Hi,
I would like to convert signal at 12volt to a 3.3v for connecting it to input pin of a spartan3 fpga. And then convert 3.3v output of spartan to 12 v , I'm not really use with designing board, I looked around but I did'nt achieve to find a lot of information. Should I use buffer with gain??
However does someone know where I could find information and teach about this kind of stuff like designing board...
thanks for your answer
regards
kcl
I think I have found what I need : a level shifter for TTL to CMOS should work fine
depends on how long you want the TTL gate to live :-)
He hasn't received a reply but he did find an answer to his question. I was wondering what other people could recommend.
Thanks, Derek
No, a typical TTL input is not designed to work with 12V input signals. Depending on what you are actually trying to achieve you might want to take a look at RS-232 transceivers.
/Mikhail
[for 12V FPGA level shifters]
For the input side of things, I would have thought that RS-232 receivers were a pretty good idea - they tolerate
+/-15V on their inputs, and can easily be got for 5V or 3.3V on the logic side. Don't forget they are usually inverting.On the output side, it depends what you're trying to drive. If you're OK with simply sinking current, most power MOSFETs these days will switch on hard with only 3V on their gates: source to ground, gate to logic, drain to 12V output is good - you can easily control an amp or more of current on the 12V side this way, with nothing more than a single FET per output. Zetex and Intersil have plenty of devices that will fit the bill. There's also the trusty old ULN2803 octal Darlington output drivers, and various similar devices. Think carefully, though, about where the return ground current (through the FET source) is likely to flow. You don't want it finding random paths around your logic PCB.
The big problem with all of this, in my experience, is that anyone trying to interface logic to 12V or 24V is probably playing around with industrial stuff. In that world, you can reliably assume that the electrical environment on the high-voltage side is totally crap. Sharing this filthy ground or power with your precious little 3.3V FPGA is asking for trouble. Inputs are quite likely to suffer significant voltage spikes, lots of nasty noise from horrible switches and motors and spark gaps and welding equipment and all that brutal stuff that you find around a typical industrial environment. Plant electricians have little patience with namby-pamby electronics and can be trusted to connect 110V AC to your sensing inputs, just for a giggle, to see how good your protection circuits really are. Logic designers are not welcome in a world where electrical connections are made with a quarter-inch wrench.
If you're in the automotive world for your 12V, then it's just as bad. Remember that load dump effects can cause +/- 60V transients on power and control wires. Take a look at CANbus transceiver chips from Philips and others (82C251 rings a bell, but someone better check - it's been a long time...) to see how bulletproof it's possible to make 'em.
Optical isolation *always* sounds like a good idea if you are in a dirty environment. Just don't expect it to be small or cheap :-(
Just in case anyone asks: no, this is not simply pen-and-paper cynicism. Been there, got it wrong, got the burn-marks to prove it.
-- Jonathan Bromley, Consultant DOULOS - Developing Design Know-how VHDL, Verilog, SystemC, Perl, Tcl/Tk, Verification, Project Services Doulos Ltd. Church Hatch, 22 Market Place, Ringwood, BH24 1AW, UK Tel: +44 (0)1425 471223 mail:jonathan.bromley@doulos.com Fax: +44 (0)1425 471573 Web: http://www.doulos.com The contents of this message may contain personal views which are not the views of Doulos Ltd., unless specifically stated.
Input signals (12 V driving into your 3.3V FPGA) are not the problem. Unless your signals are superfast (which they most likely are not) just insert a series resistor of, say, 10 kilohm. That, in conjunction with the internal clamping diode to Vcco, takes care of any high voltage up to tens of volts, and slows you down only by about 100 ns. Good idea for any input in the "industrial" world.
The output side requires some kind of high-voltage driver. And observe Jonathan's warnings!
Peter Alfke, Xilinx Applications
If you don't need very fast response (most 12 V logic is not high speed, anyway) then opto-couplers can be a good solution, as long as you can get a couple mA from the 12 V logic. I have a commercial product using 5 V Spartan FPGAs where I use the output of an H11A817D optocoupler to drive the Spartan input, using the Spartan's internal pull-up as the load resistor. This should work fine on 3.3 V FPGAs, too.
