[SI-LIST] Re: Ground bounce (was VOH datasheet question)
- From: dav0 <david.lieby@xxxxxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Tue, 14 Mar 2006 08:17:28 -0800
On top of everything else, a lot of larger packages have on-chip
decoupling capacitors. These provide a fixed amount of charge to
dump into the system. Adding more capacitance to the load will
cause a little more SSO.
Regards,
David Lieby
Andrew Ingraham wrote:
>>Is the turn-on time for a driver slow rather than instantaneous?
>
>
> Yes. Drivers don't turn on instantaneously. It's a combination of on-die
> and package effects. If you measure turn-on time or slew rate with a
> resistive load, you don't get zero or infinity.
>
> Increasing the load capacitance increases the area of the current pulse;
> that's all you can say for sure. Some of it is by lengthening the pulse's
> width, but also the amplitude may be somewhat larger because it doesn't
> instantaneously go to the short-circuit value. In any event, over a range
> of typical load capacitances, there is also interaction between the pulse
> duration and package impedances, such that the pulsewidth also figures into
> the amount of ground bounce you get (if the load capacitance is not so large
> that the width greatly exceeds the package time constants).
>
> Regards,
> Andy
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