reg + reference
in [Design]
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From: Spehro Pefhany on 28 Mar 2010 18:59 On Sun, 28 Mar 2010 14:14:49 -0800, the renowned "Artemus" <bogus(a)invalid.org> wrote: > >"John Larkin" <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote in message >news:8sdsq5h1eaastj51m4ter75ido4npmp1i4(a)4ax.com... >> On Fri, 26 Mar 2010 13:43:32 -0800, "Artemus" <bogus(a)invalid.org> >> wrote: >> >> > >> >"John Larkin" <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote in message >> >news:13rpq5lqd1lj1k9flb9orfr2vcl2tuucpi(a)4ax.com... >> >> >> >> ftp://jjlarkin.lmi.net/V220_reg.JPG >> >> >> >> >> >> John >> >> >> > >> >How much current can that 1117 source from it's ADJ pin? >> >Art >> > >> >> Oh, I see what you're getting at, fig 4 >> >> ftp://jjlarkin.lmi.net/ARM_power.JPG >> >> if I catch your drift. Nice. >> >> John > >Just a silly comment re the labeling of the pins of the 1117 in your >dwg. >Art LOL. Didn't even notice that. I tend to swap digits in long incomprehensible part numbers when I'm tired & in a rush. Best regards, Spehro Pefhany -- "it's the network..." "The Journey is the reward" speff(a)interlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com
From: John Larkin on 29 Mar 2010 12:56 On Sun, 28 Mar 2010 18:02:46 +0100, "markp" <map.nospam(a)f2s.com> wrote: > >"John Larkin" <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote in message >news:uddsq5ldu791ingq021n2fik76mic9taj4(a)4ax.com... >> On Sat, 27 Mar 2010 07:08:36 -0700 (PDT), "langwadt(a)fonz.dk" >> <langwadt(a)fonz.dk> wrote: >> >>>On 27 Mar., 02:40, John Larkin >>><jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: >>>> On Fri, 26 Mar 2010 17:01:38 -0700 (PDT), "langw...(a)fonz.dk" >>>> >>>> >>>> >>>> <langw...(a)fonz.dk> wrote: >>>> >On 26 Mar., 22:24, John Larkin >>>> ><jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: >>>> >> On Fri, 26 Mar 2010 19:21:00 GMT, Jan Panteltje >>>snip >>>> >> Or maybe there exists a 3 volt 3-wire reference that would work from >>>> >> 3.3 volts. >>>> >>>> >use the ~3.3V as reference, measure a 1.2V reference voltage and >>>> >correct for it? >>>> >>>> I could use a 1.2 volt shunt reference, with a reasonable resistor >>>> from 3.3, and use an opamp to scale the 1.2 up to 3. More parts! The >>>> National low-dropout reference is ideal, if it doesn't oscillate. >>>> >>>snip >>> >>>I meant connect the 1.2V reference to a spare ADC channel, no scaling >>>needed. >>> >>> >>>-Lasse >> >> Oh. Then we'd use 3.3 as the ADC reference, measure 1.2, and normalize >> measured values against the 1.2. That would work, with a bit more >> math... unfortunately a divide, but not too often. I could do that at >> 2.5 volts, too, and still have a reasonable voltage drop across a >> resistor to 3.3. Nice idea. >> >> John >> > >Except that these 'voltage refrences' are normally bandgap references, very >stable over temperature and voltage but have low accuracy in absolute terms. >You'll need to calibrate it to get any decent absolute accuracy. > >Mark. > We will have to calibrate each channel. My target is 0.1% accuracy, and I'll be buying lots of 1% sorts of parts. The big concern is TC. The LM4040-3.0 that we have in stock is spec'd at 150 PPM max, with a typical of 15! I think somebody, Analog maybe, may make better 2-terminal bandgaps. John
