[SI-LIST] Re: SSN Vs Load cap

Upto the maximum current driving capability of driver, the increase in load 
capacitance causes
the current rate to increase and noise increases, so SSO index should reduce.
Once its reached the maximum drive capability at a particular load cap, the 
increase of cap
causes the rate of voltage to fall, as per the max. current spec. But since the 
current remains same (as the driver
cant supply more than that), I expect SSO index to be unchanged.
Equations :
i  = c. dv/dt
di/dt = c.(d2v/dt2) ....(its d square v by dt square)
sso noise = L.di/dt = L.c.(d2v/dt2).

Please clarify, if I'm missing anything.

Regards
Canes

----- Original Message ----
From: Sabyasachi Mohapatra <sabbu1981@xxxxxxxxxxx>
To: si-list@xxxxxxxxxxxxx
Sent: Thursday, February 1, 2007 6:13:12 PM
Subject: [SI-LIST] Re: SSN Vs Load cap

It is pretty simple.
as u increase the load cap with same drive strength of driver,
rise or fall slew will degrade.
As the buffers will be switching slower now, dI/dt will be less,
rate of change of current though package inductor will be less.
So less SSO noise.

--- In si-list@xxxxxxxxxxxxxxx, Canes Venatici <starsilic@...> wrote:
>
> Hi all,
> I couldn't understand why if load capacitance is increased, SSN is 
reduced (as the recommendation is increased SSO index, more signal 
pads can be accommodated by power pads).
> As di/dt is directly proportional to load cap, increasing the load 
causes more drop in parasitic inductance and SSN should increase.
> Could anyone clarify.
> Thanks,
> Canes
> 
> 
> 
> 
> 
> 
>  
> 
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