Re: Routing sense lines of power supplies

On Fri, 12 Jun 2009 16:50:18 -0700, Joerg
<notthisjoergsch@xxxxxxxxxxxxxxxxxxxxx> wrote:

legg wrote:
On Fri, 12 Jun 2009 15:48:43 -0700, Joerg
<notthisjoergsch@xxxxxxxxxxxxxxxxxxxxx> wrote:

legg wrote:
On Fri, 12 Jun 2009 08:41:01 -0700 (PDT), a7yvm109gf5d1@xxxxxxxxxxx
wrote:

Just a CAD tool survey... Is there a tool that understands that there
can be a line on a power net that's actually meant to not connect to
any other part of the same net? (except on the pin of the sense line)
I use Allegro and I manually add no_shape_connect properties to vias
so that the sense line can route back to the supply without shorting
to the power plane. This seems silly.
Sense lines function on the basis of current flow through differing
micro-impedance tracing. This can be simplifiedfor CAD by introducing
an identifiable component, be it a low value resistor, link or other
physical object.

As practical remote sense lines may need an alternate remote
connection point, this isolating lower-impedance element is often
required anyways as a 'default' connection, in the event of an
open-circuit remote connection.

But that open circuit protector goes from sense to power trace, not in
series with the sense trace. So the sense trace is still the same node
as the power trace unless you put something in series as well, which
seems to be what the OP doesn't want to have to do anymore.

For simple single-fault abnormal ruggedness, any sense tracking should
have an identifiable impedance that can limit fault currents to some
level of survivability, if not repairability, for the duration of the
fault/protection interval. Simple tracking is unlikely to do this.

Open circuit board traces are not an acceptable result of a single
fault abnormal test in safety certification, regardless of their
location in the product. The cost is therefore easily justifiable in
any power circuit application requiring a safety certification.


Hmm, interesting, they never made us do that. But it does make sense in
situations where the proverbial wrench could fall into the unit. Or
wedding band etc. ... bzzzt ... *phoof*. Although that's not S.F.C. in
most gear because there is an enclosure.

Usually there is some sort of opamp input at the other end. When that
shorts out that part of the opamp just dies. The series resistor
wouldn't keep it from dying because that would be where the fault
started anyhow.

Fault duration and performance for survivability anticipates the
circuit single-fault behaviour, the fault protection processes that
are provided and the end result. All that the limiting impedance does
is to protect the board trace during this period - it does not
guarantee equipment operating integrity or single-fault performance:
that is for the designer to anticipate and to prove in the normal
process of product design and development.

Open board traces resulting from a single fault is a non-starter.

RL
.

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