On Mon, 21 Oct 2013 07:12:31 -0700, John Larkin <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:>On Mon, 21 Oct 2013 00:07:50 -0700 (PDT), Anthony Stewart ><tony.sunnysky@gmail.com> wrote: > >>All CMOS chips use Schottky diodes to both +/- rails to prevent SCR latchup and provide ESD protection. A series current limiting resistor is adequate. > >No. The "5 volt tolerant" parts usually allow +7 on pins, regardless of VCC.And the ESD diodes don't prevent latchup, they are the cause of latchup. And the diodes aren't schottky. -- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom timing and laser controllers Photonics and fiberoptic TTL data links VME analog, thermocouple, LVDT, synchro, tachometer Multichannel arbitrary waveform generators
5-volt tolerant CMOS
Started by ●October 20, 2013
Reply by ●October 21, 20132013-10-21
Reply by ●October 21, 20132013-10-21
On Monday, October 21, 2013 11:27:10 AM UTC-4, John Larkin wrote:> On Mon, 21 Oct 2013 07:44:32 -0700 (PDT), bloggs.fredbloggs.fred@gmail.co=m>=20 > wrote: >=20 >=20 >=20 > >On Sunday, October 20, 2013 10:47:07 PM UTC-4, John Larkin wrote: >=20 > >> On Sun, 20 Oct 2013 18:43:58 -0700 (PDT), bloggs.fredbloggs.fred@gmail=.com>=20 > >>=20 >=20 > >> wrote: >=20 > >>=20 >=20 > >>=20 >=20 > >>=20 >=20 > >> >On Sunday, October 20, 2013 3:24:53 PM UTC-4, John Larkin wrote: >=20 > >>=20 >=20 > >> > >=20 > >>=20 >=20 > >> >>=20 >=20 > >>=20 >=20 > >> >> have to add a part, it could be a tiny schottky diode to +5. I just=begrudge>=20 > >>=20 >=20 > >> >>=20 >=20 > >>=20 >=20 > >> >> every part on this schematic; the PCB will be under 2 square inches=. I'll be>=20 > >>=20 >=20 > >> >>=20 >=20 > >>=20 >=20 > >> >> using a dual opamp and the other half needs to be powered from +12,=so the one>=20 > >>=20 >=20 > >> >>=20 >=20 > >>=20 >=20 > >> >> that I'm gain-switching x1/x10 with the mux is +12 too. >=20 > >>=20 >=20 > >> > >=20 > >>=20 >=20 > >> > >=20 > >>=20 >=20 > >> >What are you switching, the feedback resistor in a basic inverting co=nfiguration, or what is it?>=20 > >>=20 >=20 > >>=20 >=20 > >>=20 >=20 > >> Non-inverting, opamp and two resistors and the mux. >=20 > >>=20 >=20 > >>=20 >=20 > >>=20 >=20 > >>=20 >=20 > >>=20 >=20 > >> --=20 >=20 > >>=20 >=20 > >>=20 >=20 > >>=20 >=20 > >> John Larkin Highland Technology Inc >=20 > >>=20 >=20 > >> www.highlandtechnology.com jlarkin at highlandtechnology dot com ==20>=20 > >>=20 >=20 > >>=20 >=20 > >>=20 >=20 > >> Precision electronic instrumentation >=20 > >>=20 >=20 > >> Picosecond-resolution Digital Delay and Pulse generators >=20 > >>=20 >=20 > >> Custom timing and laser controllers >=20 > >>=20 >=20 > >> Photonics and fiberoptic TTL data links >=20 > >>=20 >=20 > >> VME analog, thermocouple, LVDT, synchro, tachometer >=20 > >>=20 >=20 > >> Multichannel arbitrary waveform generators >=20 > > >=20 > >Is it a current feedback amp or something, otherwise how could you possi=bly approach the current levels quoted to make the MUX act up?>=20 >=20 >=20 > AD8034 is rated for 60 mA short-circuit current, typ. I have an unused 1K=r-pack>=20 > section nearby, so I can limit the current into the mux. But the FSA3157 =spec is>=20 > fuzzy about what happens in the pullup direction. >=20 >=20 >=20 > As Lasse points out, the analog pins probably have ESD diodes to Vcc, but=the>=20 > datasheet footnote is ambiguous. >=20 >=20 >=20 > I was more generally interested in what the input circuit is like in thos=e "5>=20 > volt tolerant" parts and I was hoping somebody would know. >=20 >=20 >=20 > As Phil notes, most analog mux's behave badly if you do turn on the esd d=iodes,>=20 > and the manufacturers must hire the NSA to make sure none of their data