Low Rds(on) tempco
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From: Tim Williams on 24 Jan 2010 14:01 A little while ago, someone was asking if anyone makes MOSFETs with a low Rds(on) tempco. Fairchild is claiming an usually low ratio of ~1.63 = Rds(on)(175C) / Rds(on)(25C) for some low voltage FETs: http://www.fairchildsemi.com/ds/FD%2FFDP8860.pdf But they're also claiming 254W dissipation in a TO-220. Tempco of just the leads, in air, at rated current, is more than Fig.3 I'm pretty sure. Tim -- Deep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms
From: John Larkin on 24 Jan 2010 15:23 On Sun, 24 Jan 2010 13:01:28 -0600, "Tim Williams" <tmoranwms(a)charter.net> wrote: >A little while ago, someone was asking if anyone makes MOSFETs with a low >Rds(on) tempco. Fairchild is claiming an usually low ratio of ~1.63 = >Rds(on)(175C) / Rds(on)(25C) for some low voltage FETs: >http://www.fairchildsemi.com/ds/FD%2FFDP8860.pdf > >But they're also claiming 254W dissipation in a TO-220. Tempco of just the >leads, in air, at rated current, is more than Fig.3 I'm pretty sure. > >Tim Insane. 254 watts times 0.59 K/w is a 150K rise, and that's just the silicon to the case. The DC SOAR curve sure looks like 160 watts max to me. IR publishes absurd specs on their mosfets, too. It's hard to find a TO-247 that will dissipate an honest 250 watts. ftp://jjlarkin.lmi.net/ExFets.jpg John
From: Hammy on 24 Jan 2010 15:33 On Sun, 24 Jan 2010 13:01:28 -0600, "Tim Williams" <tmoranwms(a)charter.net> wrote: >A little while ago, someone was asking if anyone makes MOSFETs with a low >Rds(on) tempco. Fairchild is claiming an usually low ratio of ~1.63 = >Rds(on)(175C) / Rds(on)(25C) for some low voltage FETs: >http://www.fairchildsemi.com/ds/FD%2FFDP8860.pdf > >But they're also claiming 254W dissipation in a TO-220. Tempco of just the >leads, in air, at rated current, is more than Fig.3 I'm pretty sure. > >Tim Even Lower from TI their new CICLON line. http://focus.ti.com/lit/ds/symlink/csd25301w1015.pdf Full line up is here. http://focus.ti.com/general/docs/gencontent.tsp?contentId=53265&DCMP=ciclonannouncement&HQS=NotApplicable+OT+mosfet They sent me an email about them. They are nice for LV only 25VDS max; easy drive requirements as well. It's mainly the lower voltage ones that have the best tempco's. When you get up in higher voltage they are all usually about 1.8 to 2 x 25C. I'm sure I used to now why this is but forgot. Anything over 50VDS I just go at 2x 25C rdson to be safe.
From: Tim Williams on 24 Jan 2010 16:22 "Hammy" <spam(a)spam.com> wrote in message news:bjbpl51m0fv2p63c8dnt6v5v1sbd5cv4lh(a)4ax.com... > Even Lower from TI their new CICLON line. > http://focus.ti.com/lit/ds/symlink/csd25301w1015.pdf That is quite flat. 'Spose it helps not having leads, too. Average metal has an awful tempco. > They sent me an email about them. They are nice for LV only 25VDS max; > easy drive requirements as well. I spotted this phenomenon while exploring a low volt, high amp synchronous supply. I'm looking at things a bit harder to drive though (~200nC gate charge). :-) > It's mainly the lower voltage ones that have the best tempco's. When > you get up in higher voltage they are all usually about 1.8 to 2 x > 25C. I'm sure I used to now why this is but forgot. I would guess channel length. Something about short channel effects, or the way they have to build them when Vds(max) > Vgs(max)? I wonder, does anyone know what the typical feature size is for power MOSFETs? Still micrometers as usual? Anything gained from teensy sizes? Reminds me of an idle thought I had the other day... just imagine, if you took all the transistors on one of those big pigfucker FPGAs and put them all in parallel. You'd only get maybe 1.5Vds(max), but think of the amperage and switching speed. ;-) Tim -- Deep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms
From: Jan Panteltje on 24 Jan 2010 17:21
On a sunny day (Sun, 24 Jan 2010 12:23:13 -0800) it happened John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote in <qbapl5de5rq11soeieo5qoe7hel7hemcjs(a)4ax.com>: >On Sun, 24 Jan 2010 13:01:28 -0600, "Tim Williams" ><tmoranwms(a)charter.net> wrote: > >>A little while ago, someone was asking if anyone makes MOSFETs with a low >>Rds(on) tempco. Fairchild is claiming an usually low ratio of ~1.63 = >>Rds(on)(175C) / Rds(on)(25C) for some low voltage FETs: >>http://www.fairchildsemi.com/ds/FD%2FFDP8860.pdf >> >>But they're also claiming 254W dissipation in a TO-220. Tempco of just the >>leads, in air, at rated current, is more than Fig.3 I'm pretty sure. >> >>Tim > >Insane. 254 watts times 0.59 K/w is a 150K rise, and that's just the >silicon to the case. The DC SOAR curve sure looks like 160 watts max >to me. > >IR publishes absurd specs on their mosfets, too. > >It's hard to find a TO-247 that will dissipate an honest 250 watts. > >ftp://jjlarkin.lmi.net/ExFets.jpg > >John How cruel :-) |