Application Note AN 2012-04 V1.0 April 2012 500V CoolMOSTM CE 500V Superjunction MOSFET for Consumer and Lighting Applications IFAT PMM APS SE SL René Mente Francesco Di Domenico 500V CoolMOSTM CE Application Note AN 2012-04 V1.0 April 2012 Edition 2011-02-02 Published by Infineon Technologies Austria AG 9500 Villach, Austria © Infineon Technologies Austria AG 2012 All Rights Reserved. Attention please! THE INFORMATION GIVEN IN THIS APPLICATION NOTE IS GIVEN AS A HINT FOR THE IMPLEMENTATION OF THE INFINEON TECHNOLOGIES COMPONENT ONLY AND SHALL NOT BE REGARDED AS ANY DESCRIPTION OR WARRANTY OF A CERTAIN FUNCTIONALITY, CONDITION OR QUALITY OF THE INFINEON TECHNOLOGIES COMPONENT. THE RECIPIENT OF THIS APPLICATION NOTE MUST VERIFY ANY FUNCTION DESCRIBED HEREIN IN THE REAL APPLICATION. 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Life support devices or systems are intended to be implanted in the human body, or to support and/or maintain and sustain and/or protect human life. If they fail, it is reasonable to assume that the health of the user or other persons may be endangered. AN 2012-04 Revision History: date (12-04-20), V1.0 Previous Version: none st Subjects: 1 revision Authors: IFAT PMM APS SE SL René Mente Francesco Di Domenico We Listen to Your Comments Any information within this document that you feel is wrong, unclear or missing at all? Your feedback will help us to continuously improve the quality of this document. Please send your proposal (including a reference to this document) to: [[email protected]] 2 500V CoolMOSTM CE Application Note AN 2012-04 V1.0 April 2012 Table of contents 1 Introduction .................................................................................................................................................. 4 1.1 Features and Benefits ........................................................................................................................ 4 1.2 Applications (Target Market) .............................................................................................................. 5 2 Superjunction (SJ) Principle ...................................................................................................................... 5 2.1 General Description ........................................................................................................................... 5 2.2 Superjunction Benefit of 500V CE ..................................................................................................... 7 2.2.1 Switching Speed ............................................................................................................................ 7 2.2.2 BJT (Bipolar Junction Transistor)-Effect ........................................................................................ 9 3 Technology Parameters ............................................................................................................................11 3.1 Gate Charge (Qg) .............................................................................................................................11 3.2 Energy Stored in Output Capacitance (Eoss) ....................................................................................12 4 Measurement Results ...............................................................................................................................13 4.1 Efficiency in CCM PFC ....................................................................................................................13 4.2 Hard Commutation on Conducting Body Diode ...............................................................................15 5 Design Guideline for Using 500V CE .......................................................................................................16 5.1 Minimum External Gate Resistor (RG,ext) .........................................................................................16 5.2 Paralleling of 500V CE .....................................................................................................................16 5.3 Safe Operation after Protection Mode .............................................................................................17 6 Portfolio ......................................................................................................................................................19 7 References .................................................................................................................................................20 3 500V CoolMOSTM CE 1 Application Note AN 2012-04 V1.0 April 2012 Introduction TM The new CoolMOS CE is the fourth technology platform of Infineon’s market leading high voltage power MOSFETs designed according to the revolutionary superjunction (SJ) principle in the 500V class. 