Post by thread:[EE]: 4066 wired to external circuit

Would an analog switch IC that is passing signals from another board need to have its switch contact pins protected similar to the recommendation for microcontroller inputs? If so, how would one go about doing that without inhibiting the signal through the IC switch? In my case it's not a big deal to obstruct the signal, I'm not passing an analog signal that is attenuation sensitive, I'm just shorting two digital lines from afar and then releasing them after momentarily asserting them with the PIC. But if I should be ESD conscious again on this section of the circuit, I'd like to be prepared... -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

At 09:26 AM 10/11/2000 -0400, you wrote: >Would an analog switch IC that is passing signals from another board need to >have its switch contact pins protected similar to the recommendation for >microcontroller inputs? If so, how would one go about doing that without >inhibiting the signal through the IC switch? > >In my case it's not a big deal to obstruct the signal, I'm not passing an >analog signal that is attenuation sensitive, I'm just shorting two digital >lines from afar and then releasing them after momentarily asserting them >with the PIC. But if I should be ESD conscious again on this section of the >circuit, I'd like to be prepared... > 4066s are CMOS and thus subject to ESD. One possibility is adding transzorbs with a small series R at the input and output pins of the board. Ideally, these would be located right at the board edge, and it would be best to have the anodes of the transzorbs tied to a separate heavy gnd trace on the edge of the board so ESD currents would not be conducted thru the normal ckt gnd traces. This would not work with bipolar signals however. I/O <---R---+----> to 4066 | \---\ / \ --- | ------+--------separate gnd trace - danM -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

That's not an easy decision to make. However the consequences of leaving it vulnerable are less severe as it is an off-the-shelf part whereas a programmed micro at best takes time to replace. Also the scope for erratic operation is less. Also you have the option of looking at more robust analog switches. {Original Message removed}

From: "Dan Michaels" <spam_OUToricomTakeThisOuTUSWEST.NET> > 4066s are CMOS and thus subject to ESD. One possibility is adding > transzorbs with a small series R at the input and output pins of > the board Are those Transient Voltage Suppressors? I tried looking in the Digikey catalog for such devices and that's what I came across, never heard of them until today. If so, what kind of rating would I be looking at for this type of protective application? I feel like I suddenly don't know anything anymore, is this what everyone else felt like on their first day of college when they'd be asking what the point of a series circuit is and I'd be shaking my head in disbelief? -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

From: "Oliver Broad" <.....obroadKILLspam@spam@TELINCO.CO.UK> > However the consequences of leaving it vulnerable are less severe as it is > an off-the-shelf part I'm definitely socketing everything just to make it easy to fix any poor design decisions I make! > Also you have the option of looking at more robust analog switches. Any suggested device lines I could look into? I know there's other analog switches/multiplexors in the 4000 series like the 4053 triple 2 way I think, but other than the 4000 series I don't know of anything off hand. Maybe there's a TTL equivalent? -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

There's a number of devices prefixed DG, eg DG211 quad analog switch, similar to a 4066 but with much more versatile supply rails. 4000 series tends to be lowest cost though and often wins for that reason alone. The maxim website is worth a look, maxim-ic.com. Some of their ICs have specified levels of ESD resistance. Oliver. {Original Message removed}

Lorick wrote: >From: "Dan Michaels" <oricomKILLspamUSWEST.NET> > >> 4066s are CMOS and thus subject to ESD. One possibility is adding >> transzorbs with a small series R at the input and output pins of >> the board > >Are those Transient Voltage Suppressors? I tried looking in the Digikey >catalog for such devices and that's what I came across, never heard of them >until today. >If so, what kind of rating would I be looking at for this type of protective >application? > Yes, TVS devices. There are various types, but look at the SA5.0/etc series on page 277 of latest Digikey cat. These things are basically very low inductance fast acting breakdown diodes. I do believe the SAxx series were designed specifically for datacomm apps, and can handle decent signal rates, but you should verify this yourself. I recall that, if you put a regular zener on a data line to act as a clamp, it has such a high capacitance that it kills fast signals. So, there are two issues - one, speed of breakdown in response to noise spikes, and two, size of junction capacitance vis-a-vis how much the diode acts like a lo-Z for normal high frequency signals. Need to look at both, respecting your particular app. ================== >I feel like I suddenly don't know anything anymore, Ha - this only means you've been out of school for at least 6 months, say what. best regards, - Dan Michaels Oricom Technologies http://www.users.uswest.net/~oricom =================================== -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

