[SI-LIST] Re: Bulk capacitor decoupling
- From: Istvan Novak <istvan.novak@xxxxxxx>
- To: Offir Assayag <Offir.Assayag@xxxxxxxxxxxx>
- Date: Sun, 28 Dec 2008 16:49:24 -0500
Hi Offir,
As always, the details depend on several of your input parameters, such
as transient current, maximum allowed noise, static tolerances, PDN
topology and PDN impedance synthesis type.
If I wanted to make a generic, approximate design for your case, I would
go for a Big-V impedance synthesis and assuming 1.5A transient current
and 150mVpp worst-case allowed noise. From these input numbers you
would need bulk capacitors with a cumulative ESR of around 30 mOhm.
Assuming a generic one-phase DC-DC converter, its closed-loop output
impedance may have an equivalent inductance of a microHenry. From these
you would need a total bulk capacitance of around 2200uF. Assuming that
the bulk capacitors have around 10nH inductance, you would also need at
least 10uF worth of ceramic capacitors. You mentioned 0.1uF ceramics
per pin. I assume you want to use 0402 size ceramics. Today you can
easily get 1uF in 0402 case size, so you may want to use ten of those.
Best regards,
Istvan Novak
SUN Microsystems
Offir Assayag wrote:
> Hi,
> i have a high speed digital IC which its internal frequency is 300Mhz &
> 800Mhz.
> Its core voltage is 1.2v with ~3A current consuption.
> I am debating on which bulk capacitors to add.
> I added 0.1uF capacitors on each VCC pin , but i want to know how to
> calculate
> which bulk capacitor should i add to it.
> Need help.
> Thanks!
> offir
>
>
>
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