1 application considerations for sic mosfets january 2011 1 application considerations for silicon carbide mosf ets author: bob callanan, cree, inc. introduction : the silicon carbide (sic) mosfet has unique capabil ities that make it a superior switch when compared to its silicon counterparts. the advantages of sic mosfets have been documented extensively in the literature [1]. however, there are some unique ope rating characteristics that need to be understood s o that the device can be used to its full potential. discussion : the key to successfully applying the sic mosfet req uires an understanding of the device?s unique operating characteristics. in this section, the ch aracteristics of cree?s 1200v 80m sic mosfet (cmf20120d) will be discussed. comparisons will be made with other similar silicon devices along with application implications. the intention of this co mparison is to illustrate the differences in operat ing characteristics, not to pick the best device. the comparison silicon devices are as follows: ? 900v, 0.12 ? si super junction mosfet (sjmosfet) infineon ipw90 r120c3 [2] ? 1.2 kv, 20 a trench/field stop (tfs) si igbt fairc hild fga20n120fgd [3] ? 1.2 kv, 20 a non-punch though (npt) si igbt intern ational rectifier irgp20b120u [4] ? 1.2 kv, 0.30 ? si mosfet (si mos8) microsemi apt34m120j [5] the devices selected for comparison are representat ive of commercially available si igbts and mosfets with voltage and current ratings similar to the cmf20120d. the tfs igbt is representative of a low on-voltage device and the npt igbt is represe ntative of a low turn-off loss device. the si mos8 is representative of a commercially available 1.2kv si mosfet. lastly, although not a 1.2kv device, the 900v sjmosfet data was included for comparison purp oses. all comparisons were made with measured data except in the case of the sjmosfet. data sheet values were used. consider the output characteristics of a typical cr ee cmf20120d and the si tfs igbt shown in figure 1. for the cmf20120d, the transition from triode ( ohmic) to saturation (constant current) regions is not as clearly defined as it is for the si tfs igbt. t his is a result of the modest transconductance of t he device. the modest amount of transconductance caus es the transition from triode to saturation to be spread over a wider range of drain current. the re sult is that the cmf20120d behaves more like a voltage controlled resistance than a voltage contro lled current source. discussion introduction application considerations for silicon carbide mosfets bob callanan, cree inc CPWR-AN08, rev - application considerations for sic mosfets - january 2011 subject to change without notice. www.cree.com
2 application considerations for sic mosfets january 2011 CPWR-AN08, rev - application considerations for sic mosfets - january 2011 this document is provided for informational purposes only and is not a warranty or a specifcation. for product specifcations, please see the data sheets available at www.cree.com/power. for warranty information, please contact cree sales at powersales@cree.com. sic mosfet figure 1 : o the modest transconduct ance and short device. the cmf20120d needs to be driven with a higher gate voltage swing than what is customary with sjmosfets or igbts. presently, for the cmf20120d. care needs to be taken not to exceed of gate voltage will have a greater effect on the r ate of rise of the drain current due to the transconductance. therefore, the gate drive needs to supply a fast rise and fall time gate pulse to maximize switching speed. the cmf20120d (2v nominal). like the si sjmosfet, consideration especially at high temperatures. the rather large triode region can have active de- saturation circuits. some of these designs assume t impedance constant current and/or tran cmf20120d , the output impedance is lower and the region during this type of over- current fault drain to source voltage will not increase as much carefully considered in fault protection schemes. the forward conduction characteristics of the igbts are presented in figure 2. t r ds(on) has a considerable effect on its conduction losses. were somewhat similar. at 150 c, c to 150 c, whereas both the si sjmosfet and si mos8 devices significant effect on system thermal design. the o bvious advantage is that a smaller device can be us ed at higher operating temperatures. 2 si npt igbt : o utput characteristics comparison (t j = 150 c) ance and short - channel effects are important to consider when appl ying the needs to be driven with a higher gate voltage swing than what is customary with sjmosfets or igbts. presently, a +20v and -2v to -5v negative bias gate drive is recommended care needs to be taken not to exceed - 5v in the negative direction of gate voltage will have a greater effect on the r ate of rise of the drain current due to the transconductance. therefore, the gate drive needs to supply a fast rise and fall time gate pulse to cmf20120d also has a threshold voltage similar to the si sjmo sfet (2v nominal). like the si sjmosfet, consideration s need to be made for the lower threshold voltage, have an impact on certain types of fault detection schemes, chiefly the saturation circuits. some of these designs assume t hat the switching device enters a fairly high and/or tran sconductance saturation region