Buck-Boost Controller Simplifi es Design of DC/DC Converters for Handheld Products:A number of conventional solutions have been available for the design of a DC/DC converter where the output voltage is within the input voltage range—a common scenario in Li-Ion battery-powered applications—but none were very attractive until now. Conventional topologies, such as SEPIC or boost followed by buck, have numerous disadvantages, including low effi ciency, complex magnetics, polarity inversion and/or circuit complexity/cost. The LTC®3785 buck-boost controller yields a simple, effi cient, low parts-count, single-converter solution that is easy to implement, thus avoiding the drawbacks associated with traditional solutions. High Effi ciency Controller Capabilities The LTC3785 serves applications requiring input and output voltages in the range of 2.7 to 10V—ideal for applications powered from one or two Li-Ion cells or multiple cell NiMH, NiCad or Alkaline batteries. It supports a single inductor, 4-switch, buck-boost topology, which is ideal for an output voltage that is within the input voltage range. The high level of integration yields a simple, low parts-count solution. The LTC3785 provides for currentlimit and shutdown in all modes of operation (which is not normally available with boost converters). Very high effi ciency is achieved by synchronous rectifi cation, high side drive (allowing the use of N-channel MOSFETs), RDS(ON) current sensing, and Burst Mode® operation for effi cient light load operation. Protection features include soft-start, overvoltage, undervoltage and foldback current-limit with burp-mode or latch-off for extended faults. 3.3V, 3A Converter Operates from 2.7V – 10V Source The circuit shown in Figure 1 utilizes the LTC3785 controller to produce a synchronous, 4-switch, buck-boost design. It provides a fi xed 3.3V, 3A output from a 2.7V – 10V input. It is short-circuit protected: the controller offers a choice of recycling or latch-off protection for severe overload faults.