采用分段式自适应PWM/PFM调制的Buck型DC-DC转换器设计

为了在轻重负载条件下获得更高的转换效率，采用分段式结构和导通电阻更小的NMOS作为输入级，并采用PWM/PFM双调制方式，设计了一种Buck型DC-DC转换器。为解决PWM/PFM调制信号切换问题，采用零电流检测方式进行切换。利用断续导通模式(DCM)和连续导通模式(CCM)下端NMOS管导通时电感电压的不同，检测下端NMOS在导通时电感电压大于零的周期。当电感电压大于零的周期大于2时，则处于DCM模式并自动采用PFM调制模式，关闭一部分功率管以减小开关频率和功率管寄生电容，优化轻载效率；反之则处于CCM模式并采用PWM调制。仿真结果表明，在负载电流10～1 000 mA范围内，该电路可以在两种调制模式平稳切换，在800 mA时峰值效率可提升到96%以上。

Design of a Buck DC-DC Converter with Segmented Adaptive PWM/PFM Modulation

In order to achieve higher conversion efficiency for buck DC-DC converter under light and heavy load conditions, a segmented structure and an NMOS transistor with smaller conduction resistance were used as input stage, and a PWM/PFM dual modulation mode was used. To solve the switching problem of PWM/PFM modulation signals, the zero current detection method was adopted for switching. By using the difference between (DCM) and (CCM) inductance voltages when the low-side NMOS was turned on to detect the period when the inductance voltage of the low-side NMOS was greater than zero when it was turned on. When the period of inductance voltage greater than zero was greater than 2, it was in DCM mode, and the circuit automatically used PFM modulation and turned off a part of the power MOSFET to reduce the switching frequency and parasitic capacitance of the power MOSFET to optimize the light-load efficiency. Otherwise, it was in CCM mode, and the circuit used PWM modulation. The simulation results show that the DC-DC converter can switch smoothly between the two modulation modes in the range of 10-1 000 mA of load current, and the peak efficiency can be increased to more than 96% at 800 mA.