[SI-LIST] Re: Decoupling at 800Mhz

Hi Stefan,
I quite agree with your point of view.
However, we usually can't get the details about the package information =
from
vendors to estimate the performance of it.
And vendors' design guides always conservative and redundant.
So a spec for PDN co-design simulation is being expected, just like IBIS
spec for SI simulation.=20

Best Regards,
Zhengrong

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=B4=FA=B1=ED Stefan Ludwig
=B7=A2=CB=CD=CA=B1=BC=E4: 2008=C4=EA5=D4=C224=C8=D5 17:35
=CA=D5=BC=FE=C8=CB: Subramanian R
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=D6=F7=CC=E2: [SI-LIST] Re: Decoupling at 800Mhz

Hi Mani,

if the processor runs at 800MHz, it doesn't mean that the decoupling=20
requirement for the PCB will be at 800MHz. Typically, the spikes at=20
800MHz will be taken care of by on-die capacitance.

As was said by others on this thread and you below, the mounting=20
inductance of the package on the board and the inductive path through=20
the package to the die will limit what you can do on the board. 1uF in=20
0402s as close to the power/gnd pins of the package, mounted with=20
vias-in-pad or vias to the side of the pads will be the best you can do=20
- in addition to having close spacing between pwr & gnd planes.=20
Typically, what you'll see on the board is in the range of 50-250MHz,=20
depending on how well the package is designed.

I hope this helps.

Cheers,

Stefan

Subramanian R wrote:
> Hi All,
> We are planning to use a processor running at 800 MHz.
> I was just reading up on the decoupling methods.
>
> The Processor PCB guidelines recommend using 1uF 0402 pack for high
> frequency decoupling. But at 800 MHz, will not the cap/package =
inductance
> dominate.
>
> The guideline doesn't say anything about plane decoupling also.
>
> Am I missing something? What are the best approaches for decoupling?
>
> Any suggestions will be very useful.
>
> Thank you in advance,
>
> Regards
> Mani
>  =20
--=20

Ludwig Systems Engineering         Consulting - Design - Implementation
WWW: www.ludwigsystems.com         System Architectures - FPGAs - PCBs
Ph/Fx: +41-43-355-58-73/74         Hardware - Firmware - Software

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