Getting The Most Out Of Your DC/DC Converter

When designing with switching regulators, the choice of external components can greatly affect the DC/DC converter’s performance in terms of efficiency, ripple voltage and load transient response. Using its wide range of DC/DC ICs, both step-up and step-down, Torex provides tips for selecting FETs, inductors, diodes and capacitors in order that the most suitable components and component values are chosen so that the optimum performance, depending upon the application requirement, can be achieved.

Andy Scott, Marketing Manager for Torex in Europe, commented: “The new guide is launched as a tool to not only complement DC/DC design work, but also as a simple way to enable designers to brush up on their understanding of the different aspects of the DC/DC and how the different external components relate to performance.”

After a basic review of the DC/DC converter, looking at characteristics, types and basic operating principles, the guide then goes into more detailed explanations of clearly defined aspects of the device’s characteristics, starting with choice of switching frequency.

There are certain associated trade-offs when deciding between a low switching frequency (1.2MHz) device and higher frequencies (3MHz); using Torex’s XC9237 synchronous step-down DC/DC converter as an example, it is easy to demonstrate that although higher switching frequencies give the benefit of lower ripple voltage, this is offset by slightly lower efficiency.

For those DC/DC’s that require an external FET, differing RDS and CISS values can also affect overall efficiency. Although FETs with a low RDS value enable higher output currents to be achieved, with higher efficiencies at those higher loads, the efficiency at light loads is poor. The advice is not to use a FET that has a driving capability of unnecessarily large current as it is often detrimental to the overall performance.