NNTP-Posting-Date: Fri, 25 Oct 2002 22:57:19 -0500
From: "Dave VanHorn"
References: <3DB96152.1393B701@rica.net> <3DB9800A.780B223E@rica.net> <3DB9C8F4.5A42BD61@rica.net> <3DBA0A10.3445C604@rica.net>
Subject: Re: Bypass capacitor position
Date: Fri, 25 Oct 2002 22:57:56 -0500
X-Newsreader: Microsoft Outlook Express 6.00.2800.1106
X-Abuse-and-DMCA-Info: Please be sure to forward a copy of ALL headers
X-Abuse-and-DMCA-Info: Otherwise we will be unable to process your complaint properly
> I think there is not much difference ot the difference.
Point being, this chip's spiks current comes out of that cap, and that cap
only, the current loop is as small as possible.
> Do you carry this separation all the way back to the power regulator,
> or just on the circuit board?
In my systems, this is usually all on one board, but yes, if multi-board,
then a high current customer gets his own power and ground tracks, pins on
> I put a bit of high frequency impedance (ferrite bead on lead) between
> the positive supply and the local bypass capacitor for the stepper
> drive, and keep the ground gridded. This also forces the local bypass
> to carry almost all the high frequency currents, while keeping the
> ground as clean and consistent as possible for the circuits
> communicating with the drive circuits. I put the highest current
> loads closest to the supply connector, so that any drop it causes
> getting from supply ot board are common to all circuits.
I like the ferrite, but gridding the ground means that it will take the
shortest path / lowest Z path it can find, which may not be the best path.
> Won't know till we measure two otherwise similar designs. I would
> love to have time to have a design contest. :)
I've been experimenting over the years, trying one thing or another on each
set of boards.
Slow, but rewarding.