s=heets>=20 > or appnotes reveal that fact. >=20 >=20 >=20 >=20 >=20 > --=20 >=20 >=20 >=20 > John Larkin Highland Technology Inc >=20 > www.highlandtechnology.com jlarkin at highlandtechnology dot com =20 >=20 >=20 >=20 > Precision electronic instrumentation >=20 > Picosecond-resolution Digital Delay and Pulse generators >=20 > Custom timing and laser controllers >=20 > Photonics and fiberoptic TTL data links >=20 > VME analog, thermocouple, LVDT, synchro, tachometer >=20 > Multichannel arbitrary waveform generatorsDidn't you say you have a non-inverting configuration with the MUX selectin= g X1/X10- that sounds like an R from OUT to IN(-) and then a resistor R/9 f= rom IN(-) to MUX common with the B0/B1 open/GND or something similar, (or i= s there too much leakage for that?)-seems like the currents into an over-vo= ltaged MUX can be made real small.
Reply by ●October 21, 20132013-10-21
On Sun, 20 Oct 2013 11:03:02 -0700, John Larkin <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:> > >Lots of CMOS gates and such are tolerant of pin voltages above Vcc, typically >rated for 7 volts max. Does anybody know what sort of input circuits are >typically used? Does it behave like a zener? To ground? > >Some parts specify an allowed input curent in the pullup direction, some don't. > >I'm designing a really tiny board, and an opamp can potentially overdrive an >analog mux, an FSA3157. I can current limit it with a "free" resistor, in a >pack, but a diode would take more room.It appears that particular one has diodes on the switch input clamping to Vcc/GND, but a zener-like structure on the control input for 5V tolerance, clamping to >+7 (presumably current flows to GND, not Vcc) and GND. As an aside, that's quite a bit of dissipation if you take their 50mA figure seriously, max dissipation would probably limit the steady-state current. The switch inputs clamping to Vcc is often inconvenient since it can cause Vcc to rise unless you add additional parts. A few of the higher end AD analog switches have zener structures on the analog inputs and disconnect for overvoltage exceeding Vdd + Vt (which could still cause problems in the following circuitry). Look for switches that are guaranteed "off" with power off for this kind of functionality.
Reply by ●October 21, 20132013-10-21
On Sunday, October 20, 2013 2:03:02 PM UTC-4, John Larkin wrote:> Lots of CMOS gates and such are tolerant of pin voltages above Vcc, typically > > rated for 7 volts max. Does anybody know what sort of input circuits are > > typically used? Does it behave like a zener? To ground? > > > > Some parts specify an allowed input curent in the pullup direction, some don't. > > > > I'm designing a really tiny board, and an opamp can potentially overdrive an > > analog mux, an FSA3157. I can current limit it with a "free" resistor, in a > > pack, but a diode would take more room. > > > > > > -- > > > > John Larkin Highland Technology Inc > > www.highlandtechnology.com jlarkin at highlandtechnology dot com > > > > Precision electronic instrumentation > > Picosecond-resolution Digital Delay and Pulse generators > > Custom timing and laser controllers > > Photonics and fiberoptic TTL data links > > VME analog, thermocouple, LVDT, synchro, tachometer > > Multichannel arbitrary waveform generatorsSay what you want about Maxim, but they do have this incredible beyond-the-rails analog switch technology: http://www.maximintegrated.com/datasheet/index.mvp/id/7503
Reply by ●October 21, 20132013-10-21
