I agree that this matrice will work in most instances and generally the engineer will make notation, if it is to be otherwise. Henry R. Linneweh PCB Designer On Fri, 5 Apr 1996, Waddell, Pete wrote: > > I've heard it said both ways. But what is the deal? Well since decoupling caps > are intended to minimize switching noise, which shows up at the pwr pin, what > we're trying to do is dump the noise to gnd. This means minimizing noise on > traces, so vcc trace(s) should be as short as possible. I've seen the Moto book > too and it confuses the hell out of a lot of people. Does the Moto fact book say > why the caps should be closer to gnd?? > > Theoretically the multi layer construction would seem to mean that since there > are no traces, (a surface mount cap does require a trace/via, however short, to > feed to the plane) the caps are filtering noise all across the board. Does this > make sense? > > Pete Waddell > > ______________________________ Reply Separator _________________________________ > Subject: Re: Placement of bypass caps > Author: [log in to unmask] at Internet > Date: 4/5/96 4:18 AM > > > Mr Brooks > The old rule of tumb was to set by-passes next to VCC so you did > not have a pwr trace running on top of your board the length of your > IC. > How ever today most boards have planes for pwr, gnd So a even > matrics of bypasses across the board will do the trick. > > All you are doing is decoupling vcc,gnd, if done correctly the board > and parts will not make noise. > > > > Hope this helps > DM PAVONE > Micros > > > ______________________________ Reply Separator _________________________________ > Subject: Placement of bypass caps > Author: [log in to unmask] at SMTPLINK-Micros > Date: 4/4/96 5:45 PM > > > I have several sources (including the Motorola FACT book) that say bypass > caps should be placed as close as possible to the GROUND pin of the IC (not > the power pin.) But I have seen few really specific discussions of why this > is so. > > Some of my customers insist on having them placed as close as possible to > the power pin. > > Can anyone give me a definitive explanation of where they should be placed, > and why? Thanks > > Doug Brooks > > > >