It does, sorta. This is the simplest version. This application is only unidirectional (one in, twelve out). The others either require it to supply or accept power sorta like POE. We're looking for a discrete solution for that box but it'll be far too complicated, and large, for this box.
won't,
I don't know what your market is but there's a standard for pretty much everything. Medical, industrial, residential, aircraft, spacecraft, extraterrestrial restaurants, UFOs ...
No, that is standards committee bureaucrat speak for voltage difference. Reversing polarity would be ok, too.
If you find that your barrier needs to be wider than an 1812 or
20-something cap can bridge I'd use leaded parts. Larger ceramic caps can suffer stress fractures over time.-- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
I'm skeptical of the fence thing. Looking at the ege of a pc board, any dipole made from copper layers is tiny compared to the 1-meter wavelength at 300 MHz.
They seem to be comparing a 2-layer board to a multilayer. Not fair.
I'd guess that the major emitter is antennas caused by traces, not board-edge emission. What I'd do is make sure the power to the isolators is well bypassed close to the chips. The dipole effect, their fig 3, is probably serious. The stitching caps should help, if you can tolerate the side effects.
Ferrite beads in the signal leads that leave the board can work very well. If you're worried about EMI, I'd do that.
We have one board with 12 of the ADUM things and 12 DC/DC converters... 12 isolated 4-20 mA channels. The DC/DC sips caused a lot more trouble at 60 KHz than the isolators at 300 MHz.
This is all fuzzy stuff. Lots of opinions.
John
won't,
^^^^^^^^^^^^^^^^^^^^^^^^^^^^ How did you know? ;-)
I have never seen a real "standard" for anything.
Gotcha. Clarity in standards-speak has never been a priority (e.g. "grounded conductor" and "grounding conductor").
Leaded parts would seriously piss off the powers-that-be.
I was skeptical, too, but the polarity of the emissions suggest that's where it comes from. I should have (just) enough space to do it, so I'll try.
They also compared a more "standard" stackup to a tightly coupled G-V pair.
Side effects of the intrusion into the no-man's-land?
Yes, I've already put some 2.5K ferrites in the signal (and ground lines). There are a couple of other lines that already have 1K and 10K resistors in them, so I figured a ferrite was wasted. I also have a 390pF cap on the outbound side of the ferrite. That's something like .1ohm at 360MHz.
The problem is that these ADuM things have a power regulator built in. One, though I've decided not to use it for other reasons, can supply 100mA. It draws 290mA (34% efficiency) and has switching currents of .5A @ 180MHz!
Exactly. The boss has already acknowledged an extra spin in the board, though not because of anticipated EMI difficulty. Any port in a storm, though. ;-)
Yikes. We have done several boards where we made our own isolated supplies, using cheap ISDN-type transformers, driven with 60 KHz square waves with softened edges. That's pretty quiet, and certainly more efficient than 34%.
I wonder how much of that 66% loss is heat, and how much is radiated RF!
John
EMI
make
won't,
Actually the ones for aerospace are pretty good. Very down to earth, easy to understand. Meaning they were obviously written by real engineers.
Believe me, there is a standard for just about anything that has civilian, military, medical or commercial use.
[...]
Field failures down the raod probably even more so. Although a micro-fractured cap across the barrier probably won't be noticed. For a while ...
-- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
Do you have a favorite cheap XFMR type there that has 2nd source? In the past I've used European ones at times. ISDN never caught on too much in the US. The XFMRs are cheap alright but I've had purchasers complaining that the mfgs can sometimes be "difficult to deal with".
Probably mostly switching losses. Even if you got the transitions down to under 2nsec that's not very good at 180MHz.
-- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
They are sometimes long-lead. I think ISDN was a mediocre idea, lacking insight as to data rates to come.
The Talemas are 400 piece min, 16 weeks lately.
We buy custom ISDN-drop-in transformers from Minntronics. They wound us some with less inter-winding capacitance then the usual ones, and we can always get them.
Minntronics is great. Ask for Butch.
John
400 would be ok, 16wks not so much. Tamura is usually not in stock and Pulse wants a lot of money for theirs. Although, they do have 8-packs which you can get for around $4 in qties:
Thanks. Aren't they the folks who packed homebaked cookies with some shipments?
-- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
One,
Yeah, sometimes. They bake a batch of some sort of Swedish sugar cookies now and then.