On Mon, 21 Oct 2013 11:33:03 -0700 (PDT), bloggs.fredbloggs.fred@gmail.com wrote:>On Sunday, October 20, 2013 2:03:02 PM UTC-4, John Larkin wrote: >> Lots of CMOS gates and such are tolerant of pin voltages above Vcc, typically >> >> rated for 7 volts max. Does anybody know what sort of input circuits are >> >> typically used? Does it behave like a zener? To ground? >> >> >> >> Some parts specify an allowed input curent in the pullup direction, some don't. >> >> >> >> I'm designing a really tiny board, and an opamp can potentially overdrive an >> >> analog mux, an FSA3157. I can current limit it with a "free" resistor, in a >> >> pack, but a diode would take more room. >> >> >> >> >> >> -- >> >> >> >> John Larkin Highland Technology Inc >> >> www.highlandtechnology.com jlarkin at highlandtechnology dot com >> >> >> >> Precision electronic instrumentation >> >> Picosecond-resolution Digital Delay and Pulse generators >> >> Custom timing and laser controllers >> >> Photonics and fiberoptic TTL data links >> >> VME analog, thermocouple, LVDT, synchro, tachometer >> >> Multichannel arbitrary waveform generators > >Say what you want about Maxim, but they do have this incredible beyond-the-rails analog switch technology: >http://www.maximintegrated.com/datasheet/index.mvp/id/7503Three internal 35MHz charge pumps. Their guaranteed max leakage is pretty high, but they'd be great for low-distortion switching of reasonably low impedance/low voltage circuits. Not so great for precision. Hey, maybe John can use one of these as a bias generator for a PD-- they should output +35 and -27 from a 3-5V source. If they can actually be purchased.
Reply by ●October 21, 20132013-10-21
On Mon, 21 Oct 2013 09:42:52 -0700 (PDT), bloggs.fredbloggs.fred@gmail.com wrote:>On Monday, October 21, 2013 11:27:10 AM UTC-4, John Larkin wrote: >> On Mon, 21 Oct 2013 07:44:32 -0700 (PDT), bloggs.fredbloggs.fred@gmail.com >> >> wrote: >> >> >> >> >On Sunday, October 20, 2013 10:47:07 PM UTC-4, John Larkin wrote: >> >> >> On Sun, 20 Oct 2013 18:43:58 -0700 (PDT), bloggs.fredbloggs.fred@gmail.com >> >> >> >> >> >> wrote: >> >> >> >> >> >> >> >> >> >> >> >> >On Sunday, October 20, 2013 3:24:53 PM UTC-4, John Larkin wrote: >> >> >> >> >> >> > >> >> >> >> >> >> >> >> >> >> >> >> >> >> have to add a part, it could be a tiny schottky diode to +5. I just begrudge >> >> >> >> >> >> >> >> >> >> >> >> >> >> every part on this schematic; the PCB will be under 2 square inches. I'll be >> >> >> >> >> >> >> >> >> >> >> >> >> >> using a dual opamp and the other half needs to be powered from +12, so the one >> >> >> >> >> >> >> >> >> >> >> >> >> >> that I'm gain-switching x1/x10 with the mux is +12 too. >> >> >> >> >> >> > >> >> >> >> >> >> > >> >> >> >> >> >> >What are you switching, the feedback resistor in a basic inverting configuration, or what is it? >> >> >> >> >> >> >> >> >> >> >> >> Non-inverting, opamp and two resistors and the mux. >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> -- >> >> >> >> >> >> >> >> >> >> >> >> John Larkin Highland Technology Inc >> >> >> >> >> >> www.highlandtechnology.com jlarkin at highlandtechnology dot com >> >> >> >> >> >> >> >> >> >> >> >> Precision electronic instrumentation >> >> >> >> >> >> Picosecond-resolution Digital Delay and Pulse generators >> >> >> >> >> >> Custom timing and laser controllers >> >> >> >> >> >> Photonics and fiberoptic TTL data links >> >> >> >> >> >> VME analog, thermocouple, LVDT, synchro, tachometer >> >> >> >> >> >> Multichannel arbitrary waveform generators >> >> > >> >> >Is it a current feedback amp or something, otherwise how could you possibly approach the current levels quoted to make the MUX act up? >> >> >> >> AD8034 is rated for 60 mA short-circuit current, typ. I have an unused 1K r-pack >> >> section nearby, so I can limit the current into the mux. But the FSA3157 spec is >> >> fuzzy about what happens