Re: Notches in ground planes for multi-power multi-channel board

On Sun, 10 Feb 2008 14:07:31 -0800 (PST), namdeguerre@xxxxxxxxx wrote:

All,

I am designing a multi-channel board and I have individual linear
regulators for each channel running off a common switcher.

Now, my concern is that due to the split power planes, which are like
thin fingers running through the board, I will cause potential
differences based on the current in different channels, especially,
because I have a common ground plane. Now, I was thinking my choices
are:

1) Split the ground plane as well, so I would have thin finger like
power and ground plane separated by narrow notch but connected at the
linear regulator end and at the input end. (All the channels are w.r.t
common ground plane.)

The trouble is, that I have common (to all channels) control lines
runnning across my planes (though separated by 2 layers) and even if I
isolate the grounds, some noise is bound to take the signal lines.

2) Keep split power planes, but add a narrow slice ground plane
between the power plane 'fingers' in between them on the same layer as
the power planes.

3) Keep 1, but put connections between ground planes at regular
intervals.

Anyone have thoughts on this. The voltages are +5 or less and it is
all analog..there are digital lines and a digital section, but they
come into the analog area through an isolator.

Keep one solid ground plane.

Using a linear regulator on each channel is a good way to isolate
power supply cross talk, so, keep that in.

You will have more problems with that switcher getting into things.
The switcher needs to be properly laid out on the pcb or you will get
switching noise into places you don't want it. Linear Tech. has the
layout of their reference designs for most or all of their switchers.
If you can't find it on LT's web site, call your LT rep. LT has
excellent customer support for the small guy. It is a good idea to use
LT's layout as a reference. If you can, use one of the MHz plus
switchers, then, apply ferrite beads to input and output of the
switcher.

---
Mark
.

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