DCDC: buck生成负压电源

参考应用笔记：Using the TPS6215x in an Inverting Buck-Boost Topology   https://www.ti.com/lit/an/slva469c/slva469c.pdf

 Using the TPS62125 in an Inverting Buck-Boost Topology  https://www.ti.com.cn/cn/lit/an/slva514b/slva514b.pdf