[SI-LIST] Re: Power Integrity Question

  • From: steve weir <weirsi@xxxxxxxxxx>
  • To: Jerry Johnson <gerald.johnson@xxxxxxxxxxxx>
  • Date: Thu, 06 Nov 2008 06:51:07 -0800

Jerry, while the TDK caps look like X2Y's the dimensions and pad layouts 
are quite different.  At 0.1mm width the end terminals on the TDK parts 
are scary narrow.  If you are buying a lot of them, I would feed back 
your legitimate manufacturing concerns to TDK.

Steve.

Jerry Johnson wrote:
>  You can get them from Digi-Key overnight.
> They seem to work great, but we had to change our PCB
> footprint. The dimensional specifications on the width
> and placement of the side contacts are really loose, so
> you need narrow pads on the end caps to avoid potential
> shorts. That could open the door to tombstoning during
> assembly. Sure wish those dimensional specs were tighter.
>
> Jerry
>
> steve weir wrote: They're in their catalog. I haven't seen any though. Steve
> Peterson, James F (EHCOE) wrote: (follow-up to Steve's comments on Q)
> Whatever happened to the technique that TDK came up with a couple years back
> where they were purposely increasing a capacitor's ESR to reduce Q (and thus
> the large peaks mentioned in this thread)? I remember seeing it a few
> DesignCons ago - it seemed like such a great idea... Jim. -----Original
> Message----- From: si-list-bounce@xxxxxxxxxxxxx[1]
> [mailto:si-list-bounce@xxxxxxxxxxxxx[2]] On Behalf Of steve weir Sent:
> Thursday, November 06, 2008 8:07 AM To: Avtaar Singh Cc:
> si-list@xxxxxxxxxxxxx[3] Subject: [SI-LIST] Re: Power Integrity Question The
> simulators are reporting correctly. Your understanding of physics theory (
> actually Calculus ) is incorrect. A convenient way to think about the
> impedance anywhere is as a result of the characteristic impedance and the Q.
> In the original case, the impedance significantly away from the original
> poleapproximates the characteristic impedance. At each of the two peaks,
> whenthe impedance is reactive, Q >1, and the peak impedance is substantially
> greater than the characteristic impedance. Therefore if you've got peaks at
> all the impedance will always be above the original curve surrounding each
> one. Steve. Avtaar Singh wrote: Dear All: I have a very basic Power
> Integrityquestion. Lets say a Power Delivery Network (PDN) has an impedance
> peak at 100MHz. I add a capacitor that dips the impedance exactly at 100
> MHz,and creates 2 smaller peaks at, lets say, 20 MHz and 250 MHz. According
> to the theories of Physics, these peaks should have their impedance value
> little bit lesser than the impedance value of the PDN, at those 2 frequency
> points, before this capacitor was added. But we do not always see that in
> simulation tools. Sometimes we see that the 2 peaks that are formed have
> higher impedance than the impedance that existed at those frequency points
> before this last capacitor was added. This seems weird to me, because even
> though the ESR of the caps should decide how sharp or blunt the Z peaks are,
> but an added Z in parallel should always mean lesser impedance rather than
> more impedance. Can someone please explain this paradox? Thanks for the kind
> guidance. Regards, Avtaar Singh
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