Yipeng Su

Gallium Nitride based 3D integrated non-isolated point of load module

The introduction of Gallium Nitride (GaN) based power devices offers the potential to achieve higher efficiency and higher switching frequencies than possible with Silicon MOSFETs. This paper will discuss the GaN device characteristics, packaging impact on performance, gate driving methods, and the integration possibilities using GaN technology. The final demonstration being an integrated 3D point of load (POL) converter operating at a switching frequency of 2MHz for a 12V to 1.2V buck converter with a full load current of 20A. This 3D converter employs a low profile low temperature co-fired ceramic (LTCC) inductor and can achieve a full load efficiency of 83% and a power density of 750W/in3 which doubles the power density of current integrated POL converters on the market today.

Optimization of a high density gallium nitride based non-isolated point of load module

The demand for future power supplies to achieve higher output currents, smaller size, and higher efficiency cannot be achieved with conventional technologies. There are limitations in the packaging parasitics, thermal management, and layout parasitics that must be addressed to push for higher frequencies and improved power density. To address these limitations, the use of integrated 3D point of load (POL) converters utilizing GaN transistors, low profile magnetic substrates, and ceramic substrates with high thermal conductivity will be considered. This paper will discuss the effect of parasitics on the performance of high frequency GaN POLs, methods to improve the circuit layout of a highly integrated 3D integrated POL module, and the thermal design of a high density module using advanced substrates. The final demonstration is a 900W/in3 12V 2MHz Alumina DBC GaN converter which offers unmatched power density compared to state of the art industry products and research.

Design and Evaluation of a High-Frequency LTCC Inductor Substrate for a Three-Dimensional Integrated DC/DC Converter

High operating frequency and integration technique are two main approaches to achieve high power density for the switching mode power supply. The emerging gallium nitride (GaN)-based power device enables a multimegahertz high-efficiency point-of-load (POL) converter with high current capability. The low-temperature cofire ceramic (LTCC)-based integration technique successfully extends the three-dimensional (3-D) integrated POL module from the low current level to the high current level (>10 A). This paper presents the low-profile LTCC inductor substrate design and evaluation for a multimegahertz 3-D integrated POL converter with large output current. The detailed study about the impact of frequency on the LTCC inductor shows that the high frequency not only shrinks the volume of the inductor, but also simplifies the inductor structure. The comparison between the LTCC inductor and the discrete inductor demonstrates that the LTCC inductor dramatically boosts the converter light-load efficiency due to its nonlinear inductance. Because of the low-profile design, the power density of the single-phase POL module with LTCC inductor achieves 1.1 kW/in3 at 5 MHz. The performance of the LTCC inductor can be further improved by the inverse coupling, which results in more than 40% core thickness and core loss reduction. Therefore, the power density of a two-phase integrated POL module is pushed to 1.5 kW/in3, which is around ten times of the power density of state-of-the-art industry products with the same current level.

Printed Spiral Winding Inductor With Wide Frequency Bandwidth

Winding parasitic capacitance is a major factor limiting the bandwidth of an inductor. In this paper, 1) the traditional, 2) the alternating, and 3) the partial alternating winding methods are evaluated for the multilayer printed spiral winding inductors for megahertz operations. The self-capacitances of various winding structures are estimated by the summation of parasitic capacitance among the turns of a winding. The electric field energy distributions in the inductors are derived from the voltage profiles to illustrate the relative magnitudes of winding parasitic capacitances. The results show that parasitic capacitance reduction can be achieved by reducing stored electric field energy. The partial alternating winding method is found to have the widest frequency bandwidth with reduced number of through-hole vias for multilayer printed spiral winding design. The theoretical analysis has been confirmed with practical measurements. The results provide useful information for the optimal design of coreless or core-based high-frequency planar magnetics.

On the relationship of quality factor and hollow winding structure of coreless printed spiral winding (CPSW) inductor

The principle of using hollow spiral winding is not novel, but the study on this topic is far from complete. In this paper, how hollow the central region of the Coreless Printed Spiral Winding (CPSW) inductor should be in order to achieve the maximal quality factor value Qmax is explored. A new parameter, namely the ratio of the inner hollow radius and the outer winding radius τ = Rin / Rout, is proposed as an indicator for optimization and used to quantify how hollow a spiral winding is. With the aid of Finite Element Analysis (FEA), the relationship between τ and Qmax, which depends on the operating frequency and the dimensional parameters of CPSW inductor, is established. For a specific operating frequency, it is discovered that if the conductor width is comparable with the skin depth, or the conductors are placed relatively far away from each others, the hollow design of the CPSW inductor has little improvement on Q but reduces the inductance. On the contrary, if the conductor width is much larger than the skin depth and the conductors are placed relatively close, the hollow spiral design is recommended. The optimal range of τ with which the Qmax can be achieved is found to be around 0.45 to 0.55.

