Re: [oc] Output loading in digital circuit

["Kenneth Hung" <hungwaiming@hotmail.com>]

It's just from the datasheet I am working on.
No application for me as it is a usual practice for
all companies like TI, FairChild, Phillips, IDT.
If you want, you might take a look at www.ti.com
and search PI74LVC245A part number and from
there you will see what I mean the loading circuit.

----- Original Message -----
From: "Steve Wilson" <stevew@intrinsix.com>
To: <cores@opencores.org>
Sent: Wednesday, April 03, 2002 4:35 AM
Subject: Re: [oc] Output loading in digital circuit


> I would have to see the application notes for the device to hazard a
guess.   What circuit in
> particular are you seeing this on?
>
> Steve Wilson
>
> Kenneth Hung wrote:
>
> > Hi Steve
> >
> > Ur answer might be correct in some sense in pF.
> > But do u know why there's an R=500 or R=1kohm in parallel
> > with the C ? I can't see no relation why there's a R and why is such
> > value ? For a typical transmission line, even the termination resistor
> > is 50ohm.
> >
> > ----- Original Message -----
> > From: "Steve Wilson" <stevew@intrinsix.com>
> > To: <cores@opencores.org>
> > Sent: Tuesday, April 02, 2002 4:19 AM
> > Subject: Re: [oc] Output loading in digital circuit
> >
> > > Let me try my hand at this - having designed boards in a past life.
> > >
> > > One thing you might be seeing is the "test circuit" that was used to
> > actually measure (or spice if
> > > you like) the timing numbers represented in the device data sheet.
They
> > have to quote something,
> > > so usually represent what that something is relative too.
> > > This allows you to scale your numbers if necessary OR use it as an
> > absolute load number you don't
> > > want to exceed in your own design.  Example: The test circuit had 50pf
in
> > it.  My design has 20 pf
> > > of load estimated on the board between the I/O's and board trace.  I'm
> > under their 50 pf number,
> > > so I should see the worst-case delay or better guaranteed.
> > >
> > > Does this help any?
> > >
> > > Steve
> > >
> > > --
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> > >
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