LT1021 plastic - Page 1
Forum section: electronics / general

author: GigaJoe
author_rank: Frequent Contributor
timestamp: April 30, 2023, 04:35:14 pm
content: im going cheap, as usual ...a while ago i did 16 plastic LT1021, paralleling together over some balancing resistors, with adjustment and inside a thermostat.As the thermostat itself are good, all this construction became a bit better than disaster, an output swing at non predicted level, randomly going up and down.Im goin to the next loop of cheapso i pick random used LT1021-10 PDIP8 , add basic china multiturn resistor, 1N4148 as compensation, from +20C to +40C , i got negative swing of 4 microvolts. basically lucky. tossed in plastic container, add 2 5W resistors, container filled by oil , everything in a thermos. basic 12V regulatorit run it some period on March, (let say 500 hours) ; and on april I sporadically did a measurement , just to see a tendency .. ; measurement device 34401a , with positive tempco, and room temp usually +18, and was +20 during mid April heatwave.im guesin - 4 (or 6) such modules , adjusted to min tempco , a bit running a couple month ,then adjusted to the same output , (avoiding balancing resistors) probably make sense.attached file of sporadic measurement, and guessing Temp inside of oil bottle as thermistor not calibrated. 34401a I think +0.8PPM

author: iMo
author_rank: Super Contributor
timestamp: April 30, 2023, 06:06:51 pm
content: Interesting.. Mind the measurement with 34401A is tricky, from my experience.. It needs 8-12h to fully stabilize and its TC depends on elapsed time after the power-on. A measurement here takes a day..I collected around 40pcs of epoxy 1021-10 and -5, their TC -1 to +4ppm (simple finger method). The idea with the oil is interesting. Perhaps I would dry the epoxy first and then put the package(s) into the oil, the oil should not be hygroscopic.Why do your temperature in the thermos flask vary so much (3C)?

author: GigaJoe
author_rank: Frequent Contributor
timestamp: April 30, 2023, 07:15:11 pm
content: multimeter are constantly on , 2 years maybe ... switching display off . had some fun with insulate LM , add some shields, maximum possible filter caps, add some poly on top of tantalum. switch back\frond - soldered ; kinda modding does it helps no idea.the temperature not stabilized, just 2 resistors , so it depend on ext. temp. and i think i stacked something on top , so temp dissipation does lower and temp, increased.the lowest air room temp around +17 highest maybe 20-21 , in a month period. I'm really have no idea why i add non stabilized heater, guess it was assumption it smooth deviation, it probably can , but need carefully build a carrying case so excess power dissipation need more less constant.im quite satisfied , had assumption it would much worse. LT1021 I actually pick with really high tempco like 20ppm , so ruthlessly fire it up , but it works, I add 5 diodes to compensate tempco . I have an idea to add diodes till temco change sign, then add something ( potentiometer , something else) to the last diode for adjusting the level how this diode will affect tempco.

author: GigaJoe
author_rank: Frequent Contributor
timestamp: August 07, 2023, 02:23:21 am
content: 20230502 9.99984320230806 9.999750

author: iMo
author_rank: Super Contributor
timestamp: August 07, 2023, 07:21:05 am
content: Yep, I still wonder how it is possible people so often report "great" results from their cheapo 1021 based calibrators..Afaik Andreas and dietert1 reported good results when keeping the 1021 at elevated temperatures - like 50C and 42C, and 24x7 powered on.

author: Andreas
author_rank: Super Contributor
timestamp: August 07, 2023, 06:26:15 pm
content: Quote from: GigaJoe on August 07, 2023, 02:23:21 amHmm, I am missing at least temperature (and humidity for the plastic case).Quote from: iMo on August 07, 2023, 07:21:05 amNo I do not have a LT1021 under observation.The only part (in SO-8) has about 7 ppm/K temperature drift.So I use it for ratiometric (temperature) measurements.As all buried zeners the LT1021 has a low ageing drift.For the T.C. they should be temperature stabilized.Against humidity one would use the metal can version.with best regardsAndreas