Lorick wrote: >From: "Oliver Broad" <.....obroadKILLspam.....TELINCO.CO.UK> > >> However the consequences of leaving it vulnerable are less severe as it is >> an off-the-shelf part > >I'm definitely socketing everything just to make it easy to fix any poor >design decisions I make! > >> Also you have the option of looking at more robust analog switches. > >Any suggested device lines I could look into? I know there's other analog >switches/multiplexors in the 4000 series like the 4053 triple 2 way I think, >but other than the 4000 series I don't know of anything off hand. Maybe >there's a TTL equivalent? > Another possibility is to buffer the 4066 from the outside world using some kind of more robust chip - 'LS245, JFET opamp, etc - depends upon the exact signals being transferred. -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

Oliver Broad wrote: > > There's a number of devices prefixed DG, eg DG211 quad analog switch, > similar to a 4066 but with much more versatile supply rails. 4000 series > tends to be lowest cost though and often wins for that reason alone. > > The maxim website is worth a look, maxim-ic.com. Some of their ICs have > specified levels of ESD resistance. > > Oliver. Hi, they use 4066 in many TVs as the main switch for the AV inputs on the back of the set. This is quite common, and they don't fail very often. I think the 4066 is a lot more rugged than a standard cmos logic chip as its inputs are analogue and obviously different. The tv AV connectors get a lot of abuse, kids plugging games and everything in all the time. The standard protection the tv designers seem to use is a series resistor, a small ceramic cap of 220pF or so, and maybe a pull down resistor of a higher value. Sometimes the cap is in the middle of two series resistors if that makes sense, like a ladder network. Thye have been using this system in TVs for many years and I would do it without feeling too uncomfortable. Of course, if you wan't the *ultimate* in product reliability you might want to use the extra safety parts. I do this in our automotive applications. -Roman -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

Roman Black wrote: >Of course, if you wan't the *ultimate* in product reliability >you might want to use the extra safety parts. I do this in our >automotive applications. Hi Roman, Automotive environments are so incredibly noisy and spike prone. Could you give a brief rundown on the basic protection schemes used on the v.busses and I/O lines? best regards, - dan michaels -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

