Inductors are the largest components in POL converters and are hard to integrate. With the PSI2 concept it is possible to reduce the size of the POL converter by integrating all other components into the Inductor.
Because the miniaturization of products is increasing steadily, the efforts are now on reducing the overall size of the POL. The performance of semiconductors has improved in the last years to the point where MOSFETs now represent almost perfect switches and also capacitors have improved dramatically as a result of new dielectrics as well as improved manufacturing techniques. But in the meantime, the improvements in magnetic components have been much smaller and there are no exciting breakthroughs on the horizon. The result is therefore a POL where most of the space is allocated to the inductor.
The traditional POLs using discrete components on a daughterboard have given way to low profile integrated modules with all components mounted internally in one single module. These modules, also known under “Power Supply in Package” or “PSiP” are meanwhile offered in this format by a growing number of suppliers. The available output current of PSiP modules varies from a few mA up to 20 A, with the most common requirements being between about 3 A and 10 A.
Most PSiP manufacturers use a design approach where the single components IC, FET switches and inductor are mounted alongside each other on a small circuit board or lead frame, and are then encapsulated in some type of potting compound or injection moulded plastic housing as illustrated in Figure 1. For a new range of high power density, low profile POLs with high efficiency, Sumida has taken a different approach. Instead of mounting the inductor alongside the other components, all components are mounted inside the inductor in the Sumida module. The entire package is made of magnetic material instead of inert plastic fillers, allowing the largest volume for the inductor coil and the lowest possible DC resistance. Sumida calls this approach “Power Supply In Inductor” or “PSI2”. Figure 2 illustrates the concept of the Sumida PSI2 module.
A small cavity in the bottom side of the inductor allows space for the controller, the FETs and other components on the circuit board, which forms the base of the module. The bottom side has LGA pads. The inductor itself uses a custom-built core as well as a custom-built coil, and is carefully optimized to use the available volume the best possible way. With the correct choice of magnetic materials and coil design, this technique can offer an outstanding POL performance despite the small dimensions of the low profile module.
12 V input, 6 A POL module using PSI2
Using the PSI2 technique, a 12 V input/5 V output POL with a 6 A current rating can be realized in a module with only 9 mm x 15 mm and a height of only 2.8 mm and this with only minimum losses. Efficiency exceeds 94% at full load, with only about 1.8 W losses. In contrast, a comparable part with the same package size and utilizing the typical PSiP structure (Figure 1) was measured at only about 91% efficiency under the same load conditions, with losses of about 2.8 W. The comparison is shown in Figure 3.
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