The PCB layouts explained up to this point have all assumed the step-up converters using diode rectification (asynchronous rectification) described in "Current Paths in Step-up DC/DC Converters", but in this article, PCB layout is explained for cases in which a synchronous rectification type IC is used.
PCB Layout for Synchronous Rectification Step-up DC/DC Converters
In step-up DC/DC converters also, like step-down DC/DC converters, there are diode-rectified (asynchronous rectification) and synchronous rectification devices. In this chapter, we have explained board layouts using diode rectification ICs, which are the essence of these devices; but in recent years an increasing number of synchronous rectification step-up converter ICs have also appeared, and so here we explain important points of layouts for synchronous rectification designs. It should be noted that the evaluation boards, circuit diagrams, and layout examples presented in the first discussion, "The Importance of PCB Layout Design", were for synchronous rectification designs.
In the case of synchronous rectification, the freewheel diode D2 is integrated within the IC as the switching transistor Q2H, and so an example with an internal switching transistor is shown. A layout for the diode rectification design that has been explained in previous articles is also shown for comparison.
Points to consider regarding input and output capacitors, inductors, switching nodes that include inductors, thermal vias, feedback paths, and grounds are similar to those for the diode rectification circuits explained previously. And similar considerations relating to a snubber circuit to deal with high-frequency spike noise also apply.
・Points to be aware of in PCB layout are basically the same for diode rectification and for synchronous rectification