500V CE portfolio provides all benefits of a fast switching superjunction (SJ) MOSFET while keeping ease of use and implementation. The complete CE series of MOSFETs achieve very low conduction and switching losses, and can make applications more efficient, more compact, lighter and thermally cooler. This application note will describe the fundamental differences between a SJ MOSFET and a standard MOSFET. Additionally, all features and benefits impacting the target applications will be described. Furthermore, these features will be illustrated from both a theoretical point of view and in hardware TM measurements. It will also be shown that CoolMOS CE is a cost effective alternative compared to standard MOSFETs, which enables reaching higher efficiency levels while offering an attractive price/performance ratio. 1.1 Features and Benefits TM The following table represents the features and benefits of CoolMOS CE in comparison to standard MOSFETs, which will be discussed in depth in the main part of this application note. Table 1: features and benefits FEATURES BENEFITS Reduced energy stored in output capacitance (Eoss) Reduction of switching losses, improvement of light load efficiency High body diode ruggedness Higher reliability under critical operating conditions Reduced reverse recovery charge (Qrr) Lower possibility of hard commutation in resonant topologies Improvement in light load efficiency Reduced gate charge (Qg) Lower gate drive capability required Easy control of switching behavior Overall Features Outstanding reliability with proven TM CoolMOS quality 4 500V CoolMOSTM CE 1.2 Application Note AN 2012-04 V1.0 April 2012 Applications (Target Market) The following table represents the target applications and topologies for these new MOSFETs. Table 2: target applications and topologies APPLICATION PFC PC Silverbox Boost-Stage LCD/LED/PDP TV Boost-Stage Gaming Boost-Stage Lighting Boost-Stage PWM TTF LLC LLC TTF LLC LLC All the features and benefits of the 500V CE in connection with the target applications and topologies will be analyzed in section 4. The following section will describe the differences between SJ MOSFETs and standard MOSFETs. 2 Superjunction (SJ) Principle In the past the consumer market has been dominated by standard MOSFETs. Therefore this chapter is included to show the difference to SJ MOSFETs. 2.1 General Description TM “All CoolMOS series are based on the Superjunction principle, which is a revolutionary technology for high voltage power MOSFETs [1, 2], Infineon Technologies has been the first company worldwide to commercialize this idea into the market [4]. Where conventional power MOSFETs just command on one degree of freedom to master both on-state resistance and blocking voltage, the Superjunction principle allows two degrees of freedom for this task. Therefore conventional MOSFETs are stuck with the limit of silicon, a barrier which marks the optimum doping profile for a given voltage class. This limit line has been theoretically derived by Chen and Hu in the late 80ies [3]. No commercial product has an on-state resistance better than the limit line of silicon.” [5] Figure 1 represents the area-specific on-resistance versus breakdown voltage. 5 Area specific resistance [Ω*mm2] 500V CoolMOSTM CE Application Note AN 2012-04 V1.0 April 2012 40.00 30.00 20.00 State-of the-art conventional MOS 10.00 "Silicon limit" CoolMOSTM 0.00 500 600 700 800 900 1000 Blocking voltage [V] Figure 1: area-specific on-resistance versus breakdown voltage comparison of standard MOSFET and CoolMOS TM technology [6] “In contrast to that the Superjunction principle allows to reduce the on-state resistance of a high voltage MOSFET virtually to zero, limited only by technology efforts and manufacturing capabilities.” [5] “The basic idea is simple: instead of having electrons flowing through a relatively high resistive (high voltage blocking) n-area, we allow them to flow in a very rich doped n-area, which gives naturally a very low on-state resistance. The crucial point for the SJ technology is to make the device block its full voltage, which requires a careful balancing of the additional n-charge by adjacently positioned deep p-columns, which go all the way straight through the device close to the back side n+ contact. This is where manufacturing capability comes in, as the charges within the device need to be compensated precisely under the constraints of a mass market production line.” [5] Figure 2 shows the cross section of a standard MOSFET (left) and a SJ MOSFET (right). 