Dongbin Hou

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.

New core loss measurement method with partial cancellation concept

As an essential part in a power converter, the magnetic cores and their design play an important role in achieving high efficiency and high power density. Accurate measurement of the core loss is important to their optimization. To improve the measurement accuracy, previous methods were proposed to cancel the reactive voltage of the testing core by a cancellation capacitor or inductor. However, the value of the cancellation component is critical, and a small variation may induce a big measurement error, so extra effort is required to fine-tune the cancellation component value. This paper presents a new measurement method with partial cancellation concept that enables accurate core loss measurement at high frequency without requirement to fine-tune the cancellation component value.

Low profile coupled inductor substrate with fast transient response

The alloy flake composite magnetic material has been justified to be compatible with the conventional PCB manufacturing process. By embedding the layerwise core into multilayer PCB, a single-phase 3D integrated POL module achieves 700W/in3 power density and more than 85% efficiency. More important, the application of standard PCB process reduces the cost for manufacturing such integrated modules due to the easy automation and low temperature process. This paper tries to extend the same technology to multiphase POL module with coupled inductor. Combining the advanced control strategy, the high density and cost-effective two-phase POL modules are demonstrated for laptop VR application. The old low profile coupled inductor structure is modified slightly to improve its transient response. The air slots are added to reduce the transient inductance and enhance the coupling at light load condition. The non-linear inductance of the coupled inductor can be well controlled by using different slot structures. With the proposed coupled inductor structure, both low profile design and fast transient speed can be realized simultaneously.

Planar inductor structure with variable flux distribution —A benefit or impediment?

The planar inductor with lateral flux pattern has been successfully demonstrated as a substrate for the high density 3D integrated point-of-load (POL) module. By decoupling the flux distribution from the thickness of the core, both an ultrathin core structure and a high power density can be achieved simultaneously. However, the flux distribution in the lateral flux core is very non-uniform, which is totally against the conventional sense of the inductor design, namely the flux should be as uniform as possible. This paper reveals the DC flux and AC flux counterbalance phenomenon, by which the AC flux and core loss in the saturated core are essentially limited. The comparison between the core with variable flux and the core with relatively constant flux is presented, based on a specific high current POL application. The inductance density and the performance factor are proposed as the criteria to evaluate the utilization of the core for different magnetic structures. The variable flux core with multiple DC bias safely extended the operating points into saturation region, which gives better utilization of the core. The FEA simulation and measurement also prove that the core temperature is almost uniform for this planar core with variable flux, despite of 2~3 times difference in core loss density distribution. Because of the better thermal management capability, the planar core can be pushed to higher core loss density level than the core with relatively uniform flux, to realize lower total core loss and smaller core volume. In addition, the planar core saves more core loss at light load, due to the AC flux and core loss density redistributions.

Very High Frequency IVR for Small Portable Electronics With High-Current Multiphase 3-D Integrated Magnetics

As todays small portable electronics (smartphones, tablets, e-readers, etc.) becomes lighter, thinner, quicker, and smarter, the voltage regulator for the processor is expected to be efficient, miniaturized, integrated, and placed closer to the processor. In this paper, a concept of a very high frequency [tens of megahertz (MHz)] three-dimensional integrated voltage regulator (IVR) for small portable electronics is proposed. The magnetic characterization technique at tens of MHz is investigated, and the issues of and solutions for permeability and loss measurement are demonstrated. The LTCC and NEC flake materials are characterized and compared for the IVR inductor development. Both single-phase and five-phase integrated inductors are designed, fabricated, and experimentally tested at 20 MHz, featuring a simple single-via winding structure, small size, ultralow profile, ultralow DC resistance (DCR), high current-handling ability, air-gap-free magnetics, multiphase integration within one magnetic core, and lateral nonuniform flux distribution.

Magnetic characterization technique and materials comparison for very high frequency IVR

To efficiently power multi-core processors in todays computing devices, integrated voltage regulator (IVR) shows significant energy saving ability by dynamic voltage and frequency scaling. One key aspect in developing IVR is to design power inductors with small size and small loss at very high frequency. However, the challenge in very high frequency magnetic characterization is a major obstacle to accurately design and test the IVR inductors. In this work, the magnetic characterization technique at tens of MHz is investigated, and the issue and solution in permeability and loss measurement are demonstrated. The LTCC and NEC flake materials are characterized and compared at very high frequency for IVR inductor design.

Very high frequency integrated voltage regulator for small portable devices

As todays small portable devices (smartphones, tablets, etc.) becomes lighter, thinner, quicker, and smarter, the voltage regulator for the processor is expected to be efficient, miniaturized, integrated, and placed closer to the processor. In this paper, a concept of very high frequency (tens of MHz) 3D integrated voltage regulator for small portable devices is proposed. Both single-phase and 5-phase integrated inductor with NEC flake magnetic material is designed, fabricated and experimentally tested at 20MHz, featuring simple single-via winding structure, small size, ultra-low profile, ultra-low DCR, air-gap-free magnetic core, and lateral non-uniform flux.