| Automotive Ethernet can meet the technological,intelligent,and networked development of modern automobiles.It can achieve higher bandwidth of in-car data transmission and reduce the cost and cable weight of in-vehicle buses.Therefore,Automotive Ethernet Chips came into being.Aiming at the problem of low conversion efficiency caused by the use of internal linear voltage regulators in existing Automotive Ethernet PHY chips,this paper researches a buck circuit with high conversion efficiency integrated on the Automotive Ethernet PHY chip.Because the Automotive Ethernet PHY chip uses off-chip single 3.3V power supply,and the internal digital circuit operates at a power supply voltage of 1.2V,a buck circuit needs to be designed to implement this function.In this paper,a 0.13μm CMOS process library is used to design a Buck circuit,which mainly includes soft-startup,timer,zero-crossing detection,dead-time control,overcurrent protection modules,and bandgap reference module that provides a reference voltage;The designed softstartup circuit adopts the method of intermittently charging the output.The total circuit area is 0.004mm2.The circuit can achieve soft-startup without a large soft-start charging capacitor,which is easy to integrate on-chip and reduces the difficulty of implementation and risk.To optimize the transient response speed when switching from light load to heavy load,a control circuit is designed to enhance the transient response.Using spectre software for circuit module level and system level simulation,the results of simulation : when the output current is between 10 m A and 500 m A,the conversion efficiency at the three process corners of TT,FF,and SS can reach more than 85%,and the output current is 100 m A,at the case of FF corner,the conversion efficiency can reach a maximum of 94.28%;The inductor current changes are relatively stable during the startup process,and the output voltage changes gently without overshoot.The optimized Buck circuit is switched from light load to heavy load mode,and the recovery time is shortened from 2.266μs to 1.835μs,which significantly optimizes the load transient response speed when the light load jumps to heavy load.Finally,the layout design was completed using Virtuoso,which was taped out based on the 0.13μm CMOS process and has been integrated into the physical layer chip.The test results show: the circuit can achieve the normal function of 3.3V step-down to 1.2V ±25mV;Normal output current is 100.9m A,and conversion efficiency can reach 91%;Constant on-time generated by the timer is 410ns;Change of output voltage is relatively stable and gentle without overshoot during startup process,and finally stabilizes at1.194 V ± 25.25 mV,and the startup time is 250 us,and good performance of linear and load transient response.The results show that the designed Buck circuit meets the needs of digital circuits for Automotive Ethernet PHY chips. |