6 500V CoolMOSTM CE Application Note AN 2012-04 V1.0 April 2012 Figure 2: cross section of standard MOSFET (left) and SJ MOSFET (right) [5] “The SJ principle gives us the opportunity to create best-in-class types, which have not been possible before such as a 100 mΩ/600V part in a TO-220 package. Furthermore it allows making parts with very low capacitances for a given RDS(on) as the silicon chip is much smaller than for a conventional power MOSFET. Both input and high voltage level of the output capacitance scale directly with the chip size, whereas reverse capacitance and to some extent the low voltage level of the output capacitance is technology dependent. Characteristic of all Superjunction devices is a strong non-linearity of the output capacitance with high values at low voltage and low values at high voltage. This behavior can be easily understood if you take into account that the output capacitance is proportional to the area of the blocking pn-junction and inverse proportional to the width of the space charge layer (or the voltage sustaining area). At low voltage the pcolumns are not depleted and form a very big surface, furthermore the width of the space charge layer is very narrow (the white area seen in” Figure 2). ” At high voltage however the p-columns are fully depleted and the space charge layer has reached its full extension of roughly 45μm for a 600V device. Important is that the non-linearity of the output capacitance allows a quasi zero-voltage-switching (ZVS) turn-off of the device, lowering turn-off losses. Superjunction devices are by nature fast in switching. Very small capacitances together with a low gate charge make rise and fall times of a few nanoseconds a reality.” [5] For more information on Superjunction devices please read the article “Mastering the Art of Slowness” which is available on www.infineon.com. 2.2 Superjunction Benefit of 500V CE Chapter 2.1 illustrated the general characteristics of a SJ MOSFET in comparison to a standard MOSFET. Now the question arises “What is the benefit for the 500V CE?” This application note will describe two of the most important factors starting with the switching speed. 2.2.1 Switching Speed As mentioned in the general description the switching speed increases dramatically. This behavior comes from the low parasitic capacitances of a SJ MOSFET in comparison to the standard MOSFET. A SJ MOSFET has about half of the value of input and output capacitance, which brings the benefits for switching losses and driving losses. Figure 3 represents these parasitic capacitances (marked in red) in a simplified schematic. 7 500V CoolMOSTM CE Application Note AN 2012-04 V1.0 April 2012 Figure 3: simplified small signal MOSFET equivalent circuit Because of this capacitance reduction the Eon and Eoff of the 500V CE is about half in comparison to a standard MOSFET. Furthermore this reduction of capacitances results also in a reduced gate charge Qg which gives the benefit of reduced driving losses, and the possibility to use a lower cost driver with less gate drive capability. Figure 4 represents the capacitance comparison of the 500V CE (280mOhm) vs. a comparable standard MOSFET. Capacitances IPA50R280CE vs. Standard MOSFET 10000 Ciss, Coss, Crss [pF] 1000 IPA50R280CE Ciss IPA50R280CE Coss 100 IPA50R280CE Crss standard MOS Ciss standard MOS Coss standard MOS Crss 10 1 0 100 200 300 400 500 VDS [V] Figure 4: capacitance comparison 500V CE vs. standard MOSFET 8 500V CoolMOSTM CE Application Note AN 2012-04 V1.0 April 2012 “A fundamental characteristic of all Superjunction devices is, that both the output and reverse capacitance show a strong non-linearity. The non-linearity in Superjunction capacitance characteristics comes from the fact that at a given voltage – typically in the range of 1/10th of the rated blocking voltage – p- and n-columns deplete each other leading to a fast expansion of the space charge layer throughout the structure. This means that at a voltage beyond 50V for 500V rated devices both output and reverse capacitance reach minimum values of a few pF only, resulting in a dv/dt of more than 100V/ns and di/dt of several thousand A/μs if the load current is allowed to fully commute into the output capacitance during turn-off. The output capacitance is charged up to the level of the bus voltage where the voltage rise follows then the formula: dv / dt I load C oss (1) The voltage