Introduction

　　Everyone wants more power in less space. However， the task of designing a power supply is easy to describe but diffi cult to execute. How does a designer select an optimal set of components that yields the best possible power supply in terms of size， cost and performance？ Well， it is easier if the selection is reduced to only a handful of components.

　　For instance， the LT?3681 reduces parts selection to only a few passive components by integrating all of the power semiconductors necessary to make a buck converter into a single package. Don’t think that this high level of integration limits the usefulness of this part. The LT3681 accepts inputs from 3.6V to 34V， provides excellent line and load regulation and dynamic response， and offers a high effi ciency solution over a wide load range while keeping the output ripple low during Burst Mode? operation. Furthermore， its frequency is adjustable from 300kHz to 2.8MHz， enabling the use of small， low cost inductors and ceramic capacitors.

　　A Small， Simple Solution

　　The LT3681 integrates a wide input voltage range， high performance buck controller， power switch， high side bootstrapping boost diode and a power Schottky diode. All of these attributes are crammed into a tiny but thermally effi cient 14-pin 3mm × 4mm DFN package. So， all a designer needs to implement a full-featured buck converter is to add the output LC fi lter and a few passives.

　　The most obvious advantage of having the power Schottky diode integrated into the LT3681 is space savings， reducing the amount of board space required by the complete regulator by 15% or more. Moreover， the power Schottky diode has been optimized for the intended operation of the LT3681， so there is no need to agonize over fi nding the perfect form， fi t and function diode for the application. Figure 1 shows a schematic of the LT3681 producing 5V at 2A from an input of 6.3V to 34V and Figure 2 shows the effi ciency for a 12V input.