John
EMI
make
won't,
I meant that I've never seen a standard for our market, well, other than the UL and CE stuff for the mains inputs. I looked up information on UL creepage numbers. It appears I can get away with 2mm (1206 caps).
That's the nice thing about standards; there are so many to choose from.
Likely never. They *do* know about TH parts, though. I'd think the lead inductance of a TH part would be much worse, too.
won't,
For this board I'm also in a big space crunch. I need to fit an isolated driver channel into about .6"x1".
Heat, mostly, I think. Chip-scale transformers aren't wonderful. I decided not to use the ADuM5201 because the ADM2587 turned out to be simpler. It supplies 15mA, which is more than enough with RS-422 transceiver swept under the covers.
[...]
There you go, that's exactly what I meant. CE/UL are the usual standards in the civilian world.
Usually not, the application or the target market point to a particular standard and then you don't really have a choice. If more than one market is to be served with your product it is possible that you have to adhere to more than one of the standards. But you can't wiggle out of a standard just to pick a more lenient one.
Doesn't have to be. After all, that's the way they made UHF TV-tuners in the 60's and those worked well above 300MHz ;-)
If you or the powers-that-be absolutely don't want to have through-hole there are L-bracketed long hi-rel SMT caps. But they'll cost ya. Even for a hi-rel client where cost isn't all that critical we opted for through-hole after looking at pricing. Because we'd have needed 50 of them (electrolytic avoidance).
-- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
This is the kind of thing that makes me wish books like AoE had a chapter on EM fields and waves. I asked Win Hill for it but no answer, so I guess the next edition will just have updated opamps. Not worth buying.
A coax is a waveguide, and non-conducting RF waveguides (no central conductor) are grounded at both ends. As far as the E field alone is concerned, I would guess it only needs to be held at ground potential from one end.
-- Reply in group, but if emailing add one more zero, and remove the last word.
I thought you meant standards for the market. There are none and few of our products go through UL or any like certification.
We don't do medical or aviation. There are no such standards.
The reality is that 300MHz is only the fundamental. We've had issues with the
100+ harmonic (not that I expect to even look at 30GHz).Price here likely isn't much of a problem. *I* would hate it, but management would likely not blink. They would *not* like TH parts. We already have too many of them (connectors).
Every market has standards. The UL/CE deals with safety, EMC and all that. That's what I meant, there are very few markets where you don't have to adhere to that. Alien spacecraft maybe, but only of those guys don't have trial lawyers ;-)
Then there's the other standards such as signal levels. Or the RS422 you just mentioned, because that's also a standard.
But you just mentioned UL/CE which is where you'll find (or already found) the answer to your creepage distance question. If your product can be handled by a living being, could cause a fire or any other harm, there will be a standard to adhere to. I have seen mfgs blissfully unaware of that but this does not relieve them of liability.
IME you almost have to migrate from board level to system level EMI mitigation once your concerns are spectra above half a gigeehoitz.
Ok, if the caps are not too large SMT may be ok. Make sure you get the proper ratings on the caps. If the barrier is a safety requirement that's one of the first thing the engineers at the notified body will likely want to see. Regular caps often do not have an AC rating so are typically a red flag to them. Y and X caps do have such ratings.
-- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
creepage
UL/CE, safety, yes, only where our customer demands it. EMC because governments demand it. The specific voltages or creepage requirements, nope, except on the mains side.
It's RS-422 because that's the standard we chose to use. It wasn't selected by someone else. We "own" both ends.
For the voltage protection *we* decide is useful. There is no standard for such.
On the mains side UL says something about this, sure. On the other end of the box, nope.
now,
IME, you have to start with the board to have any hope of system level compliance. In this particular box, there is little else other than the board and a steel box.
Any potential differences are in the grounds between boxes a couple of thousand feet away (which includes mobile units). Of course someone can mix the black and green wires, but I'd expect smoke somewhere.
the
creepage
Then you are ok, as long as your product specs don't claim a certain breakdown immunity.
[...]
now,
the
That is true, especially since you aren't bound by too much in safety requirements. A steel box offers nice system level shielding opportunities though.
Then I'd be careful. This sort of ground loop isolation function often falls under some standard. This is why many Ethernet transformers have breakdown voltage specs and often agency ratings.
-- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
Anyway, this means that *someone else* is dumping large amounts of current into ground, where he should have used a proper return conductor. It's definitely unneighbourly.
Jeroen Belleman
ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.