[SI-LIST] Re: [!! SPAM] Re: 6 layers stackup

  • From: steve weir <weirsi@xxxxxxxxxx>
  • To: Joel Brown <joel@xxxxxxxxxx>
  • Date: Tue, 11 Mar 2008 11:13:18 -0700

Joel, you would scale the resistance and the number of resistors and/or 
total compensation networks to arrive at the inductance needed.  The 
method is disclosed in Istvan's patents.

Best Regards,


Steve
Joel Brown wrote:
> Istvan,
>
> Just a few qusetions regarding your comments:
>
> By adding discrete resistors do you mean add them in series with normal low
> ESR ceramic capacitors?
> If 0402 packages are used for both would the inductance be sufficiently low?
> I assume the higher ESR bypassing should be done as percentage of the total
> bypassing and should not be used to bypass local IC power pins?
>
> Thanks - Joel
>
>
>
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
> Behalf Of Istvan Novak
> Sent: Tuesday, March 11, 2008 6:04 AM
> To: steve weir
> Cc: Joel Brown; leeritchey@xxxxxxxxxxxxx; 'Scott McMorrow'; 'QU Perry';
> si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Re: [!! SPAM] Re: 6 layers stackup
>
> Joel,
>
> Just a few late comments to the thread (I was on vacation):
>
> - setting the resistance to dampen resonances is a useful thing to reduce
> worst-case transient noise and EMI risk.  For regular MLCCs this usually
> requires ESR values higher than what we get with a typical manufacturing
> process today.
>
> - in ceramic capacitors the required resistance can be created either by a
> smart internal construction (see the TDK announcement pointed out on the
> thread), or by adding resistance externally such as printed resistors (such
> as Sanmina's annual ring resistor) or by adding discrete resistor pieces
>
> - as it was mentioned, inductance is crucial: whether the resistance is
> added inside the MLCC or externally, we should not add too much inductance
> as it would defeat the purpose.  Fortunately each of the above three
> approaches can be implemented with sufficiently low inductance. 
>
> - for implementation options and simulated measured results you can see some
> of the published papers on the topic.  See for instance:
> "Overview of Some Options to Create Low-Q Controlled-ESR Bypass Capacitors"
> and "History of Controlled-ESR Capacitors at SUN" in TecForum TF-MP3
> "Controlled-ESR Bypass Capacitors Have Arrived" on
> http://home.att.net/~istvan.novak/papers.html
>
> Finally another comment on inductance: instead of setting the resistance to
> the optimum value, sufficiently low overall inductance of the bypass
> capacitors can also be used to reduce/eliminate resonances.  This is the
> rational (knowingly or unknowingly) behind the approach Charles mentioned
> (sprinkling the board with a lot of capacitors) and this is 
> the reason why lower inductance parts are always a welcome help.   
> However, from a design point of view we need to keep in mind that using a
> low cumulative inductance instead of the optimum resistance comes with a
> price: either the low-inductance parts are more expensive, or the
> low-inductance parts require more vias, or simply we need more parts.  
> Of course setting the resistance to the proper value has its own price tag
> as well, so eventually the design engineer has to make the decision which
> solution fits bets his/her requirements.  Typically in low-density and
> low-cost systems adding more capacitors works well; in high-density and/or
> high-performance systems selecting PDN components with the proper resistance
> becomes more attractive.
>
> Regards,
>
> Istvan novak
> SUN Microsystems
>
>
> steve weir wrote:
>   
>> Joel, controlled / high ESR caps are rare birds.  Istvan has been 
>> championing them for years nd some parts have been made.  If you are 
>> prepared to buy 100,000,000 at a shot you might get somewhere w/ the 
>> manufacturers.  But right now, most are running their lines to 
>> capacity w/ commodity parts.
>>
>> Regards,
>>
>>
>> Steve.
>> Joel Brown wrote:
>>   
>>     
>>> While we are all talking about bypass caps, I just got done reading a 
>>> book by Bruce Archambeault called "PCB Design for Real-World EMI 
>>> Control". In the book there is a chapter on bypassing and it shows 
>>> measurements from actual test boards. In one case, a certain percentage
>>>       
> of the caps are "high ESR"
>   
>>> which seems to result in substantial damping (reduction) of the
>>>       
> resonances.
>   
>>> The high ESR caps are described as ceramic capacitors with a series 
>>> resistor built into the package, I have been unable to find such a 
>>> part. Has anybody found a benefit to this approach and a source for high
>>>       
> ESR capacitors?
>   
>>> Thanks - Joel
>>>  
>>>
>>>
>>>
>>>   
>>>     
>>>       
>>   
>>     
>
>
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