The same optocoupler can be used as an output, by having the FPGA output pull current through the opto's LED.
Jon
Hi Jonathan, So, thanks for a good post as ever! Just to pedantically whinge on about a pet subject of mine, I would recommend sharing the ground as tightly as you can. Provided you have a good multi-layer board with ground planes, you'll make things much easier than if you have a separate ground. Bits of metal floating around in electrically noisy environments can re-radiate in the most irritating and unpredictable way, acting like antennas. Even very large currents passing through your ground planes don't affect the circuit provided the board supplies are tightly coupled to the ground - in other words use lots of bypass caps. All this assumes you took the other eminently sensible precautions you describe, i.e. I/O protection and power supply filtering. Cheers, Syms. p.s. I learn something from every post. From this one I learnt that the plural of antenna is only antennae when they're on animals! The sad life of the pedant is never simple.
Sounds good to me, with the proviso...
Please, can someone explain what's sad about it? A pedant is someone who prefers their opinions to be correct.
-- Jonathan Bromley, Consultant
DOULOS - Developing Design Know-how VHDL, Verilog, SystemC, Perl, Tcl/Tk, Verification, Project Services
Doulos Ltd. Church Hatch, 22 Market Place, Ringwood, BH24 1AW, UK Tel: +44 (0)1425 471223 mail: snipped-for-privacy@doulos.com Fax: +44 (0)1425 471573 Web:
The contents of this message may contain personal views which are not the views of Doulos Ltd., unless specifically stated.
Indeed so, although that's one of the older ones - TJA1050 is a more current one - apply -27 to 40V to the CAN pins for as long as you like, +-200 V transients as well!
There's a great series of scope shots of real automotive transients from things like windscreen wipers in a paper I can't find at the moment - regular 70V spikes every time the intermittent wipers triggered IIRC! I'll try and dig them out...
Cheers, Martin
-- martin.j.thompson@trw.com TRW Conekt - Consultancy in Engineering, Knowledge and Technology http://www.trw.com/conekt
Through bitter (and occasionally painful) experience I've discovered that not everybody enjoys having their grammar, punctuation and spolling corrected at every possible opportunity. Especially your nearest and dearest. To paraphrase the (apparently falsely accredited) words of Churchill on the occasion of him being corrected for ending a sentence with a preposition (Good grief, what was he thinking of?), "It is the kind of arrant pedantry up with which they will not put." I refer you to this article:-
You entered that typo on purpose, didn't you?
Kolja
LOL! What a classic!
Regards, Mark
Best one I've seen recently was Litterature in an anti-spam group discussing the 2005 Ig Noble prizes:
LITERATURE: The Internet entrepreneurs of Nigeria, for creating and then using e-mail to distribute a bold series of short stories, thus introducing millions of readers to a cast of rich characters -- General Sani Abacha, Mrs. Mariam Sanni Abacha, Barrister Jon A Mbeki Esq., and others -- each of whom requires just a small amount of expense money so as to obtain access to the great wealth to which they are entitled and which they would like to share with the kind person who assists them.
-- The suespammers.org mail server is located in California. So are all my other mailboxes. Please do not send unsolicited bulk e-mail or unsolicited commercial e-mail to my suespammers.org address or any of my other addresses. These are my opinions, not necessarily my employer's. I hate spam.
Found them - in the proceedings of the Automotive EMC Conference 2003 "Transient Test Requirements for e-Marking - Necessity or Bureaucracy?" Unfortunately not available for free as far as I can tell :-(
One car generated -110V with 8ns rise time when the fan speed for the heater was changed! The intermittent wipers were only 25V, 80ns risetime - quite tame really.
Cheers, Martin
-- martin.j.thompson@trw.com TRW Conekt - Consultancy in Engineering, Knowledge and Technology http://www.trw.com/conekt
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