rise is therefore proportional to the load current Iload and inverse proportional to the value of the output capacitance Coss. Because of the decreasing Coss towards higher voltages, the highest dv/dt is reached shortly before reaching the bus voltage. The according di/dt is mainly limited by the inductances of package and PCB circuit. The highest efficiency can now be reached by turning-off the device in this manner, because the occurring switching losses can be ideally reduced down to the level of the stored energy in the output capacitance.” [7] All these benefits will be clearly visible in the efficiency results, which will be described in chapter 4. The second difference is the so called BJT-Effect. 2.2.2 BJT (Bipolar Junction Transistor)-Effect If the body diode conducts in forward direction, minority carriers remaining in the base region during diode recovery can cause a BJT action with destructive results (short circuit of drain source while high voltages are applied). How is it possible to trigger the BJT-Effect? This is shown step by step in the following: In a zero voltage switching topology the forward current (ISD) is forced into the body diode to clamp the output at either the positive or negative rail following a current driven drain to source transition. This forward current causes the generation of minority carriers in both the p doped body (electrons) and nepi regions (holes). 9 500V CoolMOSTM CE Application Note AN 2012-04 V1.0 April 2012 The MOSFET channel is turned ON and diverts a portion of the current through the channel away from the body diode, that is still forward conducting (MOSFET can conduct current in both directions). This lower current flowing through the body diode will reduce the generation of minority carriers but will not stop it. The external circuitry reverses the current flow through the device -> small amount of reverse current flows in body diode (small due to the very weak voltage generated by very low current flowing in the low resistive channel, especially at light load operation). Some minority carriers will be removed from the p-n-junction, but not all due to a conduction period that is short in relation to the intrinsic carrier lifetime. If the MOSFET completely turns ON the current will be completely diverted to the channel, but if the MOSFET turns OFF when there are still minority carriers in the body diode the following happens: The MOSFET will begin to block voltage imposing a higher reverse voltage on the body diode, with high dv/dt. The application of high reverse voltage on the body diode will sweep the remaining carriers across the junction very quickly. Minority carriers in the nepi region are swept towards the p+ body. -> if this current (flowing into RB, represented in Figure 5) reaches a magnitude sufficient to activate the intrinsic bipolar transistor, second breakdown will occur destroying the MOSFET. In a conventional MOSFET the hole current, fed by reverse recovery charge, flow laterally into the p doped region crossing the area below the n region before they reach the top side of the device below the gate electrode: so this current flows through RB of the parasitic bipolar structure, with the risk of forward biasing of npn-junction and consequent triggering of parasitic BJT. 10 500V CoolMOSTM CE Application Note AN 2012-04 V1.0 April 2012 Figure 5: BJT-Effect TM As visible in Figure 5 (right) in a CoolMOS the hole current flows upwards through the p doped column, before it reaches the metalized contact, but no lateral current will pass through the p doped well and therefore no current flows through RB reducing the possibility of triggering the BJT-Effect to nearly zero. Now that the basics of the SJ MOSFET have been discussed, this paper is going to continue with technology parameters and their influence on the applications in the specific topologies. 3 Technology Parameters 3.1 Gate Charge (Qg) One of the most important improvements is the Q g reduction which brings benefits especially in light load conditions due to reduced driving losses. In general the 500V CE has about 40% Q g reduction in comparison to an comparable standard MOSFET over the whole R DS(on) range. Figure 6 shows the Qg in nC of the 500V CE against a standard MOSFET over the RDS(on),max range from 190mΩ to 950mΩ. 11 500V CoolMOSTM CE Application Note AN 2012-04 V1.0 April 2012 500V CE vs. Standard MOS typical Qg * RDS(on),max [nC*Ω] 350 300 Qg [nC] 250 200 ~40% Qg reduction 500V CE 150 standard MOS 100 50 0 0 200 400 600 800 1000 RDS(on),max [mΩ] Figure 6: Qg comparison 500V CE vs. standard