esd diodes as diodes
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From: Joerg on 4 Aug 2010 18:01 Phil Hobbs wrote: > On 8/4/2010 5:18 PM, Joerg wrote: >> Jim Thompson wrote: >>> On Wed, 04 Aug 2010 11:50:12 -0700, Joerg<invalid(a)invalid.invalid> >>> wrote: >>> >>>> Grant wrote: >>> [snip] >>>>> I'm sure the pick'n'placer wont complain too much ;) >>>>> >>>>> You can run the mux chip at 6V? Clamp to 5V at the front for mux, >>>>> look after the ADC separately on other side of mux? >>>>> >>>> Or when using a cheap CMOS chip of the 74HC type, run its GND a diode >>>> drop above GND and its VCC a diode drop below the mux supply. Bypass >>>> both independently and clamp those artificial rails somewhere so they >>>> can't be pumped up. That way the mux substrate diodes shall never see >>>> any significant currents going into them. >>>> >>> [snip] >>> >>> Interesting idea. I'll see if it's twistable into an active, lo-Z, >>> clamp >>> >> >> Hey, I wanted to patent that ... oh, too late ... >> > 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. > 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.
From: Phil Hobbs on 4 Aug 2010 20:03 Joerg wrote: > Phil Hobbs wrote: >> On 8/4/2010 5:18 PM, Joerg wrote: >>> Jim Thompson wrote: >>>> On Wed, 04 Aug 2010 11:50:12 -0700, Joerg<invalid(a)invalid.invalid> >>>> wrote: >>>> >>>>> Grant wrote: >>>> [snip] >>>>>> I'm sure the pick'n'placer wont complain too much ;) >>>>>> >>>>>> You can run the mux chip at 6V? Clamp to 5V at the front for mux, >>>>>> look after the ADC separately on other side of mux? >>>>>> >>>>> Or when using a cheap CMOS chip of the 74HC type, run its GND a diode >>>>> drop above GND and its VCC a diode drop below the mux supply. Bypass >>>>> both independently and clamp those artificial rails somewhere so they >>>>> can't be pumped up. That way the mux substrate diodes shall never see >>>>> any significant currents going into them. >>>>> >>>> [snip] >>>> >>>> Interesting idea. I'll see if it's twistable into an active, lo-Z, >>>> clamp >>>> >>> Hey, I wanted to patent that ... oh, too late ... >>> >> 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. >> > > 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. > 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
From: Joerg on 4 Aug 2010 20:33 Phil Hobbs wrote: > Joerg wrote: >> Phil Hobbs wrote: >>> On 8/4/2010 5:18 PM, Joerg wrote: >>>> Jim Thompson wrote: >>>>> On Wed, 04 Aug 2010 11:50:12 -0700, Joerg<invalid(a)invalid.invalid> >>>>> wrote: >>>>> >>>>>> Grant wrote: >>>>> [snip] >>>>>>> I'm sure the pick'n'placer wont complain too much ;) >>>>>>> >>>>>>> You can run the mux chip at 6V? Clamp to 5V at the front for mux, >>>>>>> look after the ADC separately on other side of mux? >>>>>>> >>>>>> Or when using a cheap CMOS chip of the 74HC type, run its GND a diode >>>>>> drop above GND and its VCC a diode drop below the mux supply. Bypass >>>>>> both independently and clamp those artificial rails somewhere so they >>>>>> can't be pumped up. That way the mux substrate diodes shall never see >>>>>> any significant currents going into them. >>>>>> >>>>> [snip] >>>>> >>>>> Interesting idea. I'll see if it's twistable into an active, lo-Z, >>>>> clamp >>>>> >>>> Hey, I wanted to patent that ... oh, too late ... >>>> >>> 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. >>> >> >> 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. >> > > So _that_'s why you became a consultant. ;) > 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.
From: Tim Williams on 5 Aug 2010 05:39 <miso(a)sushi.com> wrote in message news:37c28984-3697-42e3-b1e9-30edbfe39f3b(a)j8g2000yqd.googlegroups.com... > 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? http://myweb.msoe.edu/williamstm/Images/Input_Protection.png Clamp diodes unmarked, substitute as desired. http://myweb.msoe.edu/williamstm/Images/Input_Protection2.png Works the same for single-supply operation (note the input diodes seem to be drawn upside down), keeping in mind the sum zener voltages are greater than the supply. 3.9V diodes would work on a 5V supply. If more stability is required, they could be boosted with emitter followers. You only need one rail for all the inputs, and you don't need to spend any PCB space doing it, you could quite rightfully substitute ground planes with clamp planes along the input edge. Tim -- Deep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms
From: Grant on 5 Aug 2010 17:07
On Thu, 5 Aug 2010 04:39:59 -0500, "Tim Williams" <tmoranwms(a)charter.net> wrote: ><miso(a)sushi.com> wrote in message >news:37c28984-3697-42e3-b1e9-30edbfe39f3b(a)j8g2000yqd.googlegroups.com... >> 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? >http://myweb.msoe.edu/williamstm/Images/Input_Protection.png >Clamp diodes unmarked, substitute as desired. 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. > >http://myweb.msoe.edu/williamstm/Images/Input_Protection2.png >Works the same for single-supply operation (note the input diodes seem to >be drawn upside down), keeping in mind the sum zener voltages are greater >than the supply. 3.9V diodes would work on a 5V supply. If more stability >is required, they could be boosted with emitter followers. You only need >one rail for all the inputs, and you don't need to spend any PCB space >doing it, you could quite rightfully substitute ground planes with clamp >planes along the input edge. 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. > >Tim |