“Best Fit for Each Application” is Mandatory

With a view toward building a great family of DC/DC converters, ROHM is developing a wide variety of DC/DC converter ICs. The DC/DC converter comprises several types, including a synchronous rectifier type, and each type includes several control methods. ROHM’s DC/DC converter family is intended to provide “the best fit for each application”, offering a slew of advantages.

The “best fit for each application”, that is, using a power supply that precisely fits a given set of operating conditions, is an overriding factor. To answer the newer requirements for power savings and tight space, we need to increase the efficiency of the power supply to the maximum possible extent and minimize the footprint.

As just an example, suppose that we used a 3A power supply for a power supply unit in a circuit requiring 1A for the reason that it’s being used in other applications and those units are in stock. The 3A power supply, of course, can provide stable 1A power with an adequate margin to spare, at the expense of some wasted power.

The efficiency of a power supply is normally at maximum near the maximum output current for the power supply device, and it declines as the output current diminishes. In other words, in this example the power supply device would operate under poor efficiency conditions.

Another point is that 3A power supply devices require components that are capable of handling a current greater than 3A, in principle, irrespective of the load current. Such a power supply device requires capacitors and inductors with a high allowable current value, with attendant increases in cost and size. Furthermore, as a general rule 3A power supply ICs are more expensive than their 1A counterparts.

Hence, the “best fit for each application” is a mandatory requirement for the optimization of power supply units to answer the newer requirements.

The table below provides excerpts on members of the [BD9xx] series of the DC/DC converter family. In the case of the BD9Cx as an example, four models offering different output currents are provided. With the exception of the output current, these devices share the same basic specifications and the same pin assignment. If members of the line-up differ only slightly from one another in such a manner that there is no great gap between them in performance characteristics, the designer can choose an IC that is the closest to a given design goal. In addition, if a need arises in the midst of a design process to provide a higher output current, substantial design modifications can be avoided by choosing a model that is one rank higher in the series.

▶ List of the DC/DC converter family lineup (PDF）