Mosfet Models

Apr 21, 2009 3 Replies
A

I am trying to find the value of K for an IRFAC30 and IRFAC40 in this well known model: ID = K ( VGS - VP )^2 which is in the active region.



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I need this to predict the gate voltage swing in my design. I am having trouble finding enough information in the data sheets to do this. Also I was not able find a spice model for these in the file downloaded at:

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The gfs entry is not useful for this because (VG-VP) for this parameter is not given. Not even VG is.



I cannot infer if from the RDS(on) parameters because VGS for both of these is the same. Otherwise I might have been able to solve for the two unknowns VP and K with these two RDS(on) entries.



How is this supposed to be done? Can it be done?


To reply directly remove the sj. from my email address. This is a spam jammer.
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J

Didn't surf very hard, did you...

*$ .model IRFAC30 NMOS(Level=3 Gamma=0 Delta=0 Eta=0 Theta=0 Kappa=0.2 Vmax=0 Xj=0 + Tox=100n Uo=600 Phi=.6 Rs=8.178m Kp=20.5u W=.36 L=2u Vto=3.712 + Rd=1.848 Rds=2.667MEG Cbd=672.2p Pb=.8 Mj=.5 Fc=.5 Cgso=1.553n + Cgdo=140.9p Rg=.8118 Is=1.05n N=1 Tt=685n) * Int'l Rectifier pid=IRFCC30 case=TO3 * 88-08-26 bam creation *$ .model IRFAC40 NMOS(Level=3 Gamma=0 Delta=0 Eta=0 Theta=0 Kappa=0.2 Vmax=0 Xj=0 + Tox=100n Uo=600 Phi=.6 Rs=566.8u Kp=20.66u W=.66 L=2u Vto=3.513 + Rd=.9467 Rds=2.667MEG Cbd=1.33n Pb=.8 Mj=.5 Fc=.5 Cgso=1.668n + Cgdo=110p Rg=1.137 Is=124.5p N=1 Tt=795n) * Int'l Rectifier pid=IRFCC40 case=TO3 * 88-08-26 bam creation *$

You should have been able to fit your equation from the data sheet. Why couldn't you ?:-)

...Jim Thompson

| James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC\'s and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine Sometimes I even put it in the food
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A

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Where did you get this? In the downloaded zip file I expanded the file names in alphabetical order went from irf9956.spi to irfb31n20.spi.

After posting this I figured out that the current:

ID = K ( VGS - VP )^2

and the equation for transconductance, which is the derivative of the above is:

dID/dVGS = gfs = 2 K ( VGS - VP )

The two unknowns are ( VGS - VP ) and K. Knowns from the datasheet are ID and gfs. This can be solved for:

K = gfs^2/(4 ID );

To reply directly remove the sj. from my email address. This is a spam jammer.
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J

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[snip]

Not from where you looked ;-)

...Jim Thompson

| James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC\'s and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine Sometimes I even put it in the food
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