Research And Design Of High Speed Synchronous Rectification Controller Chip

In recent years,with the continuous improvement of integrated circuit design and manufacturing level,switching power supply products are developing towards high efficiency,high integration,small size and high power density.However,the traditional way of using diode as switching power supply rectifier will produce high rectification loss in the context of low voltage and high current applications,which is not conducive to the improvement of switching power supply efficiency.Therefore,the synchronous rectification technology is proposed,that is,the power MOSFET with extremely low on state resistance is used to replace the traditional diode as the rectifier,which can greatly reduce the tube voltage drop of the rectifier,maintain low on state loss and improve the conversion efficiency of the switching power supply.In addition,in order to meet the demand of high power density of switching power supply,the operating frequency of switching power supply needs to be increased as much as possible,and the operating frequency of related control chips also needs to be increased.Based on the above research background,this paper designs a high-speed synchronous rectifier controller chip（single channel）,which has important research significance for realizing high power density,high integration and high efficiency of switching power supply.The high-speed synchronous rectifier controller chip（single channel）designed in this paper can work normally in the flyback topology under DCM（Discontinuous Conduction Mode）and CCM（Continuous Conduction Mode）.The maximum operating frequency can reach 1MHz and has short turn on propagation delay and turn off propagation delay.The main functional modules in the chip include:turn on threshold comparator and turn off threshold comparator,proportional gate driver,minimum turn on time generation circuit,adaptive minimum turn off time generation circuit,standby mode detection circuit,etc.Considering the uncertainty of the actual working environment of the chip,the related protection circuit and auxiliary circuit of the above functional modules are designed.The innovation of the research content includes the design of proportional gate driver and adaptive minimum turn off time generation circuit.The proportional gate driver can realize the phased output of the gate driving voltage,which can effectively reduce the turn off propagation delay of the chip and reduce the gate voltage stress of the switch tube;The adaptive minimum turn off time generation circuit can adaptively adjust the minimum turn off time according to the switching frequency of the synchronous rectifier,and set the minimum turn off time to 50%of the turn off time in the previous cycle of the synchronous rectifier through the logic circuit and voltage division design,so as to shield the ringing phenomenon of the voltage V_DS of the synchronous rectifier in the DCM mode.In addition,since LLC（inductance-inductance-capacitance）resonant topology has been widely used in the field of switching power supply in recent years with its advantages of high efficiency and high power density,this paper multiplexes and optimizes the proportional gate driver and related control logic circuits in the above single channel synchronous rectifier controller,and integrates them into a dual channel chip to drive two synchronous rectifiers at the same time.Therefore,the integration of LLC resonant converter can be effectively improved.Based on 0.18μm BCD process,the circuit design and simulation analysis of the chip sub module and the overall system are carried out by using Cadence simulation tools,and the layout drawing of two chips（single channel and dual channel）is completed.The simulation results show that the two chips can normally generate synchronous rectification driving signals.The maximum working frequency of the high-speed synchronous rectification controller chip（single channel）can reach 1MHz,and the maximum conversion efficiency can reach 91%,both of which meet the design index requirements.