From: John Larkin on 29 Mar 2010 13:07 On Sun, 28 Mar 2010 18:18:01 +0100, "markp" <map.nospam(a)f2s.com> wrote: > >"John Larkin" <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote in message >news:63ksq59j6m3u6hqnboijnngb5qqi52fbf5(a)4ax.com... >> On Sat, 27 Mar 2010 10:58:04 -0700, Joerg <invalid(a)invalid.invalid> >> wrote: >> >>>John Larkin wrote: >>>> On Sat, 27 Mar 2010 08:47:41 -0700, Joerg <invalid(a)invalid.invalid> >>>> wrote: >>>> >>>>> John Larkin wrote: >>>>>> On Fri, 26 Mar 2010 17:22:36 -0700, Joerg <invalid(a)invalid.invalid> >>>>>> wrote: >>>>>> >>>>>>> John Larkin wrote: >>>>>>>> On Fri, 26 Mar 2010 15:36:09 -0700, John Larkin >>>>>>>> <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >>>>>>>> >>>>>>>>> On Fri, 26 Mar 2010 14:34:19 -0700, Joerg <invalid(a)invalid.invalid> >>>>>>>>> wrote: >>>>>>>>> >>>>>>>>>> John Larkin wrote: >>>>>>>>>>> ftp://jjlarkin.lmi.net/V220_reg.JPG >>>>>>>>>>> >>>>>>>>>> Just curious, why not replace all this with one of these: >>>>>>>>>> >>>>>>>>>> http://www.analog.com/static/imported-files/Data_Sheets/ADR01_02_03_06.pdf >>>>>>>>>> >>>>>>>>>> Much less space, cheaper. Unless you need the 3.3V somewhere. >>>>>>>>> Yes, I need 3.3 to run an ARM processor, 40 mA or so maybe. >>>>>>>>> >>>>>>>>> The ADR could run off the +15, so maybe that's a better way to go. >>>>>>>>> It >>>>>>>>> would cost a little more, but the TC would be a lot better. >>>>>>>>> >>>>>>>>> Maybe I'll do that, the LM1117 for power and the ADR for the >>>>>>>>> reference. >>>>>>>>> >>>>>>>>> Wait! LM4120 will work. +3 ref with 120 mV dropout! >>>>>>>>> >>>>>>>>> >>>>>>>>> John >>>>>>>> And of course, the LM4120 is a stability land-mine of its own. >>>>>>>> >>>>>>>> ThestandardapplicationcircuitfortheLM4120isshownin >>>>>>>> Figure1.Itisdesignedtobestablewithceramicoutput >>>>>>>> capacitorsintherangeof0.022�Fto0.047�F.Notethat >>>>>>>> 0.022�Fistheminimumrequiredoutputcapacitor.These >>>>>>>> capacitorstypicallyhaveanESRofabout0.1to0.5. >>>>>>>> SmallerESRcanbetolerated,howeverlargerESRcannot. >>>>>>>> Theoutputcapacitorcanbeincreasedtoimproveloadtran- >>>>>>>> sientresponse,uptoabout1�F.However,valuesabove >>>>>>>> 0.047�Fmustbetantalum.Withtantalumcapacitors,inthe >>>>>>>> 1�Frange,asmallcapacitorbetweentheoutputandthe >>>>>>>> referencepinisrequired.Thiscapacitorwilltypicallybein >>>>>>>> the50pFrange.Caremustbetakenwhenusingoutput >>>>>>>> capacitorsof1�Forlarger.Theseapplicationmustbethor- >>>>>>>> oughlytestedovertemperature,lineandload. >>>>>>>> >>>>>>>> >>>>>>>> Thanks, National. >>>>>>>> >>>>>>> I was just gonna tell you. If there was one I'd have a bumper sticker >>>>>>> on >>>>>>> my car "LDO, no, no, no!" >>>>>>> >>>>>>> My advice to clients there is always the same, don't ever use an LDO >>>>>>> unless there is absolutely no other way (and in my 25 years on the >>>>>>> beat >>>>>>> there always was). No matter what the marketeers sing from the trees. >>>>>> Unless I work off the +15, which has its own complications, I need >>>>>> this LDO voltage reference. After all, they say it's stable over - >>>>>> wait for it - a 2:1 load capacitor range! Assuming you get the ESR >>>>>> right. >>>>>> >>>>> And nothing seems to be guaranteed. When I read page 9 in the datasheet >>>>> I am beginning to feel sick. >>>> >>>> Cute, how they say the compensation capacitor is in the "50 pF range" >>>> and how they expect *me* to compensate and extensively >>>> temperature/line/load test *their* part to ensure stability. I'm >>>> expected to do a couple thousand dollars worth of testing on their >>>> behalf. >>>> >>>> National is very sloppy as regards stability of lots of their parts. >>>> >>> >>>Which is why I haven't designed in any of their power parts lately, >>>except legacy stuff such as the LM317. LTC is pretty good, very >>>responsive, great support engineers who really know electronics. Plus >>>LTSpice models for just about anything and that alone ist worth a ton, >>>has won them many design-ins on my part. Although I recently unearthed >>>an ugly power-up bug in a part but that was a comparator, LT6700. But >>>they went to the ground of it, confirmed