LS,
Is there a thumbs rule connecting two layers.
On the bottom and on the top layer I have a GND polygon.
To reduce stray current I would like to connect these two using via's.
Regards
Harry
LS,
Is there a thumbs rule connecting two layers.
On the bottom and on the top layer I have a GND polygon.
To reduce stray current I would like to connect these two using via's.
Regards
Harry
In general, if they are to transmit high current, heat or digital
switching transients between the two ground conductors, you should place
alot of them. If the conductors are to be AC, or thermally, isolated,
only one. Not a simple topic, but most hobbyist circuits- doesn't really
matter.
Is there a package that one can calculate the voltage drop on a layer that
uses a polygon with or without via's?
"Gary Gofstein" <nospam@use.forum.net> schreef in bericht
news:hkvea1$h1m$1@cheetah.cadsoft.de...
In general, if they are to transmit high current, heat or digital
switching transients between the two ground conductors, you should place
alot of them. If the conductors are to be AC, or thermally, isolated, only
one. Not a simple topic, but most hobbyist circuits- doesn't really
matter.
No. You would need to know the distribution of the current for DC. For
AC currents in the RF range you need to know the shape of the pulse and
solve the wave equation to know where the current will flow and what
skin depth it will flow in. Nobody does that.
For "normal circuits", it's seldom an issue. How much current are we
talking about here anyway? DC, audio or RF current?
To get a comparison for DC currents you can look at trace temp rise vs
size charts for ordinary traces. You will see that unless you use super
thin "digital" traces, it's usually okay. I always use the biggest
traces I can fit anyway. There's a ULP that calculates temperature rise
on traces for DC currents; you'll see that your plane is likely to be
much bigger than necessary. You don't need to know how many vias to add,
because you should just add as many as you can to get the best
performance. You can estimate the temperature rise of a via by thinking
of it as a wire, figure out the equivalent wire guage, consult a
current vs temp rise site or chart to get the temp rise. You should
specify your vias to be solder filled for best DC and thermal
conductance. If you will never solder to them, you don't need thermals
on vias (EAGLE default anyway). Actually, it's possible to tack solder a
wire even on a via with no thermal, so it's rare to need a thermal on a
via. All this applies only to DC currents, RF/pulse currents are a whole
nother story...
Oh yeah, if you are thinking that knowing the voltage drop is important,
it may not be. If you plan on using that ground plane as a voltage
reference you should just run parallel ground traces that don't carry
current to anyplace that needs to know ground voltage (like an opamp
input or voltage regulator). These are separate from the plane returning
current to ground potential and generating voltage drops.
The plane should carry a current of approx. 3A at 18V DC
"Gary Gofstein" <nospam@use.forum.net> schreef in bericht
news:hl1u5s$8mk$1@cheetah.cadsoft.de...
No. You would need to know the distribution of the current for DC. For AC
currents in the RF range you need to know the shape of the pulse and solve
the wave equation to know where the current will flow and what skin depth
it will flow in. Nobody does that.
For "normal circuits", it's seldom an issue. How much current are we
talking about here anyway? DC, audio or RF current?
To get a comparison for DC currents you can look at trace temp rise vs
size charts for ordinary traces. You will see that unless you use super
thin "digital" traces, it's usually okay. I always use the biggest traces
I can fit anyway. There's a ULP that calculates temperature rise on traces
for DC currents; you'll see that your plane is likely to be much bigger
than necessary. You don't need to know how many vias to add, because you
should just add as many as you can to get the best performance. You can
estimate the temperature rise of a via by thinking of it as a wire,
figure out the equivalent wire guage, consult a current vs temp rise site
or chart to get the temp rise. You should specify your vias to be solder
filled for best DC and thermal conductance. If you will never solder to
them, you don't need thermals on vias (EAGLE default anyway). Actually,
it's possible to tack solder a wire even on a via with no thermal, so it's
rare to need a thermal on a via. All this applies only to DC currents,
RF/pulse currents are a whole nother story...