Just some other notes from my experiments with 10V refs:
I have tested several LT1031 in metal case (all bought new from ELFA-Distrilec) and was not happy with them. They drifted a lot and especially nasty is that they change a lot if turned off for some weeks after being on continuously for a long time see chart in another thread.
https://www.eevblog.com/forum/metrology/new-voltage-reference-from-maxim/msg971413/#msg971413 . The strange thing is that the two LT1021 I have in metal cases (bought on eBay) are much better even if not as good as the AD587xQ for drift and long power interrupts. In my measurements with 3 weeks power off and 3h on a couple of times the AD587xQ an LT1021CMH is very little affected with less than 1 or 2 ppm , REF102CM about 3-5ppm and LT1031DMH up to 10-40 ppm. Many plastic packages also show 10-30ppm up to maybe 50ppm worst case as I have seen.
Almost all up to 1mA buried zener refs I checked has at some time jumps (pop corn noise) On some it can only be seen at some temperatures on other can be long between that is minutes, days or even months I have seen. (LM399, AD587, REF102, LT1021,1031, 1236 etc). For me it seems that about 0.8ppm jumps is very common but also 0.4 or 1.5ppm. One 6 digit DMM (with LM399) has for 20 years shown 1.5ppm jumps maybe several times per day. As others have shown even LTZ1000 might have “jumps”. So for an uncertainty analysis for 10v refs I always recommend to say 0.8ppm for jumps and also I have seen a step after months or even years of several ppm so getting below 5ppm uncertainty seems not serious for 10v IC refs if you don´t have several of them.
Line regulation is not as bad as the datasheets says in my experience. Last I tested six AD587xQ, two REF102CM and two LT1021CMH with a change of input voltage 15-20-15v the AD587 were best with about 1-3ppm change, the REF102 about 3-5ppm and LT1021 was worst with about 8-10ppm (Note LT1021 had about 5-7ppm/C before compensation the others below 3ppm/C). So datasheets doesn’t say everything. The spec for REF102C is 1ppm/V, LT1021 4ppm/V and AD587 10ppm/V.
Reverse voltage protection is necessary from bitter experience. I mostly use a schottky diode 40v 1A like the 1N5819 which gives about 0.2v voltage drop at 2mA. Sometimes I have added an LP2951 set for 14v to get better line regulation. The LP2951 is cheap (<1USD) and draws little current and have worked well for me.
Having short-circuit protection with an extra buffer like Alex has with an LT1097 for the LT1021 is probably good but I have never used such protection. One thing to remember with buffers is to test with capacitive loads. Not all can handle that. I have once short-circuited a MAX6350 for a couple of minutes and that gave a permanent shift of -30ppm but that is the only time and I have measured references without protection lot of times. Some time I shall test an AD587JQ short-circuited.. some time…
I have never used protection for over voltage on input or output for my own designs and don´t remember I have had problems either. At work I always design in this but am not sure if it really works. Actually surge or burst tests is seldom needed on outputs like these (if you don´t have extremely long cables).
Having EMI protection is very good as you never know if you have any RF-fields nearby. But it is the same problem as with over-voltage protection. It is not easy to design and verify. Having appropriate bypass capacitors and ferrite beads have worked for me. Have done some EMC tests at home just with an HP8657B signal generator sweeping with a small loop close to the output binding posts from 1Mhz to 2GHz reveals that most of my 10v refs still have susceptibility to relatively small RF fields. My SVR boards and also the 2ppm eBay are worse than the once I have better EMI protection on. I have not tested my VREF10-003. If I remember correct the Fluke 732B has a very low spec of 0.18V/m (needs controlled lab environment!). Normal equipment for home use is tested at 3V/m and the equipment I work with is tested at 10V/m or more. You can really have large errors if the RF signal gets rectified. The really nasty problem with EMI is that you can calibrate your 10V ref in one environment and at home you have different RF fields and may be off many ppm without knowing.
Having the reference in a case is absolutely recommended, mostly due to air drafts. I can´t say that having a metal or plastic case seems to make a difference for me. Neither from an EMC or stability point. One reason the metal case is of little use for EMC is that the noise entering through the binding posts are the same for metal and plastic. Good design of the PCB probably is the best.
I have used different banana jacks and bindings posts including silver and gold plated brass or copper. Except for nickel plated once, I have not seen a difference for my 10v refs. Nickel-plated was a disaster giving easily up to several ppm errors.
Almost all of my 10V refs and resistor references have a temperature sensor. As my reference resistors have no power a PT100 or NTC is my choice for them and to have the same I most often use a 10kohm NTC even on the 10v refs even if I use LM35 on some and it is easier to convert to °C compared to NTC´s.
Lars