author: iMo
author_rank: Super Contributor
timestamp: August 07, 2023, 06:37:03 pm
content: Quote from: Andreas on August 07, 2023, 06:26:15 pmAhh, my bad, I've thought those are the plastic 1021https://www.eevblog.com/forum/metrology/small-oven-controler-for-voltage-reference/msg1655015/#msg1655015

author: Andreas
author_rank: Super Contributor
timestamp: August 07, 2023, 07:13:31 pm
content: Hello,No those are now mostly AD586LQ CERDIP8 after replacing the formerly LT1027 (DIP8).Some MAX6250A, MAX6350, one LT1019, one REF102AP, one AD586MNZ (in PDIP)and finally some LT1236AILS-8with best regardsAndreas

author: GigaJoe
author_rank: Frequent Contributor
timestamp: August 08, 2023, 03:29:22 am
content: it cheap plastic ... random taken, usedit thermally compensated. by diodes , approx -0.1-0.2 ppmin oil bath , and heater , non-thermostatic, around +45Ceverything in a plastic container, container in a metal thermos.sooo. basically humidity irrelevant, temp ... maybe ... im curious how it goes ... will see in next few month ...

author: GigaJoe
author_rank: Frequent Contributor
timestamp: February 29, 2024, 02:22:54 am
content: 20230502 9.99984320230806 9.99975020240228 9.999792no comments ...

author: magic
author_rank: Super Contributor
timestamp: February 29, 2024, 06:17:13 am
content: As far as I understand, it should be possible to null linear TC of most LT1021 specimens with a pot between pins 1,8 with grounded wiper. Or fixed resistor(s). The external network will be in parallel with two factory trimmed on-chip resistors of a few kΩ each, so its resistance should be fairly high for low sensitivity. This adjustment affects output voltage too.Maybe better than compensation with external diodes?

author: iMo
author_rank: Super Contributor
timestamp: February 29, 2024, 06:49:17 am
content: Do we know how the pins 1 and 8 are wired internally? (NC in the DS).Perhaps this -https://www.eevblog.com/forum/metrology/decapping-the-lt1236ls8/msg2935094/#msg2935094

author: Andreas
author_rank: Super Contributor
timestamp: February 29, 2024, 07:01:40 am
content: Mhm,does this work with LT1236 too?The chips look very similar.with best regardsAndreas

author: magic
author_rank: Super Contributor
timestamp: February 29, 2024, 07:16:14 am
content: Yes, this is what I meant.Quote from: Andreas on February 29, 2024, 07:01:40 amIIRC we couldn't find any difference betweenLT1021-5andLT1236, other than different package and maybe different factory trimming.LT1021-10has the same adjustment network on pins 1,3,7,8 wired to the current mirror of its internal opamp.

author: iMo
author_rank: Super Contributor
timestamp: February 29, 2024, 07:25:29 am
content: But there are the 4 fuses (shorting the resistors) between pins 1/3/7/8, so it depends, whether it is possible or not..Or, do blow up the fuses and then you may play with the balancing as you wish..PS: I see only 2 fuses blown up in my 10 random 1021 samples (out of 37)..

author: iMo
author_rank: Super Contributor
timestamp: February 29, 2024, 10:56:34 am
content: I've set my PSU to 2V/50mA and I've tried to blow up the 4 fuses (all 4 were active/short in this 1021-5 sample).Now I see aprox 2.5k\$\Omega\$ between pin8 and pin7 and between pin1 and pin3.Still short between pin7 and gnd and between pin3 and gnd, however.PS: With a little bit more voltage I blew up the 7-gnd and 3-gnd fuses as well.8-7 aprox 2.57k\$\Omega\$7-gnd aprox 1.31k\$\Omega\$1-3 aprox 2.55k\$\Omega\$3-gnd aprox 1.95k\$\Omega\$8-gnd aprox 30.6mV7-gnd aprox 10.5mV3-gnd aprox 15.5mV1-gnd aprox 34.4mV

author: iMo
author_rank: Super Contributor
timestamp: March 02, 2024, 08:11:25 am
content: FYI- With an 1k 10T WW pot wired between pin8 and pin1 (wiper to gnd) I can set the output voltage aprox -5mV..+4mV around the 5.000V. The TC is always positive in that range, perhaps a little bit lower in the "middle", however..That is why most samples have their 4 fuses active (a short).

