FreeLists / si-list / [SI-LIST] Re: SSN Vs Load cap

[Yu Wang <wangy_km@xxxxxxxxx>]

Ihsan & Canes,
To my knowledge of physics and math, Canes's equation
has no problem. However, the equation is a classic
boundary problem which means the solution of equation
is very dependent on the start status and boundary
conditions.  so di/dt can be more or less. In general,
because of the driving capability of the driver is
limited, so increasing C can make di/dt smaller. 

Regards,
Yu


--- Ihsan Erdin <erdinih@xxxxxxxxx> wrote:

> Canes,
> 
> Sabayachi's explanation is plain and accurate.
> i=Cdv/dt is a lumped
> approximation to Maxwell-ampere eq.; so is v=Ldi/dt
> to
> Maxwell-Faraday. As such, both have physical
> connotations. Your
> di/dt=Cdv2/dt2 is mathematically correct but doesn't
> have any useful
> physical connotations.
> 
> Regards
> 
> Ihsan
> 
> On 2/2/07, Canes Venatici <starsilic@xxxxxxxxx>
> wrote:
> > 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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