Can the LM1084 generate 2.5V output at 3A load from a 3.3V input source?
The LM1084 minimum dropout voltage at a 3A load is 0.95V; therefore it is not recommended for this application, which requires a dropout of less than (3.3V-2.5V)=0.8V at the full 3A load current. Instead, we recommend using the LM3478 switching regulator in the SEPIC topology. An example of a SEPIC topology circuit is shown in Figure 12 in the LM3478 datasheet. WEBENCH Power Designer supports the SEPIC application for LM3478 and other devices; enter your design requirements to obtain an appropriate solution.
