Part # AN1485 datasheet

Part Manufacturer: ST Microelectronics

ST Microelectronics


Part Details:

AN1485 APPLICATION NOTE MDmeshTM PERFORMANCE EVALUATION IN A CONTINUOUS MODE PFC BOOST CONVERTER G. Belverde - M. Melito - A. Raciti - M. Saggio - S. Musumeci 1. ABSTRACT A new high voltage MOSFET structure is presented which results in static as well as dynamicperformances far ahead conventional Power MOSFET devices. The impact of the particular features ofthe device is analyzed and quantified in a case study regarding a DC-DC boost converter, which is usedin a power factor corrector (PFC) converter. Results obtained from the analysis of the electrical andthermal behavior of the component in the specific are discussed. 2. INTRODUCTION. Standard technology for high voltage suited Power MOSFETs has been dramatically improved, thus thephysical limit in terms of reduction of the device s on-state resistance is going to be reached. In fact, sucha device parameter is strongly affected by the drain resistivity value, which is designed according to therequirements of the high voltage blocking capability. Recently, an innovative concept of Power MOSFETdesign has been proposed that is able to enhance the device s performance [1, 2]. In these new devicesthe charge balance makes the electric field constant over the whole drain volume in spite of the lowresistivity in this conducting region. In breakdown conditions the electric field has a value almost equal tothe critical one for silicon. In this paper the main issues of process technology are shortly recalled and discussed. The static anddynamic characteristics are shown aiming to evaluate the advantages of the new device in comparison tostandard Power MOSFETs having both the same rated voltage and current carrying capability. Finally,the evaluation of the performance is focused on in a specific application, in particular in a boost-basedpower factor corrector (PFC) converter. 3. TRENDS ON POWER MOSFET (MDmeshTM) DEVICE TECHNOLOGY. A revolutionary three-dimensional design of the drain device volume is at the basis of the MDmeshTMMOSFET device. The extension of the top strip layout to the whole drain volume, by p-doped columninsertion under device stripes, allows a strong resistivity reduction of the conduction n-doped layer andan impressive decrease of the device s on-state resistance when compared to a conventional MOSFET[1]. The cross section of an MDmeshTM device is depicted in figure 1, where both the strip layout and thecolumn insertion under the device stripes are shown. As a consequence of this approach, the knowntheoretical limit of performance for vertical Power MOSFET devices decreases. In fact, the MDmeshTMMOSFET overcomes this limit allowing a mass production of devices with improved performance andreduced area. For example, a 500V MDmeshTM MOSFET is almost three times smaller than aconventional MOSFET having the same blocking voltage. November 2001 1/14 AN1485 - APPLICATION NOTE Figure 1: Three-Dimensional Cross Section Of MDmeshTM Device N-SOURCE P-MESH GATEFINGER DRAIN SUBSTRATE BACK METAL The static output characteristics of an MDmeshTM MOSFET in comparison to a standard device with thesame silicon area are reported in figure 2. Moreover, simulation analysis and theoretical considerationsshow that in MDmeshTM technology the device s on-state resistance increases linearly as function of thebreakdown voltage, according to the traces shown in figure 3. The direct consequence of this result isthat the extension of the MDmeshTM MOSFETs towards higher blocking voltage values will continuallyincrease the advantages of this technology. The fabrication of a 1000V MDmeshTM MOSFET will require,as expected from the design, a silicon area seven (7) times smaller than a conventional MOSFET withthe same on-state resistance and blocking voltage capability. This will cause a package reduction and amajor improvement in any application based on these devices, as consequence of the strong reductionobtained on volume and weight of the board. The extension to very high blocking voltage of MDmeshTMMOSFETs will represent a real revolution in high voltage converter applications. Figure 2: Static Output Characteristics (I/V Curves) Of An MDmeshTM (STP12NM50) And AStandard MOSFET Having Equal Silicon Area 1816 MDmeshTM 14 Std Technology ) Vgs=10V 12 (A 10 sId 864 Vgs=6V 20 0 1 2 3 4 5 6 7 8 9 10 Vds(V) 2/14 AN1485 - APPLICATION NOTE Figure 3: Standard MOSFET and MDmeshTM Dependence Of On-State Resistance As A FunctionOf The Breakdown Voltage 1 0 0 0

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