Dan Michaels wrote: > > Roman Black wrote: > > >Of course, if you wan't the *ultimate* in product reliability > >you might want to use the extra safety parts. I do this in our > >automotive applications. > > Hi Roman, > > Automotive environments are so incredibly noisy and spike prone. > Could you give a brief rundown on the basic protection schemes > used on the v.busses and I/O lines? > > best regards, > - dan michaels Hi Dan, now I'm not going to pretend to be some type of automotive electronics expert, as that is not my main field. But, I will say we have never had a product fail in service, and since many units we sell are used in racing motorcycles which often have no battery(!) and butchered charging systems I must be at least doing something right. I am a big believer in simplicity and overkill. Simplicity lets you use a big resistor as opposed to a smaller more expensive semiconductor or MOV spike suppressor etc. For the same parts cost you often get greater durability. Overkill to excess, I will use a 2w resistor in a circuit that dissipates 0.1w or even less. Resistors are cheap compared to the cost to you of a product that fails. My theory behind this comes from 20+ years of servicing TVs, etc, and it has been my experience that the most unreliable parts are any semiconductors, any varistors, any components full of corrosive (electro caps) and reliability is directly proportional to how cool any device runs. With the new tvs, I can touch the heatsinks for the the power semis and give you a pretty good estimate whether that semi will fail in 1 month, 1 year, 3 years, or never. Any service guy who fixes 50+ units a week will know what I am talking about. :o) For power filtering in auto applications I prefer simplicity of two large series resistors, with a cap to ground at the point between them. This is ideal for PIC apps which draw a small and regular current. I only use metal film resistors of course. Carbon resistors are a monstrosity! I use 630v polyester cap between the two series resistors (to gnd), these caps have better reliability than just about anything in that size and price range. With a 5v chip running from 12v auto, I drop about 4v across the resistors at normal running current and the other couple of volts with a low voltage drop out 3 pin regulator. I also use a 5w 24v zener to absorb transients that get through the two resistor ladder network. These big zeners last forever when spike buffered by a couple hundred ohms, mainly since it has zero temp as it doesn't conduct during normal operation. Yes I could use a 1w zener, but the 5w has a much larger silicon die and larger legs, and hence stronger mechanical coupling during heat expansion etc etc. Always us a BIG part if you want it to last forever, what the heck, costs 20c more per product! With a very low power app I would just use the two series resistors to a 5.1v zener, with a 630v poly cap and 24v zener at the spot between the two resistors, and obviously a large 22uf or more tantalum (did I mention I hate electros?) and this should suffice. When I was a kid I used to buy the ex-military and ex-commercial circuit boards from the local scrap dealer, and strip the parts for my hobby use. Surprise I found many of the electros were shot but NEVER found a dead tantalum. Also noticed the military stuff always used tantalums. How much price difference? How much do you want a little can of corrosive sandwiched between your heasinks? Yes I will sometimes use electros but only if no other choice, and I will use 105 degreeC types which have better rubber plugs and different corrosive type. Then I just prey that I mounted them far enough from any possible heat source. :o) With input/output buffering, again use the largest ohms value series resistor you can use, always use a buffer transistor, something like a little BC337 (800mA 50v) is tiny and cheap, but has a HUGE silicon die when compared to the in/out pins on a pic chip! If you buffer this with a decent series resistor and cap, it will be pretty bulletproof. If you need to run any decent output current from the PIC use a transistor with about 10x the current/pwr needed, again to use the maximum size silicon die and metal backing plate (never use a transistor you haven't pulled apart) etc. I like BD139/BD140, these have a huge backing plate and chunky die and are dirt cheap if you can fit the physical size. :o) Remember that MOV varistors and the like sound nice, but many types use an unstable metal "dust" compressed into a solid, and I have replaced so many of these things over the last few years I reject that as a solution. Nothing kills spikes as reliably as a RC network, or a RZ network and with good choice of R and C (or Z) it will do so forever. Many of the MOV type solutions are a trade off of "MOV kills spikes, which at the same time slowly kill MOV" that suits many TV/telecom manufacturers, but not suitable for a product I'm putting my name on! I apologise to the many professional engineers here for my "bucket science" solutions! I am not an engineer, I'm maybe a "re-engineer"?? ;o) -Roman -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! use EraseMElistservspam_OUTTakeThisOuTmitvma.mit.edu?body=SET%20PICList%20DIGEST

>Would an analog switch IC that is passing signals from another board >need to have its switch contact pins protected similar to the >recommendation for microcontroller inputs? If so, how would one go >about doing that without inhibiting the signal through the IC switch? Hi, the first point where to start with protection circuits for analog signals is the signal bandwidth. From that you can calculate easy the filter cut-off frequency on input. Filters could be realized from simple R and parasitic capacitance of tranzsorbs. If the capacitance of TZB is to high, then combination of fast schottky-diodes could be fine. If you need more protection, then you must use on input IC with ESD protection on input. Maxim or Linear do such IC, but costs little bit more. Regards, Andrej _________________________________________________________________________ Get Your Private, Free E-mail from MSN Hotmail at http://www.hotmail.com. Share information about yourself, create your own public profile at http://profiles.msn.com. -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! use listservspam_OUTmitvma.mit.edu?body=SET%20PICList%20DIGEST

>With a very low power app I would just use the two series resistors >to a 5.1v zener, with a 630v poly cap and 24v zener at the spot >between the two resistors, and obviously a large 22uf or more tantalum This sort of circuit has the added "hidden" protection against short circuits. remember that a Zener diode is normally connected in a manner that causes a "reverse voltage breakdown" (actually zener action) in normal use. When connected reverse polarity it will get only 0.6V across it, current limited by the first resistor, and the rest of the circuit is protected by the second resistor. Again using the largest zener you can fit will give it current capability that means it should survive any abuse. -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! use @spam@listservKILLspammitvma.mit.edu?bodyT%20PICList%20DIGEST

