一种新颖的同步BUCK芯片过零检测电路的设计

Design of a Novel Zero-Cross Detection Circuit for Synchronous BUCK Converter

同步BUCK变换器在轻载模式下会出现电感电流倒灌现象，这会使得芯片的效率大大降低。针对这一问题，设计了一款过零检测电路，该电路利用MOS管工作在线性区时的沟道电阻来产生过零检测比较器的负阈值电压，从而有效地限制了电流的倒灌；还设计了边沿隐匿电路，避免电路切换时引起的误触发。该过零检测电路基于0．5μmBCD工艺，在HSPICE软件上仿真验证，当系统温度在0～85℃变化时，负阈值容差为10mV，过零检测电路性能良好。

The phenomenon that inductor current flow backward appears when synchronous BUCK converter works in light load mode, and the efficiency of the system will be reduced. In response to this problem, a novel zero-cross detection circuit is designed. By using the channel resistance when the MOS transistor is working in linear region to realize negative threshold voltage for zero-cross detection comparator, the happening of current backward flowing is avoided. Edge occult circuit is also designed to avoid false triggering at switching moment. The zero-cross detection circuit is based on 0.5 μm BCD technology, and has been carried on HSPICE. The simulation result shows that the negative threshold tolerance is only 9 mV when system ranges in temperature from -25 ℃ to 50 ℃, and the zero- cross detection circuit works well.