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

["Ihsan Erdin" <erdinih@xxxxxxxxx>]

Yu,

I'm guessing you're referring to the equation involving the 2nd time
derivative of current when you say it has no problem. No one here is
saying it has mathematically any problem but if you can explain the
physical meaning of the 2nd derivative of current wrt time you're
going to teach me something.

Regards

Ihsan

On 2/2/07, Yu Wang <wangy_km@xxxxxxxxx> wrote:
> 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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