[volt-nuts] Low-cost voltage reference questions

[Andreas Jahn]

Hello,

MAX6350MJA is unobtanium today
All you can get on the market in small quantities are fakes.
The plastic parts that I have drift all around 10ppm/year (30 ppm in 3 
years)
Further at least some of the MAX6350/6250A parts have some kind of 
"popcorn noise"

REF102CM is also no longer produced
The plastic parts suffer from humidity with several ppm drift.

AD588KQ should behave similar to the other AD58* devices.
But I do not consider this as "low cost".

The LTC6655 is a bandgap -> from principle less stable.
I have measured a large thermal hysteresis (6 ppm) for a +/-15 deg C 
temperature excursion around room temp.
with a LTC6655AILS8-5.
In practical use the 1/f noise is not lesser than on a AD586.
(measured 2.7uVpp)

The long term drift spec in the datasheets are only "typical values" for 
the first 1000 hours.
So have nothing in common with a 1year spec.
Also the tempco values are usually for the whole temperature range.
On many reference types (not all) the tempco at the range limits increases.
(that explains the MAX spec for the military temperature range)
On some references the near 25 deg C temperature gradient is much lesser.
For the AD586LQ  I have measured 23 out of 29 samples better than 1ppm/K 
at 25 deg C.

with best regards

Andreas

Am 25.11.2015 um 12:17 schrieb Charles Steinmetz:
> Andreas wrote:
>
>> Hello Lars,  or course you are right: the AD587 (10V) and AD586 (5V) 
>> are the best (unheated) chips with hermetically package today.
>
> I'm curious why you think the AD587/586 are better than other 
> hermetically packaged references with better drift and noise 
> specifications -- in particular,
>
> MAX6350MJA
> AD588KQ
> LTC6655CHLS8
> LTC6655BHLS8
> REF102CM
>
> (see attached table).  (Note that the hermetic version of the MAX6350 
> has a 2.5ppm/C drift spec, not 1ppm/C as listed in the table for a 
> different package.)
>
> The 587 has a better long-term drift spec than the 6360 and the 6655 
> (but note that the 587 is 3x worse than the REF102 in this regard).  
> To my mind, the better tempco and noise of the 6350 and 6655 outweigh 
> the better long-term drift of the 587 in an overall ranking.
>
> Best regards,
>
> Charles
>
>
>
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