in the pullup direction. >> >> >> >> As Lasse points out, the analog pins probably have ESD diodes to Vcc, but the >> >> datasheet footnote is ambiguous. >> >> >> >> I was more generally interested in what the input circuit is like in those "5 >> >> volt tolerant" parts and I was hoping somebody would know. >> >> >> >> As Phil notes, most analog mux's behave badly if you do turn on the esd diodes, >> >> and the manufacturers must hire the NSA to make sure none of their data sheets >> >> or appnotes reveal that fact. >> >> >> >> >> >> -- >> >> >> >> John Larkin Highland Technology Inc >> >> www.highlandtechnology.com jlarkin at highlandtechnology dot com >> >> >> >> Precision electronic instrumentation >> >> Picosecond-resolution Digital Delay and Pulse generators >> >> Custom timing and laser controllers >> >> Photonics and fiberoptic TTL data links >> >> VME analog, thermocouple, LVDT, synchro, tachometer >> >> Multichannel arbitrary waveform generators > >Didn't you say you have a non-inverting configuration with the MUX selecting X1/X10- that sounds like an R from OUT to IN(-) and then a resistor R/9 from IN(-) to MUX common with the B0/B1 open/GND or something similar, (or is there too much leakage for that?)-seems like the currents into an over-voltaged MUX can be made real small.https://dl.dropboxusercontent.com/u/53724080/Circuits/Amps/Amp_X1_X10.JPG I was planning to use circuit A, with R1 to limit the current into the mux. The opamp supplies are +-12. Circuit B, which I think you are suggesting, also limits the current into the mux, but the mux resistance starts to matter and there are bandwidth penalties. Since R1 is free, I may as well use A. -- John Larkin Highland Technology, Inc jlarkin at highlandtechnology dot com http://www.highlandtechnology.com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom laser drivers and controllers Photonics and fiberoptic TTL data links VME thermocouple, LVDT, synchro acquisition and simulation
Reply by ●October 21, 20132013-10-21
John Larkin wrote:> On Mon, 21 Oct 2013 09:42:52 -0700 (PDT), > bloggs.fredbloggs.fred@gmail.com wrote: > >> On Monday, October 21, 2013 11:27:10 AM UTC-4, John Larkin wrote: >>> On Mon, 21 Oct 2013 07:44:32 -0700 (PDT), bloggs.fredbloggs.fred@gmail.com >>> >>> wrote: >>> >>> >>> >>>> On Sunday, October 20, 2013 10:47:07 PM UTC-4, John Larkin wrote: >>>>> On Sun, 20 Oct 2013 18:43:58 -0700 (PDT), bloggs.fredbloggs.fred@gmail.com >>>>> wrote: >>>>>> On Sunday, October 20, 2013 3:24:53 PM UTC-4, John Larkin wrote: >>>>>>> have to add a part, it could be a tiny schottky diode to +5. I just begrudge >>>>>>> every part on this schematic; the PCB will be under 2 square inches. I'll be >>>>>>> using a dual opamp and the other half needs to be powered from +12, so the one >>>>>>> that I'm gain-switching x1/x10 with the mux is +12 too. >>>>>> What are you switching, the feedback resistor in a basic inverting configuration, or what is it? >>>>> Non-inverting, opamp and two resistors and the mux. >>>>> -- >>>>> John Larkin Highland Technology Inc >>>>> www.highlandtechnology.com jlarkin at highlandtechnology dot com >>>>> Precision electronic instrumentation >>>>> Picosecond-resolution Digital Delay and Pulse generators >>>>> Custom timing and laser controllers >>>>> Photonics and fiberoptic TTL data links >>>>> VME analog, thermocouple, LVDT, synchro, tachometer >>>>> Multichannel arbitrary waveform generators >>>> Is it a current feedback amp or something, otherwise how could you possibly approach the current levels quoted to make the MUX act up? >>> >>> >>> AD8034 is rated for 60 mA short-circuit current, typ. I have an unused 1K r-pack >>> >>> section nearby, so I can