during over- current , the output impedance is lower and the device does not go into a clean constant current current fault , especially under moderate over-currents . therefore, the not increase as much . these characteristics of the sic mosfet need carefully considered in fault protection schemes. the forward conduction characteristics of the cmf20120d along with the si sjmosfet, t he si sjmosfet?s relatively high positive temperature coefficient of considerable effect on its conduction losses. at 25 c, the si sjmosfet and the r ds(on) of the cmf20120d increases by only about 20% from 25 whereas both the si sjmosfet and si mos8 devices incre ase by 250%. significant effect on system thermal design. the o bvious advantage is that a smaller device can be us ed si npt igbt channel effects are important to consider when appl ying the needs to be driven with a higher gate voltage swing than what is customary gate drive is recommended 5v in the negative direction . the rate of rise of gate voltage will have a greater effect on the r ate of rise of the drain current due to the lower transconductance. therefore, the gate drive needs to supply a fast rise and fall time gate pulse to also has a threshold voltage similar to the si sjmo sfet s need to be made for the lower threshold voltage, impact on certain types of fault detection schemes, chiefly the hat the switching device enters a fairly high current faults. for the device does not go into a clean constant current . therefore, the . these characteristics of the sic mosfet need to be si sjmosfet, tfs, and npt temperature coefficient of si sjmosfet and cmf20120d only about 20% from 25 ase by 250%. this has a significant effect on system thermal design. the o bvious advantage is that a smaller device can be us ed
3 application considerations for sic mosfets january 2011 CPWR-AN08, rev - application considerations for sic mosfets - january 2011 this document is provided for informational purposes only and is not a warranty or a specifcation. for product specifcations, please see the data sheets available at www.cree.com/power. for warranty information, please contact cree sales at powersales@cree.com. t j = 25 c figure 2 : forward conduction characteristics one of the key advantages to sic is the high temper ature capability afforded by the wide bandgap. thi s is clearly reflected in the leakage current compari son at elevated temperature shown in figure 3. the cmf20120d has about 20x lower leakage current at 150 current increases dramatically, to the point where the device fails due to excess power dissipation. the cmf20120d leakage current is still acceptable devices. t j = 150 ?c figure 3: high temperature leakage current compari son as previously mentioned, the recommended gate drive voltage for the 5v negative bias . however, the amount of gate charge required to s witch the device is low. the 1e-7 1e-6 1e-5 1e-4 1e-3 1e-2 1e-1 0 200 400 600 i d , i c (a) v ds , v ce (v) 4 t j = 150 c : forward conduction characteristics comparison (v gs = 20v, v ge = 15v) one of the key advantages to sic is the high temper ature capability afforded by the wide bandgap. thi s is clearly reflected in the leakage current compari son at elevated temperature shown in figure 3. the has about 20x lower leakage current at 150 c. at 200 c, the si comparison parts leakage current increases dramatically, to the point where the device fails due to excess power dissipation. the leakage current is still acceptable at this temperature and is over 100x lower than the si t j = 200 ?c figure 3: high temperature leakage current compari son as previously mentioned, the recommended gate drive voltage for the cmf20120d is + . however, the amount of gate charge required to s witch the device is low. the 800 1000 1200 (v) tfs igbt = 15v) one of the key advantages to sic is the high temper ature capability afforded by the wide bandgap. thi s is clearly reflected in the leakage current compari son at elevated temperature shown in figure 3. the c, the si comparison parts leakage current increases dramatically, to the point where the device fails due to excess power dissipation. the over 100x lower than the si + 20v and -2v to - . however, the amount of gate charge required to s witch the device is low. the
4 application considerations for sic mosfets january 2011 CPWR-AN08, rev - application considerations for sic mosfets - january 2011 this document is provided for informational purposes only and is not a warranty or a specifcation. for product specifcations, please see the data sheets available at www.cree.com/power. for warranty information, please contact cree sales at powersales@cree.com. ramifications of the modestly higher gate voltage a nd lower gate charge can be reconciled by using the product of gate charge and gate voltage as a metric of gate energy. the comparison is shown in figure 4. even though the operating conditions are not exactl y matched, the results of this comparison show that the other devices. therefore, the higher voltage swing does not adversely affect requirements. the cmf20120d v gs is usually experienced with other gate controlled s ilicon devices. observed in typical silicon mosfets and igbts. onc e again, this is primarily due the mode transconductance. gate charge comparison figure 4 a popular figure of merit wh