author: ru_tash
author_rank: Regular Contributor
timestamp: March 12, 2025, 10:22:03 am
content: Quote from: iMo on February 29, 2024, 10:56:34 amI blew them up with 1.7 amps (3V)

author: CalibrationGuy
author_rank: Unknown
timestamp: March 13, 2025, 02:32:03 am
content: The $10,000.00+ Fluke 754 calibrator uses a metal can LT1021 (actually 3, I think). I saw them when I was replacing a damaged LCD. The 754's performance is excellent, its my favorite field instrument.TomG.

author: GigaJoe
author_rank: Frequent Contributor
timestamp: March 28, 2025, 02:42:22 am
content: Finally, what i made , DIP8 soldered on 2 pins +V and ground, then it was trimmed by diodes to as low as possible tempco in range 20-40Cvery small Styrofoam box and chip inside this box, then i use aluminum sticky tape for waterproof application, and made 2 layers around styrofoam box. then another Styrofoam box and again 2 layers of aluminum foil. basic psu and left it as is since beginning of last year ...then i realize that my instrument has very Hight tempco. all i can use to reasonable measure, are one of 3456a that has just +3 PPM cold\hot deviation. ( best of all my collection)before December number and overall measurement wasn't good enough ... Chip are on UPS all time, i cycled it twice, and it drop to -2ppm then restored back in the a 2-3 weeks.in the middle of December the last digit was 6 , February 7 , now 8 (sometime 9) maybe i can say it drifting to +10 to +12 PPM per year.so this is plastic, reclaimed , non selected chip ....I assume metal would be better , but i'm wondering about plastic performance in overall.

author: Andreas
author_rank: Super Contributor
timestamp: March 28, 2025, 05:11:40 am
content: Quote from: GigaJoe on March 28, 2025, 02:42:22 amHello,I am usually only soldering the GND Pin into PCB (mainly for the temperature sensor which is connected also to GND).The remaining pins are soldered with thin Vero Wire.My experiences with LT DIP 8 packages (with a LT1027) are 1-2 ppm ageing drift per year and ~0.5ppm per % rH (so ~12 ppm annual change at my location)The problem is the long time constant of 4-7 days for rH (which might be longer in your case due to aluminium tape). So correlation is not easy.2 AD586MNZ in DIP8 show ~0.5 ppm/year ageing (perhaps somewhat less) and 0.4 ppm per %rH with 2-3 days time constant.But of course the plastic behaviour may vary from lot to lot if the manufacturer finds a cheaper epoxy ...with best regardsAndreas

author: iMo
author_rank: Super Contributor
timestamp: August 07, 2025, 08:25:30 am
content: Quote from: iMo on March 02, 2024, 08:11:25 amWhile in decision whether to scrap my first reference built long time back around 2x plastic LT1021-10 (plus a ceramic OP07, being ref1 9.995 with positive TC and ref2 with 10.030 with negative TC) - because its large hysteresis, I started to experiment with "flashing" the fuses of the ref2 chip. I did flash off two fuses - between pins 7-8 and 3-4. It gave me the same voltage, therefore I then shorted 7-8 externally, which moved it down by aprox 15mV. After a TC test I saw a pretty large TC, however, so the flashing did not help much.Next day I did measure the flashed ref2 chip again and all fuses looked as "not flashed" with low resistance, like 20-30ohm, but the voltage remained lowered..I took the old LT1021-5 I flashed 2y back above and it was dead (output 0.13V, but the resistances between pins were measurable as above).So a note of caution - flashing the fuses may destroy the chip - perhaps the explosion on the die causes some pressures and or contamination inside the package. Perhaps the current (~energy) used for flashing a fuse is somehow critical.I replaced the ref2 chip with a different one (in a precison socket, so not an ideal situation) and get 10.004V in the result with some positive TC, now I am baking the entire board in a pot, let us see the results then..Below the baking setup - the brown river rock comes from Urubamba river and the gray one I fished off the Bagmati river - and the temperature inside beneath the pcb is aprox 85C. I will keep that for couple of hours and let it slowly cool off afterwards..

