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.

Best just to reference and decouple the output regulators to the load
at the ground plane of the load. input decoupling will only work with
an intervening impedance at the unregulated input.

If the switcher outputs had individual returns (ie were isolated) you
might do some funny stuff with the grounds before the regulators, but
not with a common return. You might consider runnung the switcher
return to an intelligent board location, before it hits the ground
plane.

RL
.

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