Nah, you still have a year, at least in the US. Folks have been selling those 14-in-one input protection gizmos forever--the first I knew of was the Harris SP720, back in about 1990. I still have some--they were pretty bullet-resistant.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal ElectroOptical Innovations 55 Orchard Rd Briarcliff Manor NY 10510 845-480-2058 hobbs at electrooptical dot net http://electrooptical.net
Yeah, but they didn't use the "float the rails" trick :-))
I am not much of a fan of the ESD protection gizmos. They often fall from grace with the marketeers and then become a purchasing nightmare. Then you have to find something pin-compatible and drive it through the ECO release process or at least get a deviation signed. According to Murphy this happens on a Friday and the flight that is supposed to take your family to the resort on East Rarotonga leaves in seven hours, all non-refundable tickets.
-- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
don't
leave
inputs
In the datasheets for HC405x cheapie analog mux I read recently ;)
Grant.
Simple but fairly accurate shunt regulator (TL431, maybe boost?) to dump excess current, at least it's shared for all inputs so can have more care, components.
Grant.
So _that_'s why you became a consultant. ;)
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal ElectroOptical Innovations 55 Orchard Rd Briarcliff Manor NY 10510 845-480-2058 hobbs at electrooptical dot net http://electrooptical.net
Actually no. We haven't taken a vacation in over a decade. But it's not so much job related, more because of all the volunteers stuff and the fact that we have three large dogs. But as a consultant you do a whole lot more crisis-type work than as an employee. That's because we often get called in at the last minute, when stuff has already hit the fan, big time.
-- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
so
aW is
But you have to provide two new power rails? This isn't a passive solution. At some point you are just better off buying the protection diodes, probably from both a cost and reliability standpoint.
What's hard about this? I've been doing this for years, I hope it's not novel?
Tim
-- Deep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms
Piece of cake. A BAV99, a resistor and a 10uF ceramic of the super-bargain class foer each rail, that's pretty much it. Around 10 cents worth of parts.
Any suggestions how to do it for less money?
-- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
Actually, semi-auto p+p puts strain on bodies, so we try to design with the minimum number of parts. That means more resistor/diode packs, dual and quad opamps, wide-bus logic chips, things like that.
Our in-house placement costs are high, too. Analog design uses a lot of different part values, and many boutique parts, so it's hard to get everything on reels.
I can run DG408-type mux chips at +12. One recent board, I ran them at
+-17, by bootstrapping 5-volt DC-DC converters on top of my +-12 rails. A whole nother story.What I really need is a low-leakage high/low clamp device with many in one package. Providing overall clamp rails is easy; it's the 128 hi/lo clamps I'd like a clever solution for.
John
Can't be novel, I thought up similar scheme last month, used a TL431 'cos I didn't have a 3V9 zener handy ;) Run a small current thru the zener to define the voltage, and a low leakage diode to the signal. Didn't put the cap in 'cos the RC in signal line where I clamp has one.
Remember your cap for next time.
The luxury of clamp planes? John would go for that ;) Could put fast power amp/sinker like they do for mid-rail active termination of signals, like the older SCSI signals? Diode coupled instead of R coupled.
Grant.
Used to be +/- 10V signals on +/- 15V rails was plenty for everyone ;)
Yeah, tossing ideas about 'til someone hits the bullseye!
Did you measure ESR diodes to see of they leak low enough?
Spec (Philips) says 5 or 10uA over temperature for HCMOS tristate outputs, 20mA I/O diode, 70mA for bus driver Vcc, Gnd. Seems too much?
8 bit addr comparator gives you 17 inputs for 20 pin pkg? Back to 50mA for supply commons. HC688?Grant.
[...]
Same with cars. Nowadays everyone "needs" 150-200 horses to commute to work. Back when I was a kids dad pulled a 1.2-ton travel trailer with a
55HP car, family of five in the car, lots of luggage, food, a tent, plus an inflatable boat inside the trailer. [...]
Under normal temps around 70-80F it's usually well under 1uA.
[...]-- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
[snip]
On level ground, with a tail-wind ?:-)
I prefer 345hp myself... 25+MPG at a steady 80MPH :-)
As for MUX protection, how about simple-minded...
Diodes, transistors, resistors, capacitors: users-choice. ...Jim Thompson
--
| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
Spice is like a sports car...
Performance only as good as the person behind the wheel.
The right one looks quite busy WRT to SMT placement costs. The left one is nice but you might want to up the cap to 10uF or so in case the mother of all spikes comes waltzing in.
-- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
Which is why I asked about using arrays early on.
I don't believe spikes were the issue... simple over-range protection for a MUX. ...Jim Thompson
--
| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
Spice is like a sports car...
Performance only as good as the person behind the wheel.
What's hard is that I'd need 256 low-leakage diodes. That's a lot of parts.
The clamp rails are easy. One way to make them is to use regular
3-terminal voltage regulators "upside down", dumping current into ground. There are lots of ways to make the sink rails; I'd only need two for the entire board.John
Remember to use diodes in non-transparent packages.
A protection diode in a transparent package will make a nice light meter :-).
I'm going to state the problem a little more generally. Signal processing power per square inch of PCB space is simply ginormous these days. A chip the size of a fingernail can (like John's analog mux) marshall a hundred analog inputs.
The issue is, (correct me if I'm wrong John), is that the input signal conditioning to protect against even mild overloads often takes many more parts and (this is the kick in the teeth for me) PCB space.
In the multi-hundred to multi-thousand channel systems I deal with, we have been dealing with the problem at the cabling level. Signals come in (for example) on 60-conductor twist-and-flat differential pairs. We have a standard PCB that terminates the twist-and-flat, applies signal conditioning, and then comes into the marshalling stage. We just copied this from other companies in the 80's.
But even the above doesn't scale sufficiently. It was kind-of OK for the 80's but even the wiring systems have gotten much smaller since then. IMHO we should be moving the signal conditioning to the place where the analog voltages are being made, do the A/D there, and haul back everything over some high-speed optical or differential copper bus rather than do a "home run" of every analog voltage in the laboratory or car back to some common rack. I have succeeded in some cases with this but it'll take a broad systemic redesign, not some quick and dirty thing I can do at the data acquisition end.
Am I too far off John?
Well, my narow problem is to prevent customer over-voltage inputs from blowing through my analog multiplexers, and do that without putting a couple of hundred parts on my board. But the issue you bring up is real. Running fire-hose equivalent cables to a central location is expensive. We've been considering scattering i/o out in the field, as small boxes with one ethernet or maybe PoE cable running into the system. That has its problems too, like if the boxes would wind up in a temperature/altitude chamber near the DUT, sixty feet off the ground. But that little ethernet box still has ICs that need overload protection!
Most of our VME modules have a calibration connector and a relay per channel, so our customer can switch every channel to a traceable dvm/source and verify calibration before and after every test run, without disconnecting field wiring. That works well with all the gear in one rack, but would be very messy to attempt with distributed i/o.
John
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