author: iMo
author_rank: Super Contributor
timestamp: August 07, 2025, 05:58:56 pm
content: FYI - after 2.5hours in the pot the temperature inside (beneath the pcb) achieved a stable aprox 100C, so in the 3rd hour I switched off the heater, isolated entire pot thermally and let cool it down sliowly. After the next 5.5hours when the temperature dropped to aprox 40C I put the board off the pot and after short (aprox 3min long) inspection I put it into its box (also thermally isolated) and I started an overnight measurement.Btw., 2hours after the measurement started the voltage was by 450uV lower than before the burn-in..Note: The trimmer on the board was disconnected in past.

author: iMo
author_rank: Super Contributor
timestamp: August 08, 2025, 06:03:21 pm
content: .. and what the plastic did - the first graph starts 2hours after putting the pcb off the pot (the first 2hours was a steep drop while the pcb cooled fully off - I cut it off), you may see the steady voltage drop for 11hours, the drop is not related to the TC as the 7ppm/C would be too much, it is caused by the relaxation after the baking.In the second graph you may see the continuation of the measurement starting 40min later - a 12h long with the Vref within 1.2ppm, with perhaps 1-2ppm/C TC.. Let us wait for 1 month with the ref powered off, what the plastic will make..Note: voltage in the graphs is smoothed..PS: there are cutouts in the pcb around the LT1021 chips, as well as around the mounting holes..

author: GigaJoe
author_rank: Frequent Contributor
timestamp: August 11, 2025, 01:10:09 am
content: i have powered my about year and half , it settle a bit last October was more less stable all winter , around 2ppm floating ... and sharply drop in June , in 2-3 weeks when temperature outside became +30 with rain , drop approx 10ppm ( humidify changes from 45 to 60-70 , according my tabletop thermometer ) , my guess , probably humidity reach plastic encapsulation, even as much as i did try to shield it , As well i may assume humidity \ temperature affected stack of my 3456 , as before "drop" they blinking in sync , now 3 ppm difference, ( actually 2 of 4 , the rest 2 kind of no so much are team members )thinking glass can with oil .... will see ... ( kind of disappointed , i expected a less deviation .. )

author: iMo
author_rank: Super Contributor
timestamp: August 11, 2025, 10:56:55 am
content: As was discussed here in past - I had a conversation with DaliborF who is manufacturing the nixies tubes (in Czechia) on whether he can encapsulate an electronics into such a tube. He answered me it is basically doable, what need to be considered is a) the high temperature during manufacturing (that could be mitigated by a longer tube such the flame will be of some distance off the electronics), b) the vacuum level will be worse compared to the nixies (no problem with us), c) the wires used are somehow special (but it could be done).That is perhaps the only solution with the plastics and similar - baking them and then encapsulating into the vacuum tube.On the other hand such a vacuum experiment may easily cost you an arm and a leg, thus at the end of the day building three LTZ1000 based references might be a much much cheaper solution..PS: Dalibor's page -https://www.daliborfarny.com/

author: GigaJoe
author_rank: Frequent Contributor
timestamp: August 11, 2025, 01:53:36 pm
content: noo .. not that way ... this is bottom line extra low budget to squeeze max from used 50 cents chip .. so far i see no more then 20ppm per year including measurement errors ..