limit the current into the mux. But the FSA3157 spec is >>> >>> fuzzy about what happens in the pullup direction. >>> >>> >>> >>> As Lasse points out, the analog pins probably have ESD diodes to Vcc, but the >>> >>> datasheet footnote is ambiguous. >>> >>> >>> >>> I was more generally interested in what the input circuit is like in those "5 >>> >>> volt tolerant" parts and I was hoping somebody would know. >>> >>> >>> >>> As Phil notes, most analog mux's behave badly if you do turn on the esd diodes, >>> >>> and the manufacturers must hire the NSA to make sure none of their data sheets >>> >>> or appnotes reveal that fact. >>> >>> >>> >>> >>> >>> -- >>> >>> >>> >>> John Larkin Highland Technology Inc >>> >>> www.highlandtechnology.com jlarkin at highlandtechnology dot com >>> >>> >>> >>> Precision electronic instrumentation >>> >>> Picosecond-resolution Digital Delay and Pulse generators >>> >>> Custom timing and laser controllers >>> >>> Photonics and fiberoptic TTL data links >>> >>> VME analog, thermocouple, LVDT, synchro, tachometer >>> >>> Multichannel arbitrary waveform generators >> Didn't you say you have a non-inverting configuration with the MUX selecting X1/X10- that sounds like an R from OUT to IN(-) and then a resistor R/9 from IN(-) to MUX common with the B0/B1 open/GND or something similar, (or is there too much leakage for that?)-seems like the currents into an over-voltaged MUX can be made real small. > > > https://dl.dropboxusercontent.com/u/53724080/Circuits/Amps/Amp_X1_X10.JPG > > I was planning to use circuit A, with R1 to limit the current into the > mux. The opamp supplies are +-12. >Couple of things to watch out for: a. Make sure the IN+ signal never exceeds the mux supplies, at least not driven from a hard source. Some opamps activate clamp circuitry or diodes if IN+ and IN- drift apart. b. If the mux supply rail isn't otherwise loaded use a TL431 to shunt a little above. Else the current through R1 would raise that voltage until ... *PHUT* [...] -- Regards, Joerg http://www.analogconsultants.com/
Reply by ●October 21, 20132013-10-21
Spehro Pefhany wrote:> > If they can actually be purchased.:) -- Reply in group, but if emailing remove the last word.
Reply by ●October 22, 20132013-10-22
On Monday, October 21, 2013 3:34:13 PM UTC-4, Spehro Pefhany wrote:> On Mon, 21 Oct 2013 11:33:03 -0700 (PDT), >=20 > bloggs.fredbloggs.fred@gmail.com wrote: >=20 >=20 >=20 > >On Sunday, October 20, 2013 2:03:02 PM UTC-4, John Larkin wrote: >=20 > >> Lots of CMOS gates and such are tolerant of pin voltages above Vcc, ty=pically>=20 > >>=20 >=20 > >> rated for 7 volts max. Does anybody know what sort of input circuits a=re>=20 > >>=20 >=20 > >> typically used? Does it behave like a zener? To ground? >=20 > >>=20 >=20 > >>=20 >=20 > >>=20 >=20 > >> Some parts specify an allowed input curent in the pullup direction, so=me don't.>=20 > >>=20 >=20 > >>=20 >=20 > >>=20 >=20 > >> I'm designing a really tiny board, and an opamp can potentially overdr=ive an>=20 > >>=20 >=20 > >> analog mux, an FSA3157. I can current limit it with a "free" resistor,=in a>=20 > >>=20 >=20 > >> pack, but a diode would take more room. >=20 > >>=20 >=20 > >>=20 >=20 > >>=20 >=20 > >>=20 >=20 > >>=20 >=20 > >> --=20 >=20 > >>=20 >=20 > >>=20 >=20 > >>=20 >=20 > >> John Larkin Highland Technology Inc >=20 > >>=20 >=20 > >> www.highlandtechnology.com jlarkin at highlandtechnology dot com ==20>=20 > >>=20 >=20 > >>=20 >=20 > >>=20 >=20 > >> Precision electronic instrumentation >=20 > >>=20 >=20 > >> Picosecond-resolution Digital Delay and Pulse generators >=20 > >>=20 >=20 > >> Custom timing and laser controllers >=20 > >>=20 >=20 > >> Photonics and fiberoptic TTL data