[volt-nuts] LM399 newbie - questions

Andreas Jahn Andreas_-_Jahn at t-online.de
Thu Nov 5 17:39:49 EST 2015


there is a long LM399 thread on EEVBLOG which answers many of your 
Some information for LM399 is also on the LTZ1000 thread.

With best regards


Am 05.11.2015 um 10:30 schrieb Ian Johnston:
> Hi all,
> Am playing around with designs for a precision voltage source and have a
> prototype up & running (may have seen on EEVBlog mailbag video recently).
> It's based on an 18-bit DAC and at the moment I'm using a MAX6350 vref IC
> (plastic package). I chose the 6350 originally for it's low tempco.
> The 6350 is only really good for 16-bit, it's kinda pushing it to be used
> for 18-bit and this becomes apparent by way of thermal drift & thermal
> hysterisis.
> So, I am looking at using the LM399. I have breadboarded it just to get my
> feet wet in regard to it's usage and after a bit of playing around have it
> working pretty good. I'm self-bias'ing it using a chopper op-amp and it's
> pretty stable, totally independant of supply variations, not really effected
> by temperature that much (extremely low tempco resistors used) etc etc.
> I've logged a good bit of data (6.5 digit DMM & BenchVue) and noticed that
> when I first got her up and running there was quite a steep rise on voltage
> on it for a few hours and then it started to level off.
> After a day or two it's much flatter but still on the rise i.e. 40uV
> overnight. Sometimes it will level off a bit then it may start climbing
> again.
> I've ruled out a tempco issue and am starting to think it's an issue with
> having the LM399 on the breadboard......i.e. the mechanical stress is
> continually varying.
> Of course it's probably aging as well, and thats where I have a couple of
> questions:-
> If I go into production with my product (low, low volumes) then can I
> advance the aging process to at least get it down to a reasonable level i.e.
> single digit uV over a few days/weeks.
> Does the aging process have to be done with power applied, or can it be done
> by heat cycling the LM399's.
> If I build a special PCB where I can pre-age say 10off LM399's at the same
> time, what effect will removing from that PCB and then soldering into my
> target PCB's have. The special PCB could have sockets or possibly they would
> be soldered in.
> So far the LM399 is looking good, even on the breadboard, compared to the
> MAX6350 which is in place on the target PCB.
> Thanks in advance,
> Ian.
> [Sent by MDaemon Mail Server at IanJohnston.com]
> _______________________________________________
> volt-nuts mailing list -- volt-nuts at febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts
> and follow the instructions there.

More information about the volt-nuts mailing list