author: Andreas
author_rank: Super Contributor
timestamp: August 11, 2025, 02:07:51 pm
content: On LT1027 (DIP8 package) I measured on 2 samples 0.5 ppm per % relative humidity. (summer + winter)-> 10 ppm for 20% rH change sounds reasonable.The bad news is: there is a rather long time constant of several days up to one week until you see the drift on a rH change.with best regardsAndreas

author: GigaJoe
author_rank: Frequent Contributor
timestamp: August 11, 2025, 03:09:29 pm
content: the chip with board in Styrofoam box ,covered by 2 layers of construction HVAC aluminum tape, then another Styrofoam box , and another 2 layers of alu tape ...i hope it set a barrier , probably up to some degree ... it maybe well 3456A affected by temp and hymi ... the bad thing i don't have a reference as a reliable base point to figure out ... should make one

author: guenthert
author_rank: Frequent Contributor
timestamp: August 12, 2025, 11:16:41 am
content: Quote from: GigaJoe on August 11, 2025, 03:09:29 pmHmmh, I'm not quite convinced, albeit I admit, I know next to nothing about humidity affecting semiconductors. I thought submerging it in silicon oil would be a safer bet on keeping water out.Quote from: GigaJoe on August 11, 2025, 03:09:29 pmThe 3456A sure has a tempco, but that should only be some 1ppm/K around comfortable temperatures. Not sure about its sensitivity to humidity (it's reference shouldn't be), but since it runs rather warm, that should be low, if you keep it running.

author: AnalogTodd
author_rank: Regular Contributor
timestamp: August 12, 2025, 01:52:52 pm
content: Quote from: guenthert on August 12, 2025, 11:16:41 amThe semiconductor itself isn't affected by the humidity per se. Instead, it's the plastic package that takes up the moisture and swells, putting stress on internal metal die attach points and the silicon itself. Stress affects the silicon crystal and can shift reference voltages a small amount. Silicon oil does not necessarily keep moisture out (check what you are using to see if it has any info on absorbing moisture from air), it is best for maintaining a constant temperature with its good thermal conductivity.Quote from: guenthert on August 12, 2025, 11:16:41 amThe same humidity that affects the reference above may be affecting the internal reference of the 3456A based on what it is using for its internal reference.Remember, something being warm/hot does not mean low humidity. Go to Phoenix, Arizona and you'll experience 100+ deg. F days that feel plenty hot but aren't oppressively hot. Then head into the deep south and those same temperatures will wipe you out quickly. All because of a difference in humidity.

author: iMo
author_rank: Super Contributor
timestamp: August 12, 2025, 02:03:39 pm
content: Those epoxy packages contain around 5% of water (like a sponge). To get it out you need day or two at 150C, people say. If you mess with large and costly flat-packs (like 100 or 144pins) you may find inside the box with the chip a written note saying something like "before soldering please bake it for XX hours at XXX degC, otherwise the package may crack..".PS: almost all time you find inside the bag with chips a humidity indicator with colored circles..

author: GigaJoe
author_rank: Frequent Contributor
timestamp: August 12, 2025, 05:30:58 pm
content: this one one of my good one 3456A , runaway from cold to hot\running just +4 PPM, but it not nulling req. to compare it with some great standalone reference ...

author: exe
author_rank: Unknown
timestamp: August 12, 2025, 05:56:45 pm
content: I've seen entire pcbs covered with "conformal coating", though I don't like it as it makes repair a mess. But that should fix humidity problem if done properly, imo.

author: GigaJoe
author_rank: Frequent Contributor
timestamp: August 12, 2025, 08:52:45 pm
content: I had to dig deeply in context of penetrating materials by water molecules around 10y ago. So in overall .. all this humiseal ,etc coating do not prevent water molecules entering to protected object if material of the object allow to do so ...in other word , it not protecting at 100% , simply slowing down from 100% to 10-20% depend on coating thickness etc , mostly it prevent corrosion or circuit short during condensation time or accident contamination by water. And the only 100% protection are metal foil at specific thickness , and it 100% non penetrable. ( glass or other material not handy , or drop simply in glass bottle, it pass over the seal, so need a fill by material that will not accept water molecules absorption. )my own experiment with different coating ,up to multilayer 3mm polyurethane , still indicated that 3mm penetrated by water molecules , in 4 days at +35C 100% RH , DIP-8 reference starting to drift , and kind of wildly in 2 weeks , removed from chamber and it drifting back to approx. same value in 3 weeks ...

