IR is insane
in [Design]
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From: krw on 23 Mar 2010 20:59 On Tue, 23 Mar 2010 17:54:56 -0700, John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >On Tue, 23 Mar 2010 19:29:32 -0500, "krw(a)att.bizzzzzzzzzzzz" ><krw(a)att.bizzzzzzzzzzzz> wrote: > >>On Tue, 23 Mar 2010 07:06:37 -0700, Archimedes' Lever >><OneBigLever(a)InfiniteSeries.Org> wrote: >> >>>On Mon, 22 Mar 2010 22:45:30 -0700, "JosephKK"<quiettechblue(a)yahoo.com> >>>wrote: >>> >>>>On Sun, 21 Mar 2010 17:42:34 -0500, "krw(a)att.bizzzzzzzzzzzz" <krw(a)att.bizzzzzzzzzzzz> wrote: >>>> >>>>>On Sun, 21 Mar 2010 10:43:02 -0700, "JosephKK"<quiettechblue(a)yahoo.com> wrote: >>>>> >>>>>>On Sat, 20 Mar 2010 18:09:39 -0500, "krw(a)att.bizzzzzzzzzzzz" <krw(a)att.bizzzzzzzzzzzz> wrote: >>>>>> >>>>>>>On Sat, 20 Mar 2010 12:12:14 -0700, Archimedes' Lever >>>>>>><OneBigLever(a)InfiniteSeries.Org> wrote: >>>>>>> >>>>>>>>On Sat, 20 Mar 2010 10:56:18 -0700, John Larkin >>>>>>>><jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >>>>>>>> >>>>>>>>>Boiling liquid carries away far more heat than still or even flowing >>>>>>>>>liquid. Since IR cheats as hard as they can, we can assume they used >>>>>>>>>boiling liquid. I fact, they say so. >>>>>>>> >>>>>>>> >>>>>>>> Chilled fluorinert does not need to be boiling to have thermal >>>>>>>>efficiency. >>>>>>> >>>>>>>Wrong again, AlwaysWrong. How do you think Fluorinert works? By magic? >>>>>> >>>>>>While i have seen Flourinert cooling maybe half a dozen times, only once was >>>>>>it used in phase change mode. I mostly saw circulated chilled liquid baths. >>>>>>Works real good for temperature stabilizing standard resistors. >>>>> >>>>>*Every* time I've seen it used there was a phase change somewhere in the >>>>>process. There are a *lot* of cheaper and better alternatives if a lowish >>>>>temper phase change isn't needed. Fluorinert doesn't have a stellar specific >>>>>heat. >>>> >>>>At which point i have to ask, was it Flourinert or just some refrigerant. >>>>See: >>>> >>>>http://en.wikipedia.org/wiki/Fluorinert >>>> >>>>http://products3.3m.com/catalog/us/en001/oil_gas/specialty_materials/node_HX0DNRHXKWge/root_GST1T4S9TCgv/vroot_G1F6DNZDBVge/theme_us_oilgas_3_0/command_AbcPageHandler/output_html >>> >>> >>> The idiot was thinking of a CFC. >> >>AlwaysWrong is *ALWAYS* wrong. > >You've gotta admire him for his dedication. You certainly did a good job of naming.