Andrej wrote: ......... >the first point where to start with protection circuits for analog signals >is the signal bandwidth. From that you can calculate easy the >filter cut-off frequency on input. Filters could be realized from simple R >and parasitic capacitance of tranzsorbs. If the capacitance of TZB is to >high, then combination of fast schottky-diodes could be fine. If you need >more protection, then you must use on input IC with ESD protection on input. >Maxim or Linear do such IC, but costs little bit more. > I looked at this a little further since mentioning the transzorbs yesterday. The lower voltage devices, which you would want to use to help protect chips, have a substantial parasitic capacitance - about 800 pF [much lower for higher V types]. Therefore they are not going to be very useful for "high" datarates, except possibly as part of a low-pass filter designed especially for the app. Xc = 1/[2*pi*F*C] = 1[2*pi*100Khz*800pF] = 1900 ohms @ 100Khz - danM -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! use KILLspamlistservKILLspammitvma.mit.edu?body=SET%20PICList%20DIGEST

{Quote hidden}>Andrej wrote: >......... > >the first point where to start with protection circuits for analog >signals > >is the signal bandwidth. From that you can calculate easy the > >filter cut-off frequency on input. Filters could be realized from simple >R > >and parasitic capacitance of tranzsorbs. If the capacitance of TZB is to > >high, then combination of fast schottky-diodes could be fine. If you need > >more protection, then you must use on input IC with ESD protection on >input. > >Maxim or Linear do such IC, but costs little bit more. > > > > >I looked at this a little further since mentioning the transzorbs >yesterday. The lower voltage devices, which you would want to use >to help protect chips, have a substantial parasitic capacitance >- about 800 pF [much lower for higher V types]. Therefore they >are not going to be very useful for "high" datarates, except >possibly as part of a low-pass filter designed especially for >the app. > >Xc = 1/[2*pi*F*C] = 1[2*pi*100Khz*800pF] = 1900 ohms @ 100Khz > >- danM > Dan, when you need protect High-Speed lines like satelite comunication, there are other tricks to do that. I just wanted to give a point, where to start the design. And it's allways signal bandwidth. When transzorbs are not useable, then other circuits may do the same job. What do you think? Andrej p.s.: By the way, EMC is sometimes nice game with ghosts and old bad witchs, mostly bewitching everything they can. Knowing some kinds of conjuring tricks, sometimes it's whisky, really very helpfull, you kill them. _________________________________________________________________________ Get Your Private, Free E-mail from MSN Hotmail at http://www.hotmail.com. Share information about yourself, create your own public profile at http://profiles.msn.com. -- http://www.piclist.com hint: To leave the PICList RemoveMEpiclist-unsubscribe-requestTakeThisOuTmitvma.mit.edu

Andy Jancura wrote: .......... >> >>I looked at this a little further since mentioning the transzorbs >>yesterday. The lower voltage devices, which you would want to use >>to help protect chips, have a substantial parasitic capacitance >>- about 800 pF [much lower for higher V types]. Therefore they >>are not going to be very useful for "high" datarates, except >>possibly as part of a low-pass filter designed especially for >>the app. >> >>Xc = 1/[2*pi*F*C] = 1[2*pi*100Khz*800pF] = 1900 ohms @ 100Khz >> > >Dan, when you need protect High-Speed lines like satelite comunication, >there are other tricks to do that. I just wanted to give a point, where to >start the design. And it's allways signal bandwidth. When transzorbs are not >useable, then other circuits may do the same job. What do you think? > Yes, of course, there are many different approaches to this problem, transzorbs being only one. Several years ago, I consulted with a company that used embedded controllers in industrial refrigeration units. This environment has horrendous ESD problems. We tried many ways to toughen the units, but through a process or trial and error found that transzorbs were the best defense, among several others, on the units. This did not really involve "high-speed" datacomm, and my calc from last time shows you probably have to go to something other than transzorbs in such a case. However, for a very low line impedance, you could still get reasonable performance when using TVS: Fbw = 1/[2*pi*R*C] = 1/{2*pi*50*800pf] = 3.9 Mhz best regards, - Dan Michaels Oricom Technologies http://www.users.uswest.net/~oricom =================================== -- http://www.piclist.com hint: To leave the PICList spamBeGonepiclist-unsubscribe-requestspamBeGonemitvma.mit.edu