en comparing minimization of the figure of merit is an indicator of cmf20120d and the other si mosf 32.4 ? *nc . the figure of merit of the kv part whereas the si sjmosfet is rated at only 900 v. 5 ramifications of the modestly higher gate voltage a nd lower gate charge can be reconciled by using the product of gate charge and gate voltage as a metric of gate energy. the gate charge and gate energy even though the operating conditions are not exactl y matched, the results of this comparison show that the cmf20120d gate energy is comparable to or lower than the the higher voltage swing does not adversely affect gate drive power gs versus gate charge characteristics are somewhat dif ferent from what is usually experienced with other gate controlled s ilicon devices. the miller plateau is not as flat as observed in typical silicon mosfets and igbts. onc e again, this is primarily due the mode gate charge comparison gate energy comparison figure 4 : gate charge and energy comparison en comparing mosfets is the product of r ds(on) and total gate c of merit is an indicator of the superior part. a comparison between the and the other si mosf ets is shown in figure 5. the si sjmosfet h as a figure of merit of . the figure of merit of the cmf20120d is 7.12 ? *nc. furthermore, the cmf20120d sjmosfet is rated at only 900 v. 1.75 2.09 2.57 0 1 2 3 4 5 6 energy (j) ramifications of the modestly higher gate voltage a nd lower gate charge can be reconciled by using the gate charge and gate energy even though the operating conditions are not exactl y matched, the comparable to or lower than the gate drive power versus gate charge characteristics are somewhat dif ferent from what is not as flat as observed in typical silicon mosfets and igbts. onc e again, this is primarily due the mode st amount of gate energy comparison and total gate c harge [6]. a comparison between the as a figure of merit of cmf20120d is a 1.2 2.70 5.44 figure 5: qg*r ds(on) figure of merit comparison
5 application considerations for sic mosfets january 2011 CPWR-AN08, rev - application considerations for sic mosfets - january 2011 this document is provided for informational purposes only and is not a warranty or a specifcation. for product specifcations, please see the data sheets available at www.cree.com/power. for warranty information, please contact cree sales at powersales@cree.com. figure the inductive turn- off losses versus temperature of the igbts are shown in figure 6. the freewheeling diode schottky diode. the turn- off losses of the igbts are significantl strongly increase with temperature. this is due to the tail loss inherent with igbts. the npt igbt i s significantly better than the tfs igbt. however, t he npt igbt conduction losses are much higher than the cmf20102d. the tfs igbt conduction loss is lower than the the highest of the three. turn-off loss figure 6 : switching loss vs. temperature comparison (v to achieve fast switching time, the gate drive inte rconnections need to have minimum parasitics, especially inductance. this requires the gate driv er to be located as close as possible to the cmf20120d . care should be exercised to minimize or eliminat e r be achieved by selecting an appropriate external ga te resistor. certain amount of turn- off snubbing that reduces voltage overshoot and rin ging. as with any majority carrier device, the cmf20120d has no tail, so the amount of drain voltage oversho ot and parasitic ringing is noticeably higher. the higher ringing i s of concern because the lower transconductance a nd low threshold voltage of the cmf20120d di/dt can couple back to the gate circuit through a ny common gate/source inductance. connection for the gate drive is recommended, especially if the gate driver cannot b e located clos cmf20120d. ferrite beads (nickel - are helpful to minimize ringing while maintaining f ast switching time high value resistor (10k ) betwe en gate and source in order to prevent excessive fl oating of the gate during system power up propa gation delays. like any other power mosfet, the that has a 2.5 ? 2.7 v built- in voltage, but a to a si sjmosfet. use of this diode is not recomme nded due to its high forward drop. an exte schottky diode is suggested. cree?s c2d10120a is the recommended device until su ch time that a 247 single co-packag ed part is released. conclusions: 6 5: qg*r ds(on) figure of merit comparison off losses versus temperature of the cmf20120d compared with the tfs and npt the freewheeling diode used with all devices was a 1.2 kv, 10a sic off losses of the igbts are significantl y higher than the cmf20120d strongly increase with temperature. this is due to the tail loss inherent with igbts. the npt igbt i s significantly better than the tfs igbt. however, t he npt igbt conduction losses are much higher than the tfs igbt conduction loss is lower than the npt igbt , but the switching loss is turn-on loss : switching loss vs. temperature comparison (v dd = v cc = 800v, i d = i c = 20a, to achieve fast switching time, the gate drive inte rconnections need to have minimum parasitics, especially inductance. this requires the gate driv er to be located as close as possible to the . care should be exercised to minimize or eliminat e r inging in the gate drive circuit. this can be achieved by selecting an appropriate external