MOSFET 3.2 Energy Stored in Output Capacitance (Eoss) The reduced energy stored in the output capacitance brings the most important difference in hard switching topologies but nevertheless it affects also the switching losses in a resonant topology. Normally it is possible to choose between zero voltage switching (ZVS) or zero current switching (ZCS). In these two cases it is possible to eliminate the turn-on losses (ZVS) or the turn-off losses (ZCS), but it is not possible to work in these two operation modes at the same time. Normally for MOSFETs the ZVS operation is preferred due to the usually important contribution of the output capacitance to the turn-on losses (if hard switching). Therefore, one part of the switching losses is still always in action and the reduction of Eoss brings a reduction of those switching losses. Figure 7 represents the Eoss comparison between the 500V CE and a comparable standard MOSFET of the 500mΩ devices. 12 500V CoolMOSTM CE Application Note AN 2012-04 V1.0 April 2012 IPP50R500CE vs. Standard MOS EOSS comparison of 500mOhm devices 10 9 8 IPP50R500CE EOSS [µJ] 7 6 standard MOS 5 4 3 2 1 0 0 100 200 300 400 500 600 VDS [V] Figure 7: Eoss comparison 500V CE vs. standard MOSFET The Eoss loss is in direct proportion to the output capacitance as a function of drain to source voltage of the MOSFET. In this case the effect of a reduction of Coss is clearly visible. One further benefit out of this is a faster VDS transition time in resonant topologies, which means that it is possible to reduce the resonant inductance and circulating current loss, because it is possible to completely discharge the Coss with lower currents. 4 Measurement Results In order to show the impact of the mentioned technology parameters this section will describe some measurements starting with the efficiency comparison in a CCM PFC, which is one of the most suitable topologies to verify the new MOSFETs in hard switching. 4.1 Efficiency in CCM PFC In this measurement the 500V CE is compared to a comparable standard MOSFET in the 280mΩ RDS(on) range. Setup parameters: CCM PFC Vin=90VAC Vout=400VDC Pout=0W to 400W Frequency=100kHz RG,ext=5Ω Ambient temperature 25°C Heat sink temperature preheated to 60°C Plug and play scenario between 500V CE and standard MOSFET 13 500V CoolMOSTM CE Application Note AN 2012-04 V1.0 April 2012 Figure 8: 500V CE vs. standard MOSFET comparison in absolute efficiency (upper) and delta efficiency (lower) This plug and play measurement shows the benefit of a SJ MOSFET in comparison to a standard MOSFET. In light load condition (~40W). Due to the Qg reduction an efficiency difference in light load operation (~40W) of more than 0.9% is visible. The efficiency of the IPP50R280CE is on average 0.4% higher than the comparable standard MOSFET over the whole load range. Here also the effects of the lower Eon and Eoff are visible. Figure 9 represents the Eon and Eoff values of an IPA50R500CE in comparison to a comparable standard MOSFET over RG,ext at different drain currents (ID) and test ambient temperature (TC) of 25°C. 14 500V CoolMOSTM CE Application Note AN 2012-04 V1.0 April 2012 Eoff - IPA50R500CE vs. Standard MOSFET Eon - IPA50R500CE vs. Standard MOSFET ID=2.93A; TC=25°C ID=2.93A; TC=25°C 14 12 Eon [µJ] Eoff [µJ] 10 8 6 IPA50R500CE 4 standard MOSFET 2 0 0 5 10 15 20 RG,ext [Ω] 25 30 20 18 16 14 12 10 8 6 4 2 0 35 IPA50R500CE standard MOSFET 0 5 10 15 20 RG,ext [Ω] 25 30 Eoff - IPA50R500CE vs. Standard MOSFET Eon - IPA50R500CE vs. Standard MOSFET ID=5.85A; TC=25°C ID=5.85A; TC=25°C 30 35 40 35 25 30 Eon [µJ] Eoff [µJ] 20 15 IPA50R500CE 10 20 15 IPA50R500CE 10 standard MOSFET 5 25 standard MOSFET 5 0 0 0 5 10 15 20 RG,ext [Ω] 25 30 35 0 5 10 15 20 RG,ext [Ω] 25 30 35 Figure 9: Eon and Eoff comparison IPA50R500CE vs. standard MOSFET at ID=2.93A (upper) and ID=5.85A (lower) It is shown that the Eon and Eoff are much lower on the 500V CE. Furthermore, it is visible that due to the differences in the Eoff behavior, it is possible to reduce the switching losses in comparison to the standard MOSFET both in hard switching DCM Mode PFC and soft switching/resonant topologies where the turn-off losses are dominant. Especially at higher loads it is visible that the reduction to for example 4Ω RG,ext brings you about 5µJ lower Eoff. 4.2 Hard Commutation on Conducting Body Diode Higher switching speeds could also cause drawbacks in case of, for example, high di/dt which could provoke high voltage peaks during hard commutation on a conducting body diode. The following figure represents this voltage peaks in comparison to a comparable standard MOSFET at hard commutation followed after 2µs body diode conduction time (under normal operation conditions you will not find longer body diode conduction times than 400ns). 