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
5-volt tolerant CMOS
Started by ●October 20, 2013
Reply by ●October 20, 20132013-10-20
Reply by ●October 21, 20132013-10-21
All CMOS chips use Schottky diodes to both +/- rails to prevent SCR latchup and provide ESD protection. A series current limiting resistor is adequate.
Reply by ●October 21, 20132013-10-21
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.--- According to TI and NXP, the diodes are polysilicon. Where does your Schottky information stem from? -- JF
Reply by ●October 21, 20132013-10-21
On Mon, 21 Oct 2013 03:48:27 -0500, John Fields <jfields@austininstruments.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. > >--- >According to TI and NXP, the diodes are polysilicon. > >Where does your Schottky information stem from?From his imagination. I know of NO situations where Schottky's are used for ESD. ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
Reply by ●October 21, 20132013-10-21
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. -- 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
Reply by ●October 21, 20132013-10-21
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 generatorsIs it a current feedback amp or something, otherwise how could you possibly approach the current levels quoted to make the MUX act up?
Reply by ●October 21, 20132013-10-21
John Larkin 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. >Careful with the signal path on mux chips. That "regardless of VCC" often only applies to the control inputs. -- Regards, Joerg http://www.analogconsultants.com/
Reply by ●October 21, 20132013-10-21
On 10/21/2013 3:07 AM, Anthony Stewart 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. >Even the CD4049UB? Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 USA +1 845 480 2058 hobbs at electrooptical dot net http://electrooptical.net
Reply by ●October 21, 20132013-10-21
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
Reply by ●October 21, 20132013-10-21
On Mon, 21 Oct 2013 07:45:04 -0700, Joerg <invalid@invalid.invalid> wrote:>John Larkin 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. >> > >Careful with the signal path on mux chips. That "regardless of VCC" >often only applies to the control inputs.I know... I was bitten by that in my youth. In most CMOS mux's, if the analog switch pin voltage goes beyond either rail, a supposedly "off" switch turns on in common-source mode. And sometimes ESD diode current gets sprayed all over the chip. -- 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
