!THE COLLAPSE CREATES THE VACUUM
An inverting buck-boost converter takes a positive voltage and creates a negative one. It does not do this by pushing; it does it by pulling.
During the first phase, a switch connects the input voltage across an inductor to ground. Current flows, and a magnetic field builds.
Then, the switch opens, disconnecting the input entirely. The inductor is left hanging, holding a magnetic field that is rapidly collapsing. To maintain the flow of current, the inductor must act as a pump. Because of the circuit's geometry, the only way for the inductor to keep the current moving is to pull it from ground and shove it out the other side.
By pulling current from the output node toward ground, it forces the output voltage below zero. The positive input is disconnected, and the collapsing magnetic field creates a vacuum.
