Reply by piglet April 18, 20202020-04-18
On 17/04/2020 12:12 pm, Pimpom wrote:
> I'm designing an analog circuit with a regulated +/-12V supply. I want > to include a 4000 series CMOS logic device to switch a sub-circuit at > sub-Hz frequency. > > I haven't worked out all the details but, at this stage, using ground as > Vdd and -12V as Vss looks like a convenient way to go. Is there any > reason why this is inadvisable? Any caveats? (Proper care will be taken > to ensure that no pin will be pulled outside Vdd and Vss).
The idea of "Ground" is a ghastly human simplification that mostly serves just to make schematics not look messy but hides the real truth! piglet
Reply by Pimpom April 17, 20202020-04-17
On 4/17/2020 8:26 PM, jlarkin@highlandsniptechnology.com wrote:
> On Fri, 17 Apr 2020 16:42:17 +0530, Pimpom <nobody@nowhere.com> wrote: > >> I'm designing an analog circuit with a regulated +/-12V supply. I >> want to include a 4000 series CMOS logic device to switch a >> sub-circuit at sub-Hz frequency. >> >> I haven't worked out all the details but, at this stage, using >> ground as Vdd and -12V as Vss looks like a convenient way to go. >> Is there any reason why this is inadvisable? Any caveats? (Proper >> care will be taken to ensure that no pin will be pulled outside >> Vdd and Vss). > > No problem. Older 4k cmos would latch up and short the supply if you > transiently forward-bias an ESD diode, which gets worse at high supply > voltages. Maybe watch out for that, with the unusual supplies. > >
Thanks.
Reply by Pimpom April 17, 20202020-04-17
On 4/17/2020 6:14 PM, Clive Arthur wrote:
> On 17/04/2020 12:12, Pimpom wrote: >> I'm designing an analog circuit with a regulated +/-12V supply. I want >> to include a 4000 series CMOS logic device to switch a sub-circuit at >> sub-Hz frequency. >> >> I haven't worked out all the details but, at this stage, using ground as >> Vdd and -12V as Vss looks like a convenient way to go. Is there any >> reason why this is inadvisable? Any caveats? (Proper care will be taken >> to ensure that no pin will be pulled outside Vdd and Vss). > > I've done this, no problems at all except make sure it's *very* clearly > marked on the circuit diagram for the repair technician. >
Noted, and thanks. I'm not sure yet if this will go into production.
Reply by April 17, 20202020-04-17
On Fri, 17 Apr 2020 16:42:17 +0530, Pimpom <nobody@nowhere.com> wrote:

>I'm designing an analog circuit with a regulated +/-12V supply. I >want to include a 4000 series CMOS logic device to switch a >sub-circuit at sub-Hz frequency. > >I haven't worked out all the details but, at this stage, using >ground as Vdd and -12V as Vss looks like a convenient way to go. >Is there any reason why this is inadvisable? Any caveats? (Proper >care will be taken to ensure that no pin will be pulled outside >Vdd and Vss).
No problem. Older 4k cmos would latch up and short the supply if you transiently forward-bias an ESD diode, which gets worse at high supply voltages. Maybe watch out for that, with the unusual supplies. -- John Larkin Highland Technology, Inc Science teaches us to doubt. Claude Bernard
Reply by Clive Arthur April 17, 20202020-04-17
On 17/04/2020 12:12, Pimpom wrote:
> I'm designing an analog circuit with a regulated +/-12V supply. I want > to include a 4000 series CMOS logic device to switch a sub-circuit at > sub-Hz frequency. > > I haven't worked out all the details but, at this stage, using ground as > Vdd and -12V as Vss looks like a convenient way to go. Is there any > reason why this is inadvisable? Any caveats? (Proper care will be taken > to ensure that no pin will be pulled outside Vdd and Vss).
I've done this, no problems at all except make sure it's *very* clearly marked on the circuit diagram for the repair technician. -- Cheers Clive
Reply by Pimpom April 17, 20202020-04-17
I'm designing an analog circuit with a regulated +/-12V supply. I 
want to include a 4000 series CMOS logic device to switch a 
sub-circuit at sub-Hz frequency.

I haven't worked out all the details but, at this stage, using 
ground as Vdd and -12V as Vss looks like a convenient way to go. 
Is there any reason why this is inadvisable? Any caveats? (Proper 
care will be taken to ensure that no pin will be pulled outside 
Vdd and Vss).