author: guenthert
author_rank: Frequent Contributor
timestamp: August 13, 2025, 09:54:25 am
content: Quote from: AnalogTodd on August 12, 2025, 01:52:52 pmWell, most 3456A use a -hp- branded (surely selected) LMx99 (very early ones might have a different reference?) in a metal can, not prone to absorption. How much the entire circuit is affected, I wouldn't know. -hp- didn't specify a dependency, just a (generous) max. rel. humidity.Quote from: AnalogTodd on August 12, 2025, 01:52:52 pmUh, a surface warmer than the surrounding air will absorb less though (opposite of condensation).

author: AnalogTodd
author_rank: Regular Contributor
timestamp: August 13, 2025, 01:44:12 pm
content: Quote from: guenthert on August 13, 2025, 09:54:25 amMetal cans are usually impervious to humidity changes, yes. Unless the glass seals are failing, which can happen over time. On top of that, what around the circuit is used to make the measurements? There's a lot of things that can come into play, and I don't have a schematic of the internals or know how each part is packaged.Quote from: guenthert on August 13, 2025, 09:54:25 amBut moisture will still be absorbed into the plastic. I worked at a major semiconductor manufacturer for decades and discussed reference voltage shifts with some of the best in the industry. We could keep a reference (in plastic package) at the same temperature (usually within 1 deg. C of setpoint) and watch the reference shift over time matching the relative humidity of the room (the chamber kept ambient air from the room circulating in it). Where I live now, we have very high RH in the summer months, so much so that being outside on a 90F day feels like it is well over 100F and it is oppressive to be outside for long. I can contrast that with when I used to live in Silicon Valley and 100F days really weren't an issue. A reference in a plastic package going between the two places will have moisture move in and out of the plastic and shift reference values, and a change in RH wherever you are will do the same.

author: mawyatt
author_rank: Super Contributor
timestamp: August 13, 2025, 02:25:34 pm
content: We had an issue with moisture contamination back in early 70s where theSealantturned out to be the culprit. Ceramic modules were failing temperature cycling, failure wasthoughtto be bad SMD decoupling cap across the 12VDC Power Input. After digging out the sealant potting and replacing the suspect cap everything returned to normal. However the failures continued with new OEM caps, same result, so we investigated the removed failed caps, they were all fine!!Took awhile to figure out what was going on, the sealant potting was hydroscopic (everything seems hydroscopic even water/humidity sealents!!). During temp cycling the sealantpriorcaptured moisture would work it's way onto the ceramic substrate surface and mix with the residual salts left over from flux and handling. This mixture would wick under the suspect SMD cap and eventually create dendrites with the cap termination/solder and applied 12VDC Power and short across the cap. When the cap was removed the dentrites would be absorbed back into the solder without a trace.It turned out the Sealant used had been left exposed to the air, thus absorbing moisturepriorto use, then container resealed. New Sealant, better ceramic cleaning, and better handing, eliminated this problem, but this was a difficult one to eventually findBest

author: iMo
author_rank: Super Contributor
timestamp: August 13, 2025, 03:25:06 pm
content: Perhaps bake the epoxy package and while still hot put it into a sealant under vacuum, such the sealant replaces the water inside the package - just as wooden railway sleepers were once impregnated with hot tar in large vacuum chambers, afaik..

author: iMo
author_rank: Super Contributor
timestamp: September 11, 2025, 05:33:24 am
content: FYI - my above 2x LT1021 plastic 10V ref switched on after 1 month powered off on the shelf. The entire board was baked a month back as shown above.The voltage month back after the baking and before the powering off was 10.003546V (see the abovemeasurement), thus it has started aprox +45ppm higher in the below graph and slowly decreasing..Absolutely not usable for anything better than 12bit, imho.

author: Gyro
author_rank: Super Contributor
timestamp: September 11, 2025, 06:48:42 pm
content: Quote from: iMo on August 13, 2025, 03:25:06 pmHermetically sealed enclosures a still really easy to realize using thin copper sheet and soldered seams. Connections can be brought out through soldered in glass hermetic feedthroughs (or ceramic feedthrough capacitors). If you can't find those, look for an old hermetic relay on ebay and use the base. Don't forget to bring out the minimal range trimming connections for an external pot or resistor. Add a couple of thin copper or brass tubes and you can purge the enclosure with dry Nitrogen or Argon before crushing them and solder sealing the ends. Plastic packages don't necessarily need to be a problem.

