Research And Design Of A Multi-Mode And Wide-Input Buck Converter Based On PCM Control

With the development of new energy and communication equipment,in industrial and automotive applications,the application range of the voltage required by the power supply system is usually much wider than that required by the power supply system of portable devices,and there are multiple input voltage requirements in the power supply system,which requires that the power supply chip has a wide input range,and its realization mainly benefits from the development of high-voltage BCD technology.In addition,the requirements for conversion efficiency and low EMI of power supply chips are also increasing.Some applications need more accurate switching frequency to avoid frequency interference,or multiple power supply ICs on the same PCB circuit use the same switching frequency,so that they have the same EMI characteristics and improve the flexibility of application.The design of multiple working modes can significantly improve the scope of application of power supply chips.Therefore,thesis designs a peak current mode(PCM)control loop,which is used for a buck converter of wide input and multiple operating modes.It uses a 0.25μm BCD process with a maximum withstand voltage of 80 V.Its maximum average current is 3.5A,and the input voltage range is 4V to 65 V.The four operating modes are switched through an external pin SYNC/MODE signal,which are Pulse-skipping Mode(PSM),spread mode and external clock synchronization mode with pulse hopping,and burst mode for low power consumption.By using a high-voltage NJFET,the designed bandgap reference circuit has the characteristics of wide input range and high power supply rejection ratio.Considering that under high input conditions,the LDO loss of supplying power to internal submodules will be large,ultimately affecting the overall conversion efficiency of the buck converter,thesis designs a power supply pin switching strategy for LDO.Under high input voltage,the power supply voltage can be switched to a low input voltage through external pins,or directly connected to the buck output Vout,thereby effectively improving the conversion efficiency of the buck at high input voltage.Finally,the overall simulation verification of the designed chip,such as wide input,light load efficiency,and transient response,was performed.At a frequency of 1 MHz,the system can slowly start through a soft start circuit for 5.5V input and 5V output and65 V input and 5V output,that is,close to the maximum and minimum conduction times.Within the range of 5.5V to 65 V input voltage,the linear adjustment rate is 0.26 mV/V.And when the BIAS of the LDO is connected to Vout at a 12 V input and 5V output and frequency of 1MHz,the efficiency can reach 95.3%.For transient response,when the input jumps from 12 V to 5.5V and then to 20 V,the output undershoot and upshoot sizes are 32 mV and 38 mV,respectively,with recovery times of 57μs and 65μs.When the load jumps up and down within 1μs for 1A,the Vout undershoot and upshoot are 43 mV and45 mV,respectively,with recovery times of 55.8μs and 51.8μs.The simulation results can meet the design requirements.