In the example shown on this slide it is clear the user needs a stepdown regulator. A linear regulator is out of the question, because its efficiency with Vout/Vin of 3.3/12 will be slightly higher than 25%. Also, the power dissipation at 3 A with an approximately 9 V drop will be around 26 W, which is not feasible to dissipate with a regular package/heatsink configuration. At 3 A, an integrated converter is a good choice; 80% efficiency is achievable even without a controller with external FETs, which is capable of >90-95% efficiency or more. At this point the customer can use the online simulation tool such as eDesign Suite, or the parametric search to select converters that meet the input voltage and output current requirements. A plot that shows the maximum Vin and maximum DC Iout will provide an immediate visual of the possible choices.