15 500V CoolMOSTM CE Application Note AN 2012-04 V1.0 April 2012 IPP50R500CE vs. Standard MOS hard commutation on conducting body diode; half bridge configuration; high side MOS = low side MOS; same RG,sum=5Ω VDS,max, maximum VDS due to high dIrr/dt [V] 500 490 480 470 460 450 IPP50R500CE 440 standard MOS 430 420 410 400 0 1 2 3 4 5 6 7 IF, forward current through body diode [A] Figure 10: hard commutation on conduction body diode It is shown in Figure 10 that the maximum VDS has lower or the same values as the slower standard MOS. In other words the 500V CE has the same or, even better, behavior than the comparable standard MOSFET due to the self-limiting dv/dt behavior of this SJ MOSFET family. These two measurements and the technology parameters show that the 500V CE brings benefits in hard switching topologies and in soft switching topologies. The following chapter will represent an important design guideline for using these SJ MOSFETs. 5 Design Guideline for Using 500V CE 5.1 Minimum External Gate Resistor (RG,ext) The RG,int (internal gate resistor) is defined in the datasheets nevertheless it is recommended to use an RG,ext (external gate resistor) with a value higher than 2Ω. 5.2 Paralleling of 500V CE For paralleling 500V CE, the use of ferrite beads on the gate or separate totem poles is generally recommended. 16 500V CoolMOSTM CE 5.3 Application Note AN 2012-04 V1.0 April 2012 Safe Operation after Protection Mode This chapter is going to describe one design guideline which should be followed as a safety precaution. This guide should be followed when using the 500V CE in a LLC topology in combination with a controller with auto-restart after any kind of protection (over voltage protection (OVP), over current protection (OCP), over power protection (OPP), etc.). If the controller is used in the application with a complete latch-off protection (system has to be manually restarted) this guideline is not applicable. In order to provide safe operation the pause time between occurring of a protection state and auto-restart (in this document named as pause time tp_restart) should be set with respect to the following equation. t p _ restart Lr 5H t p _ restart Lr IS VF 0.5 I S VF s … pause time between occurring of protection state and auto-restart H A V … resonant inductance or leakage inductance of main transformer … continuous forward current of body diode … forward voltage of body diode (2) The following figure represents a simplified schematic that represents an LLC half bridge and the tp_restart in correspondence of the gate signal. 17 500V CoolMOSTM CE Application Note AN 2012-04 V1.0 April 2012 Figure 11: simplified circuitry for LLC half bridge and corresponding gate drive signal with autorestart TM Last but not least the next chapter is going to illustrate the 500V CoolMOS portfolio. 18 CE naming system and product 500V CoolMOSTM CE 6 Application Note AN 2012-04 V1.0 April 2012 Portfolio TM 500V CoolMOS CE series follows the same naming guidelines as already established with the CP series e.g. IPP50R500CE: I P P 50 R500 CE … … … … … … Infineon Technologies power MOSFET package type (TO-220) voltage class divided by 10 on-state resistance in milli Ohms name of the series Figure 12: portfolio 500V CoolMOS 19 TM CE series 500V CoolMOSTM CE Application Note AN 2012-04 V1.0 April 2012 7 References [1] T. Fujihira: “Theory of Semiconductor Superjunction Devices”, Jpn. J. Appl. Phys., Vol.36, pp. 62546262, 1997 A.W. Ludikhuize: “A review of the RESURF technology”, Proc. ISPSD 2000, pp. 11-18 X. B. Chen and C. Hu, “Optimum doping profile of power MOSFET’s epitaxial Layer.”, IEEE Trans. Electron Devices, vol. ED-29, pp. 985-987, 1982 G. Deboy, F. Dahlquist, T. Reiman and M. Scherf: “Latest generation of Superjunction power MOSFETs permits the use of hard-switching topologies for high power applications”, Proceedings of PCIM Nürnberg, 2005, pp. 38-40 TM G. Deboy, L. Lin, R. Wu: “CoolMOS C6 Mastering the Art of Slowness”, Application Note revision 1.0 2009-12-21, pp. 5-6 TM IFX: “CoolMOS 900V – New 900V class for superjunction devices – A new horizon for SMPS and renewable energy applications”, Application Note revision 1.0 2008-02, pp. 6, figure 1 Dr. H. Kapels: “Superjunction MOS devices – From device development towards system optimization”, paper EPE 2009 – Barcelona, ISBN 9789075815009, pp. 3 [2] [3] [4] [5] [6] [7] 20