High frequency integrated Point of Load (POL) module with PCB embedded inductor substrate

In this paper, a novel alloy flake composite material is used to demonstrate the PCB integrated magnetic component with low temperature fabrication process. The most important benefit of the alloy flake composite core is easy to be patterned into any desired shape for integration. Compared with the traditional flake composite, the permeability and core loss of the new flake composite are improved prominently, by doing some lateral alignment of the flake and increasing the volume ratio of the alloy. The layerwise magnetic core is sandwiched into multilayer PCB using conventional PCB laminating technique. It has been proved that the manufacturing process, such as laminating, cutting and drilling, has very little impact on the magnetic properties of the flake core. Based on a simple 4-layer PCB substrate with embedded core, the megahertz 3D integrated Point of Load (POL) modules are built, which achieve more than 700 W/in3 power density. The PCB modules survive after hundreds of thermal variation cycles, validating the reliability and compatibility of the alloy flake composite material with PCB integration. In addition, the application of standard PCB process reduces the cost for manufacturing such integrated modules due to the easy automation and low temperature process.

Characterization of Low Temperature Sintered Ferrite Laminates for High Frequency Point-of-Load (POL) Converters

Low profile magnetic components and associated integration techniques are desired for design and fabrication of highly integrated point-of-load (POL) converters working at high frequency. The multilayer low-fire ferrite inductors can be fabricated as the magnetic substrate in an integrated POL converter with active components on top. This paper reports the characterization of magnetic property, microstructure, and chemical composition of commercially available low-fire Ni-Cu-Zn ferrites (ESL 40010, 40011, and 40012) and their mixed laminates. Permeability and core loss density were measured on toroidal cores sintered at 885 ° C for 3.5 h. The influence of superimposed dc bias on the magnetic property of ferrite laminates was also evaluated. The microstructure and chemical composition of low temperature sintered ferrite laminates were analyzed. The mixed laminate with alternating layers of ESL 40010 and ESL 40012 in 1:1 ratio presents the highest permeability and the lowest core loss density among all examined samples when dc bias is above 1000 A/m. Finally, a 12 V to 1.2 V, 15 A, high frequency (1.5-5 MHz) integrated POL converter with laminated ferrite inductor was fabricated and demonstrated to work at high efficiency with a power density as high as 1000 W/in3.

Improving the efficiency and dynamics of 3D integrated POL

The 3-Dimensional (3D) integrated non-uniform flux inductor has shown good performance in achieving high power density and high efficiency in Point of Load (POL) module design. In this work, both single-phase and two-phase coupled non-uniform flux inductors are designed to build an 18A POL module with a QFN package. The non-uniform flux inductors unique property of varying core loss at different load conditions is analyzed, and the two-phase coupled inductor design that considers both efficiency and dynamics is demonstrated. The module evaluation shows improvement in efficiency and power density in comparison to conventional design.

High-Density Integration of High-Frequency High-Current Point-of-Load (POL) Modules With Planar Inductors

Planar inductors made by mixed laminates of low-temperature sintered Ni-Cu-Zn ferrite tapes and metal-flake composite materials are used for high-density integration of point-of-load (POL) modules. Incremental permeability and core loss density were characterized on toroidal samples under high dc bias to demonstrate that both materials are suitable for application in high-frequency high-current POL converters. In order to realize a high power density POL module, a multilayer ferrite inductor laminated with alternating layers of ESL 40010 and ESL 40012 in a 1:1 ratio has been fabricated and integrated with the active layer. Meanwhile, standard printed circuit board (PCB) processing has been adopted for the POL integration with a PCB-embedded inductor using NEC-TOKINs metal-flake composite materials. These developed 3-D integration approaches can be used to reduce the footprint and increase the power density for POL converters. It has been demonstrated that the power efficiency of both POL modules with integrated planar inductors can achieve above 87% at an operating frequency of 2 MHz and an output current of 15 A. Additionally, no obvious efficiency degradation was observed on the integrated POL modules after a certain number of thermal cycling from -40 °C to +150 °C.

High frequency inductor design and comparison for high efficiency high density POLs with GaN device

High operating frequency and integration technique are two main approaches to achieve high power density for the switching mode power supply. With the emerging Gallium-Nitride (GaN) based power transistors, the switching frequency of a Point-of-Load (POL) converter can be pushed to several Mega-hertz, while the efficiency is still maintained more than 85%. In this paper, the low profile LTCC magnetic substrate are designed for a 5 MHz, 12 V to 1.2 V, 15 A, 3-D integrated POL module with GaN device. Different LTCC ferrite materials and inductor structures with different number of turns are considered and compared for this high frequency and high current POL application. With the LTCC inductor substrate and GaN device, the 3-D integrated POL module can achieve as high as 1kW/in3 power density and 84% efficiency at 15 A output current. As a benchmark, a SMT discrete inductor is designed and customized utilizing the commercial Ni-Zn bulk ferrite material. The comprehensive comparison demonstrates several benefit of the LTCC inductor substrate, such as ultra-low profile, capability of integration and the light load efficiency improvement.