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Overview of Three-Dimension Integration for Point-of-Load Converters

Figure 1. Power density of POL converters.
High density integrated Point-of-Load (POL) converter is today's industry trend for portable electronic applications. Three-dimension (3D) integration concept is widely used for low current integrated POL converters. With this solution, a very low profile planar inductor is built as a substrate for the active components of the POL converter. By doing so, the footprint of POL converter can be dramatically saved, and the available space is also fully utilized. These 3D integrated POL converters can achieve 300-1000W/in3 power density, however, with considerably less current. In order to alleviate the intense thirst from the computing and telecom industry for high power-density high-current POL converters, the 3D integration concept needs be extended from low current applications to high current applications. In the past 10 years, CPES spent tremendous research efforts in this area and has successfully developed a series of technologies for high current 3D integrated POL converters. First, DBC based active layer was proposed to improve the thermal performance. Meanwhile, several methods were also proposed to reduce parasitic inductance of active layer, such as embedding bare die devices into active layer, building shielding layer. Then, Low profile LTCC inductors are used as the substrates for the 3D integrated POL converters. The thickness of the LTCC inductor substrate can be significantly reduced by pushing the switching frequency to several MHz. The performance of the LTCC inductor can be further improved by inverse coupling, which results in more than 40% core thickness reduction. Furthermore, the GaN HEMT was also evaluated and packaged for 3D integrated POL converter to help further increase switching frequency. Fig. 1 shows power density comparison between CPES 3D integrated POL converters with industry products. It can be seen that the proposed 3D integration technologies have successfully penetrated the barriers of high density integration for high current POL converters. Recently, A 5MHz, 12V to 1.2V, 20A, two-phase integrated POL converter with GaN transistors and LTCC coupled inductor is demonstrated with power density as high as 1000 W/in3, which is a factor of 10 improvements compared to industry products at the same current level.
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