ga te resistor. the silicon igbt current off snubbing that reduces voltage overshoot and rin ging. as with any majority has no tail, so the amount of drain voltage oversho ot and parasitic ringing is noticeably higher. the higher ringing i s of concern because the lower transconductance a nd of the cmf20120d reduces gate noise immunity. the high level of dra in current di/dt can couple back to the gate circuit through a ny common gate/source inductance. a kelvin recommended, especially if the gate driver cannot b e located clos - zinc recommended) in lieu of or in addition to an e xternal gate resistor are helpful to minimize ringing while maintaining f ast switching time . it is also recommended to connect a en gate and source in order to prevent excessive fl oating of the gate gation delays. power mosfet, the cmf20102d has a body diode. the body diode is a sic pn in voltage, but a substantially lower reverse recovery charge when co mpared to a si sjmosfet. use of this diode is not recomme nded due to its high forward drop. an exte cree?s c2d10120a is the recommended device until su ch time that a ed part is released. compared with the tfs and npt used with all devices was a 1.2 kv, 10a sic cmf20120d and strongly increase with temperature. this is due to the tail loss inherent with igbts. the npt igbt i s significantly better than the tfs igbt. however, t he npt igbt conduction losses are much higher than , but the switching loss is = 20a, r g = 10 ? ) to achieve fast switching time, the gate drive inte rconnections need to have minimum parasitics, especially inductance. this requires the gate driv er to be located as close as possible to the inging in the gate drive circuit. this can current tail provides a off snubbing that reduces voltage overshoot and rin ging. as with any majority has no tail, so the amount of drain voltage oversho ot and parasitic ringing is noticeably higher. the higher ringing i s of concern because the lower transconductance a nd reduces gate noise immunity. the high level of dra in current a kelvin recommended, especially if the gate driver cannot b e located clos e to the zinc recommended) in lieu of or in addition to an e xternal gate resistor it is also recommended to connect a en gate and source in order to prevent excessive fl oating of the gate is a sic pn diode substantially lower reverse recovery charge when co mpared to a si sjmosfet. use of this diode is not recomme nded due to its high forward drop. an exte rnal sic cree?s c2d10120a is the recommended device until su ch time that a to-
6 6 CPWR-AN08, rev - application considerations for sic mosfets - january 2011 copyright ? 2011 cree, inc. all rights reserved. the information in this document is subject to change without notice. cree, the cree logo, and zero recovery are registered trademarks of cree, inc. cree, inc. 4600 silicon drive durham, nc 27703 usa tel: +1.919.313.5300 fax: +1.919.313.5451 www.cree.com/power this document is provided for informational purposes only and is not a warranty or a specifcation. this product is currently available for evaluation and testing purposes only, and is provided as is without warranty. for preliminary, non-binding product specifcations, please see the preliminary data sheet available at www.cree.com/power. application considerations for sic mosfets january 2011 7 the cmf20120d has definite system advantages over c ompeting si switching devices. however, its unique operating characteristics need to be careful ly considered to fully realize these advantages. t he gate driver needs to be capable of providing +20v a nd -2v to -5v negative bias with minimum output impedance and high current capability. the parasit ics between the gate driver and the cmf20120d need to be minimized (close location, separate source re turn, etc.) to assure that the gate pulse has a fas t rise and fall time with good fidelity. the fast switchi ng speed of the cmf20120d can result in higher ring ing and voltage overshoots. the effects of parasitics in the high current paths need to be carefully asse ssed. references: [1] r. j. callanan, a. agarwal, a burk, m. das, b. hull, f. husna, a. powell, j. richmond, sei-hyung ryu, and q. zhang, ?recent progress in sic dmosfets and jbs diodes at cree?, ieee industrial electronics 34 th annual conference ? iecon 2008, pp 2885 ? 2890, 1 0 ? 13 nov. 2008, [2] infineon ipw90r120c3 coolmos datasheet, rev 1.0 , 2008-07-30. http://www.infineon.com/cms/en/product/findproductt ypebyname.html?q=ipw90r120c3 [3] fairchild fga20n120fgd datasheet, rev a, decemb er 2007 http://www.fairchildsemi.com/ds/fg%2ffga20n120ftd.p df [4] international rectifier irgp20b120u-e datasheet , pd-94117, 3/6/2001 http://www.irf.com/product- info/datasheets/data/irgp20b120u-e.pdf [5] microsemi apt34m120j datasheet, 050-8088 rev a , 2-2007 http://www.microsemi.com/datasheets/apt34m120j_a.pd f [6] f. bjoerk, j. handcock, and g. deboy, ?coolmost m cp ? how to make most beneficial use of the latest generation of super junction technology devi ces?, infineon application note an-coolmos-cp- 01, version 1.1, feb 2007. http://www.infineon.com/dgdl/aplication+note+coolmo s+cp+(+an_coolmos_cp_01_rev.+1.2).pdf ?folderid=db3a304412b407950112b408e8c90004&fileid=d b3a304412b407950112b40ac9a40688 summary
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