it, fessed up, and apologized. >>>Way to go. >> >> >> Yes, LTC is great. And LT Spice is a gift to the world. >> >> >>> >>>> >>>>> Why does working off of the +15V have complications? >>>> >>>> I'd need a series reference that can tolerate unregulated +15, so I'd >>>> probably have to preregulate into it... more parts. Shunt regs have >>>> mediocre TCs and would get not-very-constant current if I just use a >>>> resistor from +15. I expect that my 4-20 mA (really 0 to 25 maybe) >>>> load and uP power patterns will whack the DC-DC output voltage all >>>> over the place. >>>> >>>> There will be 12 channels per VME board, so I want low parts count and >>>> cheap parts! >>>> >>> >>>An RC filter or capacitor multiplier should suffice. Input ripple >>>rejection is usually huge as long as it doesn't contain high frequency >>>stuff. Or use one preregulator per board. Or even better, one reference >>>per board. >> >> >> Sadly, all 12 channels are individually floating. >> >> It's looking like the safest thing to do is use an LM1117 to make >> about 3.4 volts - close enough to 3.3 - and use a ca 500 ohm resistor >> into an LM4040-3.0 or equivalent bandgap with a 10 uF ceramic bypass. >> Typical TC will be about 15 PPM (guaranteed is not as good, but not >> lethally bad), sensitivity to 1117 output is pretty good (500 ohms >> into Zd~~1 ohm), and it's simple and cheap and most important, it's >> safe. >> >> That out of the way, my next task is to explode some SSRs. Certain >> user abuse modes will put, say, 50 volts across an ON-state SSR. The >> ARM will sense the hazard and turn off the SSR, so it will have to >> tolerate the abuse for a millisecond maybe. I'm considering some Clare >> 8-ohm, 100 volt, 150 mA parts. So what happens if you turn them on and >> put a bunch of voltage across them? >> >> I love to test parts to destruction. >> >> John >> > >1% tolerance is pretty bad for a precision reference. Here's a better one: >http://www.farnell.com/datasheets/71410.pdf > >Not avaialble at 3V unfortunately, but +/-1mV at 2.5V is 0.04%! 20ppm per >deg C temperature coefficient max. > >Mark. > Tolerance doesn't matter, as we'll be calibrating channels. The low TC is appealing. Those floating-gate things are interesting, and I could run the ADC ref at 2.5 volts, but their dynamics looks goosey. Too big a risk for me on this project. John
From: markp on 29 Mar 2010 13:11 "John Larkin" <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote in message news:vmm1r59d7op7lbvlfkjmckprjgji43huvm(a)4ax.com... > On Sun, 28 Mar 2010 18:02:46 +0100, "markp" <map.nospam(a)f2s.com> > wrote: > >> >>"John Larkin" <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote in >>message >>news:uddsq5ldu791ingq021n2fik76mic9taj4(a)4ax.com... >>> On Sat, 27 Mar 2010 07:08:36 -0700 (PDT), "langwadt(a)fonz.dk" >>> <langwadt(a)fonz.dk> wrote: >>> >>>>On 27 Mar., 02:40, John Larkin >>>><jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: >>>>> On Fri, 26 Mar 2010 17:01:38 -0700 (PDT), "langw...(a)fonz.dk" >>>>> >>>>> >>>>> >>>>> <langw...(a)fonz.dk> wrote: >>>>> >On 26 Mar., 22:24, John Larkin >>>>> ><jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: >>>>> >> On Fri, 26 Mar 2010 19:21:00 GMT, Jan Panteltje >>>>snip >>>>> >> Or maybe there exists a 3 volt 3-wire reference that would work >>>>> >> from >>>>> >> 3.3 volts. >>>>> >>>>> >use the ~3.3V as reference, measure a 1.2V reference voltage and >>>>> >correct for it? >>>>> >>>>> I could use a 1.2 volt shunt reference, with a reasonable resistor >>>>> from 3.3, and use an opamp to scale the 1.2 up to 3. More parts! The >>>>> National low-dropout reference is ideal, if it doesn't oscillate. >>>>> >>>>snip >>>> >>>>I meant connect the 1.2V reference to a spare