links >=20 > >>=20 >=20 > >> VME analog, thermocouple, LVDT, synchro, tachometer >=20 > >>=20 >=20 > >> Multichannel arbitrary waveform generators >=20 > > >=20 > >Say what you want about Maxim, but they do have this incredible beyond-t=he-rails analog switch technology:>=20 > >http://www.maximintegrated.com/datasheet/index.mvp/id/7503 >=20 >=20 >=20 > Three internal 35MHz charge pumps. Their guaranteed max leakage is >=20 > pretty high, but they'd be great for low-distortion switching of >=20 > reasonably low impedance/low voltage circuits. Not so great for >=20 > precision.=20 >=20 >=20 >=20 > Hey, maybe John can use one of these as a bias generator for a PD-- >=20 > they should output +35 and -27 from a 3-5V source. If they can >=20 > actually be purchased.The guaranteed leakage is 10x better than the FSA3157, and the isolation is= about 30dB better, but the charge injection and terminal capacitance are w= hoa way bad for anything but a low impedance application. Switching times a= re immaterial for this app. It has a thermal shutdown capability, seems lik= e a first for an analog switch. The charge pump noise is way down at -80dBm= but not fantastic for precision signal conditioning. Maybe this not the be= st part for the application.
Reply by ●October 22, 20132013-10-22
On Mon, 21 Oct 2013 15:34:13 -0400, Spehro Pefhany <speffSNIP@interlogDOTyou.knowwhat> wrote:>On Mon, 21 Oct 2013 11:33:03 -0700 (PDT), >bloggs.fredbloggs.fred@gmail.com wrote: > >>On Sunday, October 20, 2013 2:03:02 PM UTC-4, John Larkin wrote: >>> Lots of CMOS gates and such are tolerant of pin voltages above Vcc, typically >>> >>> rated for 7 volts max. Does anybody know what sort of input circuits are >>> >>> typically used? Does it behave like a zener? To ground? >>> >>> >>> >>> Some parts specify an allowed input curent in the pullup direction, some don't. >>> >>> >>> >>> I'm designing a really tiny board, and an opamp can potentially overdrive an >>> >>> analog mux, an FSA3157. I can current limit it with a "free" resistor, in a >>> >>> pack, but a diode would take more room. >>> >>> >>> >>> >>> >>> -- >>> >>> >>> >>> John Larkin Highland Technology Inc >>> >>> www.highlandtechnology.com jlarkin at highlandtechnology dot com >>> >>> >>> >>> Precision electronic instrumentation >>> >>> Picosecond-resolution Digital Delay and Pulse generators >>> >>> Custom timing and laser controllers >>> >>> Photonics and fiberoptic TTL data links >>> >>> VME analog, thermocouple, LVDT, synchro, tachometer >>> >>> Multichannel arbitrary waveform generators >> >>Say what you want about Maxim, but they do have this incredible beyond-the-rails analog switch technology: >>http://www.maximintegrated.com/datasheet/index.mvp/id/7503 > >Three internal 35MHz charge pumps. Their guaranteed max leakage is >pretty high, but they'd be great for low-distortion switching of >reasonably low impedance/low voltage circuits. Not so great for >precision. > >Hey, maybe John can use one of these as a bias generator for a PD-- >they should output +35 and -27 from a 3-5V source. If they can >actually be purchased.Some sort of IC bias generator would be cute, if it didn't violate the Never Buy Maxim rule. As an analog switch, that has way too much personality. I'd just as soon use an opto-SSR. In my current project, I'll keep the pd bias supply out of the optical head. If I did put it on the same board with the photodiode, it would be a PV isolator or a soft, slow, low KHz charge pump. -- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom timing and laser controllers Photonics and fiberoptic TTL data links VME analog, thermocouple, LVDT, synchro, tachometer Multichannel arbitrary waveform generators
