the drive current along switch period,a trade-off can be achieved between EMI and switching losses to optimize switching performance.The traditional closed-loop control method adjusts the driving speed along switch period by detecting the status of the power switching device,the whole time is usually above 15ns,which makes the closed-loop control method not applicable to fast switching devices such as CoolMOS.A new control method needs to be explored,which can control the drive current along switch period even the device switching time is extremely short.In this thesis,based on deep analysis of the switching characteristics of the CoolMOS device,a programmable open-loop dynamic drive circuit is proposed.This scheme divides the switching process of the power switching device into a rough adjustment period of 2.5ns.In each rough adjustment period,a rough adjustment current is selected from 2⁸ levels and stay still,and a fine-tuning current is added on rough current,which can be selected from 2⁶levels and changes in units of 350ps.Then the dynamic accuracy of 350ps and 214adjustable current levels can be obtained.The scheme proposed in this paper includes several circuit modules:the oscillator circuit generates the rough adjustment period,the multi-level drive circuit generates the rough adjustment and fine adjustment current,and the logic control circuit controls the rough adjustment and fine adjustment current,and the EEPROM reading circuit achieves programmable control.The working process of the chip is:write the chip drive current timing data into the off-chip EEPROM in advance;after the chip is powered on,the on-chip EEPROM reading circuit reads the off-chip data;during the switch period,the logic control circuit selects the corresponding data to control the real-time changes of the rough and fine adjustment current.This driving scheme can achieve 350ps time accuracy and 2¹⁴ levels of current accuracy,and the driving current timing can be adjusted in a programmable way to slow down the switching speed when voltage and current spikes are generated during device switching,and speed up switching in other stages,which optimizes device EMI characteristics as well as reducing switching losses.This design is based on the SMIC EPI BCD180nm process.The simulation results show that under typical conditions,the rough adjustment period of the driver chip is 2.5ns,and the rough adjustment current has 2⁸ levels,each level is 17.2m A;the adjustable time step of fine adjustment current is 350ps,and there are 2⁶ levels,each level of current is 9.6m A;by changing the off-chip data,the drive current of the switching process can be adjusted to facilitate debugging,and then the best drive waveform can be achieved.