ADC channel, no scaling >>>>needed. >>>> >>>> >>>>-Lasse >>> >>> Oh. Then we'd use 3.3 as the ADC reference, measure 1.2, and normalize >>> measured values against the 1.2. That would work, with a bit more >>> math... unfortunately a divide, but not too often. I could do that at >>> 2.5 volts, too, and still have a reasonable voltage drop across a >>> resistor to 3.3. Nice idea. >>> >>> John >>> >> >>Except that these 'voltage refrences' are normally bandgap references, >>very >>stable over temperature and voltage but have low accuracy in absolute >>terms. >>You'll need to calibrate it to get any decent absolute accuracy. >> >>Mark. >> > > We will have to calibrate each channel. My target is 0.1% accuracy, > and I'll be buying lots of 1% sorts of parts. The big concern is TC. > The LM4040-3.0 that we have in stock is spec'd at 150 PPM max, with a > typical of 15! I think somebody, Analog maybe, may make better > 2-terminal bandgaps. > > John Well as i noted in another post 1% tolerance is pretty bad for a precision reference. Here's a better one: http://www.farnell.com/datasheets/71410.pdf Not avaialble at 3V unfortunately, but +/-1mV at 2.5V is 0.04%! 20ppm per deg C temperature coefficient max. Mark.
From: JW on 30 Mar 2010 05:20
On Mon, 29 Mar 2010 09:56:45 -0700 John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote in Message id: <vmm1r59d7op7lbvlfkjmckprjgji43huvm(a)4ax.com>: >On Sun, 28 Mar 2010 18:02:46 +0100, "markp" <map.nospam(a)f2s.com> >wrote: > >> >>"John Larkin" <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote in message >>news:uddsq5ldu791ingq021n2fik76mic9taj4(a)4ax.com... >>> On Sat, 27 Mar 2010 07:08:36 -0700 (PDT), "langwadt(a)fonz.dk" >>> <langwadt(a)fonz.dk> wrote: >>> >>>>On 27 Mar., 02:40, John Larkin >>>><jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: >>>>> On Fri, 26 Mar 2010 17:01:38 -0700 (PDT), "langw...(a)fonz.dk" >>>>> >>>>> >>>>> >>>>> <langw...(a)fonz.dk> wrote: >>>>> >On 26 Mar., 22:24, John Larkin >>>>> ><jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: >>>>> >> On Fri, 26 Mar 2010 19:21:00 GMT, Jan Panteltje >>>>snip >>>>> >> Or maybe there exists a 3 volt 3-wire reference that would work from >>>>> >> 3.3 volts. >>>>> >>>>> >use the ~3.3V as reference, measure a 1.2V reference voltage and >>>>> >correct for it? >>>>> >>>>> I could use a 1.2 volt shunt reference, with a reasonable resistor >>>>> from 3.3, and use an opamp to scale the 1.2 up to 3. More parts! The >>>>> National low-dropout reference is ideal, if it doesn't oscillate. >>>>> >>>>snip >>>> >>>>I meant connect the 1.2V reference to a spare ADC channel, no scaling >>>>needed. >>>> >>>> >>>>-Lasse >>> >>> Oh. Then we'd use 3.3 as the ADC reference, measure 1.2, and normalize >>> measured values against the 1.2. That would work, with a bit more >>> math... unfortunately a divide, but not too often. I could do that at >>> 2.5 volts, too, and still have a reasonable voltage drop across a >>> resistor to 3.3. Nice idea. >>> >>> John >>> >> >>Except that these 'voltage refrences' are normally bandgap references, very >>stable over temperature and voltage but have low accuracy in absolute terms. >>You'll need to calibrate it to get any decent absolute accuracy. >> >>Mark. >> > >We will have to calibrate each channel. My target is 0.1% accuracy, >and I'll be buying lots of 1% sorts of parts. The big concern is TC. >The LM4040-3.0 that we have in stock is spec'd at 150 PPM max, with a >typical of 15! I think somebody, Analog maybe, may make better >2-terminal bandgaps. > >John Haven't been following this thread too closely, but these look like pretty nice references and may be of use: http://www.analog.com/en/references/voltage-references/adr423/products/product.html |