Re: [SI-LIST] : Transmission line inductance

Dr. John L. Prince, III (prince@ece.arizona.edu)
Thu, 25 Mar 1999 12:17:00 -0700 (MST)

>I would like to now if anyone of you had to create a PCB trace with a
>precise inductance value?
>
>In the spec for LT1533 (Linear Technology switching regulator) is shown
>that
>the device should have 25nH inductance between the ground pin and the
>PCB
>GND. According to my calculations a microstrip line with W=7 (H=5, T=2.8
>and
>Er=4.3) has app. 6.5nH/inch. So to get a 25nH trace one would need to
>have a
>3.8inch long trace.
>
>Q1: Is there a trace configuration that I could use to create a 25nH
>inductance that would not be so lengthy and in the same time would not
>act
>as an antenna?
>
>Q2: Is my calculation (app 6.5nH/inch) correct?
>
>Josip
>
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I don't believe that your technique will work (although it is imaginative)
because the normal TL inductance is a loop inductance, not a partial
inductance. I have tried to imagine the application and I can't see the
role of the return current in your case. Perhaps I am not properly
visualizing the actual circuit. John Prince

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