From: John Fields on 23 Mar 2010 21:16 On Mon, 22 Mar 2010 22:28:05 -0700, "JosephKK"<quiettechblue(a)yahoo.com> wrote: >On Mon, 22 Mar 2010 09:35:30 -0500, John Fields <jfields(a)austininstruments.com> wrote: > >>On Sun, 21 Mar 2010 10:14:57 -0700, "JosephKK"<quiettechblue(a)yahoo.com> >>wrote: >> >>>On Fri, 19 Mar 2010 11:05:14 -0500, John Fields <jfields(a)austininstruments.com> wrote: >>> >>>>On Fri, 19 Mar 2010 07:16:29 -0700, John Larkin >>>><jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >> >> >>>>>IR does insane things. The flyer I got spec'd the max current (340 >>>>>amps!) and Rds-on different from the part datasheet (270 amps, or 195 >>>>>amps "package limited")... all or which are preposterous for a dpak. >>>>> >>>>>When people play games like that, I don't buy their parts. >>>> >>>>--- >>>>Oh, well, it's your loss... >>>> >>>>60Vdss, Rds(on)max 2.5milliohms, 375 watts @25C Tc, it's a nice part. >>>> >>>>JF >>> >>>Well JF, what is the typical theta(jc) of a dpak? >> >>--- >>For IR, about 4K/W. >>--- >> >>>This sounds like a really crazy infinite heat sink driven by LN2. >> >>--- >>Could be, but if you're not willing to go to those extremes and you want >>to use it "conventionally" it's still not a bad part, huh? >> >>JF > >I certainly might, though companies that use specsmanship that radically >do not inspire my trust. Plus i hate fighting through datasheet gibberish >to get realistic properties; which gibberish, when detected, will almost >always make me change vendors. I do not want to spend the time to get >past obvious baloney to find out what the part can do in normal use. --- I don't disagree, But in their already cited application note IR addressed the "specsmanship" issue rather candidly, I thought, and also gave their reasons for using their approach to determining the balls-to-the-wall capabilities of the MOSFETs tested that way. Being aware of that, all the data required to operate the devices in more conventional ways is presented in the data sheet, so I don't see their "SuperSpec" being a problem, especially since the application note is referenced in the data sheet. Plus, I like IR. :-) JF
From: Don Klipstein on 23 Mar 2010 23:59
In <o7piq59d3fped4c8lisho18vfmo0jrv7rk(a)4ax.com>, John Fields wrote: (as I repeat after editing for space and line count): >On Mon, 22 3/10 22:28 -0700, "JosephKK"<quiettechblue(a)yahoo.com> said: >>On 22 3/10 09:35 -0500, John Fields <jfields(a)austininstruments.com> said: >>>On 21 Mar 2010 10:14 -0700, "JosephKK"<quiettechblue(a)yahoo.com> wrote: >>>>On 19 3/10 11:05 -0500, J Fields <jfields(a)austininstruments.com> said: >>>>>On 19 3/10 07:16 -0700, John Larkin wrote: >>>>>>IR does insane things. The flyer I got spec'd the max current (340 >>>>>>amps!) and Rds-on different from the part datasheet (270 amps, or 195 >>>>>>amps "package limited")... all or which are preposterous for a dpak. >>>>>> >>>>>>When people play games like that, I don't buy their parts. >>>>>Oh, well, it's your loss... >>>>> >>>>>60Vdss, Rds(on)max 2.5milliohms, 375 watts @25C Tc, it's a nice part. >>>> >>>>Well JF, what is the typical theta(jc) of a dpak? >>>--- >>>For IR, about 4K/W. >>>--- >>>>This sounds like a really crazy infinite heat sink driven by LN2. >>>--- >>>Could be, but if you're not willing to go to those extremes and you want >>>to use it "conventionally" it's still not a bad part, huh? >> >>I certainly might, though companies that use specsmanship that radically >>do not inspire my trust. Plus i hate fighting through datasheet gibberish >>to get realistic properties; which gibberish, when detected, will almost >>always make me change vendors. I do not want to spend the time to get >>past obvious baloney to find out what the part can do in normal use. >--- >I don't disagree, But in their already cited application note IR >addressed the "specsmanship" issue rather candidly, I thought, and also >gave their reasons for using their approach to determining the >balls-to-the-wall capabilities of the MOSFETs tested that way. > >Being aware of that, all the data required to operate the devices in >more conventional ways is presented in the data sheet, so I don't see >their "SuperSpec" being a problem, especially since the application note >is referenced in the data sheet. > >Plus, I like IR. :-) How about using the 100 or 125 C relevant junction temperature figure of Rds(on), preferably the 125C one that I have previously cited (and have difficulty remembering better than 4.2 milliohms or whatever), and considering that such case temperature (close enough to junction temperature in this case) is good for about 3-4 watts in a reasonable FR4 PCB design with 1 square inch of heatsinking copper on both sides of a 2-layer PCB with a "reasonable" wide-spreading heatsinking copper layout with reasonable deployment of themal vias. At this moment, I am getting into a mood to calculate 4 watts from 4 milli-ohms. That is amps being square root of 1,000, as in 31.6. Although I am in a good mood to approve 35-36 amps for a fairly aggressive version of a FR4/"conventional" PCB with wide copper heatsinking area and *heavy* deployment of appropriate thermal vias. I give a slight chance that 40-50 amps can be designed for reasonably on such a scheme. With metal core PCB, I don't have a problem with 80 to possibly 100-plus amps as long as *everything gets worked out*. I seem to think maximum of ballpark of 70-80 amps RMS even on MCPCB unless "beefing up" the high current path every couple millimeters of the way, including the narrow portion of the "source lead" of the MOSFET. I would hope that 4-5 mm trace width on MCPCB is sufficient for survivability and conductivity and sufficiently low voltage drop when conducting near or over 50 amps! - Don Klipstein (don(a)misty.com) |