author: Overspeed
author_rank: Frequent Contributor
timestamp: September 12, 2025, 07:44:52 am
content: HelloJust an ideaDoes someone have tested Ceracote coating ? curing is 2 hours at 120 deg Cfor glass sealed tube if your component is far from the end closure , temperature can be managable ? perhpas possible to use a glass milk bottle with a quite large opening ?watch this video at the end he manipulate the glass part by hand so temp shall be reasonableFor vaccum just need a small glass tube passthrough sealed after vaccum .RegardsOS

author: iMo
author_rank: Super Contributor
timestamp: September 12, 2025, 09:11:16 am
content: If somebody insists on the LT102x like references the easiest way is to buy theQuote from: iMo on March 05, 2024, 01:41:52 pmhttps://www.analog.com/media/en/technical-documentation/data-sheets/1236ls8f.pdfPS: and not soldered to the pcb but "dead bug" or "trampoline" style with thin wires.. With some TC compensation (ie. Andreas is doing long term measurements on it, afaik)..

author: CalibrationGuy
author_rank: Unknown
timestamp: September 12, 2025, 02:58:43 pm
content: Quote from: iMo on September 11, 2025, 05:33:24 amA couple of comments/observations:1) What is your measurement setup? Do you have a vfref like a 732?2) The datasheets are clear that this was for 12 bit systems, so you are correct.3) We've observed that there is a large variation in drift and stability with these parts, so we take 50 or so and pick the best ones.4) When we build a/d or vref units, the vref chip cost is only a minor consideration so we use the 1399.Still, this part is useful for a hobby type unit and it's simple to build.TomG.

author: iMo
author_rank: Super Contributor
timestamp: September 12, 2025, 05:05:42 pm
content: Quote from: CalibrationGuy on September 12, 2025, 02:58:43 pmThe setup is described in the graph above. No need to use 732 for exercises w/ LT1021, imho.. (my ref here is ADR1001#1 running for several years already..)

author: GigaJoe
author_rank: Frequent Contributor
timestamp: September 17, 2025, 05:02:16 pm
content: i'm not sure of the meaning 12-bit ... for 10V quantization 2.5mV, dont forget chip from 80x era .. 16bit adc was a rare and expensive animalsso far my data:20250328 9.9995820250604 9.9994620250917 9.99942now it measured by 4 x 3456a , so more less valid for driftingthat june was a large drop , like in approx 15 days if falls down , I assume it was summer humidity, but i'm wrong, seems my sealing work ., just some drifting ...so from june it about -1 PPM \ month.thete is no any fluctuation , as i minitored for 2 month , just slow drift down ... now simply turn on stack of dmm , wait a few days, look at numbers ...

author: iMo
author_rank: Super Contributor
timestamp: September 17, 2025, 05:12:13 pm
content: Quote from: GigaJoe on September 17, 2025, 05:02:16 pmThe Vref with 12bit ADCs in 70ties and 80ties shall drift ideally in total (short/long term, TC/humidity/hysteresis/Inp.voltage inclusive) less than a half of 1LSB.With 1LSB = 2.44mV (with 10V) that is 1.22mV, that is 122ppm (and it may fit even the plastic 1021-10, for example).

author: GigaJoe
author_rank: Frequent Contributor
timestamp: September 18, 2025, 12:40:00 am
content: btw , do you have PDF where 12bit referred .... i can not find any

author: CalibrationGuy
author_rank: Unknown
timestamp: September 20, 2025, 08:35:01 am
content: Quote from: GigaJoe on September 18, 2025, 12:40:00 amLT1236 datasheet, page 7.TomG.

author: GigaJoe
author_rank: Frequent Contributor
timestamp: September 21, 2025, 05:40:37 pm
content: QuoteOK:QuoteGuess, this particular sentence is sufficient to invalidate 12bit statement ...