The UCC3954, along with a few external components, develops a regulated +3.3V from a single lithium-ion battery whose terminal voltage can vary between 2.5V and 4.2V. The UCC3954 employs a simple flyback (Buck-Boost) technique to convert the battery energy to +3.3V. This is accomplished by referencing the lithium-ion cell's positive terminal to system ground. The negative terminal of the battery is the return point for the UCC3954. This approach enables the converter to maintain constant frequency operation whether the cell voltage is above or below the output voltage. An additional benefit of this technique is its inherent ability to disconnect the battery from the load in shutdown mode.