IR is insane
in [Design]
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From: John Fields on 19 Mar 2010 12:26 On Fri, 19 Mar 2010 07:19:50 -0700, John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >On Thu, 18 Mar 2010 23:32:24 -0700, Muzaffer Kal <kal(a)dspia.com> >wrote: > >>On Thu, 18 Mar 2010 15:58:08 -0700, John Larkin >><jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >> >>>Just got a short-form IR mosfet thing in the mail. >>> >>>They have a PQFN 5x6 mm package they rate at 104 amps. And a D2PAK >>>rated for 340 amps. >>> >>>John >> >>The only thing that actually matters is whether you can stay under the >>power curve of I^2*Rdson(T). At 1milliohm max 340 Amps gives you 115 >>W. You need to make sure to check the C/W rating of the package and >>cool it enough. > >Rds-on is spec'd as 2.5 mohms max at 170 amps, and will go up at >higher currents as it self-heats. 340 amps would fuse the source lead. > >There's no practical way to heatsink a D2PAK to dissipate 375 watts. --- Well, since the spec reads 375W @Tc = 25C, if you're running it in an ambient of 25C, there's _no_ way. However, what's not practical for you might be eminently practical for someone else who's willing to use, say, chilled water. Then, of course, there's always derating and using multiple devices. JF
From: John Larkin on 19 Mar 2010 12:35 On Fri, 19 Mar 2010 11:26:56 -0500, John Fields <jfields(a)austininstruments.com> wrote: >On Fri, 19 Mar 2010 07:19:50 -0700, John Larkin ><jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: > >>On Thu, 18 Mar 2010 23:32:24 -0700, Muzaffer Kal <kal(a)dspia.com> >>wrote: >> >>>On Thu, 18 Mar 2010 15:58:08 -0700, John Larkin >>><jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >>> >>>>Just got a short-form IR mosfet thing in the mail. >>>> >>>>They have a PQFN 5x6 mm package they rate at 104 amps. And a D2PAK >>>>rated for 340 amps. >>>> >>>>John >>> >>>The only thing that actually matters is whether you can stay under the >>>power curve of I^2*Rdson(T). At 1milliohm max 340 Amps gives you 115 >>>W. You need to make sure to check the C/W rating of the package and >>>cool it enough. >> >>Rds-on is spec'd as 2.5 mohms max at 170 amps, and will go up at >>higher currents as it self-heats. 340 amps would fuse the source lead. >> >>There's no practical way to heatsink a D2PAK to dissipate 375 watts. > >--- >Well, since the spec reads 375W @Tc = 25C, if you're running it in an >ambient of 25C, there's _no_ way. > >However, what's not practical for you might be eminently practical for >someone else who's willing to use, say, chilled water. > Chilled water to cool a tiny surface-mount package? This uses TO247 packages, clamped to a gold-plated, water-cooled copper block, at those sorts of power levels. But the lead current is a lot lower than 340 amps. http://www.highlandtechnology.com/DSS/T220DS.html John
From: Joerg on 19 Mar 2010 12:58 langwadt(a)fonz.dk wrote: > On 18 Mar., 23:58, John Larkin > <jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: >> Just got a short-form IR mosfet thing in the mail. >> >> They have a PQFN 5x6 mm package they rate at 104 amps. And a D2PAK >> rated for 340 amps. >> >> John > > think this has part of the long explanation as to how the come up with > the numbers > > > http://www.datasheetarchive.com/pdf/Datasheet-076/DSAE0035054.pdf > Quote "To actually utilize our parts in an application that targeted currents at the level of the ultimate current would likely be costly and impractical. Nucleated boiling is an expensive and tricky proposition." ... and ... Quote "The heritage fleet of power MOSFET products has been rated via the classic method as described by equation 1. Those ratings fall on a very conservative engineering side. Newer, advanced products like the expanding suite of IR Trench products will begin carrying the new ultimate current limits, if appropriate." Why does this remind me of the real estate market? I want heritage datasheets :-) -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
From: Joerg on 19 Mar 2010 13:33 John Larkin wrote: > On Thu, 18 Mar 2010 23:44:48 -0700 (PDT), George Herold > <ggherold(a)gmail.com> wrote: > >> On Mar 18, 8:19 pm, John Larkin >> <jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: >>> On Thu, 18 Mar 2010 18:02:27 -0500, Damon Hill >>> >>> <damon16...(a)comcast.not> wrote: >>>> John Larkin <jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote in >>>> news:cpb5q5p2013r34ainnmcrdfjml4ifvp03g(a)4ax.com: >>>>> Just got a short-form IR mosfet thing in the mail. >>>>> They have a PQFN 5x6 mm package they rate at 104 amps. And a D2PAK >>>>> rated for 340 amps. >>>> Hmm. Define 'continuous'. (a >very< short pulse rating I'd believe) >>> The flyer doesn't mention pulsing. The D2PAK datasheet pulsed current >>> rating is 1080 amps. >>> >>> http://www.irf.com/product-info/datasheets/data/irfs3006pbf.pdf >>> >>> The flyer claims 340 amps. The datasheet says 270 amps but "package >>> limited" to 195. I don't believe any of them. >>> >>> The datasheet also claims 375 watts power dissipation... in a D2PAK! >>> >>> John >> I wonder if they are dunking it and it's heatsink into liquid >> nitrogen. One figure in the data sheet showed the on resistance as a >> function of temperature. The minimum temp was -60 C with a current of >> 175 Amps. >> >> George H. > > 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. > It seems "normal" these days. Take a look at this datasheet as an example, just came up in Raveninghorde's thread: http://www.fairchildsemi.com/ds/FA%2FFAN3100C.pdf Here you have a driver that is touted as 2A, 3A peak. The figures in the datasheet are of little use, not output loading curves and the table data has a wee remark that the device sits at VDD/2 when sinking 2.5A, sourcing is even worse. Easily overlooked. A young engineer might exclaim "hooray!" and design it in, only to have it almost unsolder itself or going *PHUT*. Then after a few experiences like that he might think that analog is a frustrating business to be in and move on to other fields :-( "Modern" datasheets can often only be used when reading between the lines and applying a healthy marketing hype correction factor. -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
From: John Larkin on 19 Mar 2010 14:29
On Thu, 18 Mar 2010 23:02:19 -0500, "Tim Williams" <tmoranwms(a)charter.net> wrote: ><a7yvm109gf5d1(a)netzero.com> wrote in message >news:41cb68b6-1386-4953-9cfa-21bc6c6582c4(a)l25g2000yqd.googlegroups.com... >> Wiki claims "hundreds of amps" for the secondary of the transformer >> inside those Weller soldering guns. >> So you got an easy source of amps there. Seems to me if the >> constriction in the copper bar that serves as the iron element gets >> hot, those tiny pins should get hot too? > >But nobody uses their soldering iron while submerged in nucleated boiling >fluid. The IR testing context isn't 100% clear to me, but using boiling liquid may be the way they get the DPAK source lead to not melt at their specified currents. Ditto not melting their solder joints to a pc board. John |