FreeLists / si-list / [SI-LIST] Re: PI Analysis about Core Power Supply

[Istvan Novak <istvan.novak@xxxxxxx>]

Dear Zhangkun,

As others suggested, your first line of attack is to request this data 
fromn
the chip vendor.

If you cannot get this data from the chip vendor, you are left with 
speculations.
 If you have the maximum current draw of the core, you can speculate about
the biggest transients it can create.  It could be relatively quiet, 
creating only a
small change in current, or it can vary widely, almost zero to 100%. 


If you want to save time and get a safe design the first time, you may 
need to
assume that the current can switch between zero and 100%.  There is always
some leakage, so the current will never go down to zero, plus the 
maximum is
dependent on process, temperature and voltage, unless you can sort out 
those
details before you have to design the PDN, the safe bet is just to use 
the extremes. 
This approach is more warranted as your frequency of interest goes down.
Even if fast transients in the core current are limited by proper core 
design,
'slow' transients, say in the microseconds or even millisecond range, will
most likely be a full 'minimum' to 'maximum' current swing.


Regards,
Istvan


Zhangkun wrote:

>Dear All
>In current work, I am studying core power supply. The voltage of core power is 
>very low (0.9V-1.2V) and the power consuming is very high (dozens of Amperes). 
>There is often power integrity problem in the frequency domain from 10MHz to 
>20MHz. The solution is very easy that discrete caps should be added on the PCB.
>
>My problem is that the PI problem is found out until the first edition has 
>been produced. Then the decoupling caps is determined. I want to determine the 
>decoupling caps before the first edition is produced in order to quicken the 
>design flow. Therefore, I should know the current noise source. I have been 
>looking for the paper about how to get the core power consuming in IEEE 
>electrical library. However, I have not found any useful paper.
>
>I hope I have express myself clear. Any advice is prefered.
>
>Best Regards
>
>Zhangkun
>2005.5.8
>
>  
>

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