[volt-nuts] Voltage Reference.

[Dan Kemppainen]

Rob and Andreas,

Thanks for the feedback. You both brought up plastic housings as a
concern. It was an issue in the back of my mind also.


Rob,

I did get your email directly, but not the one on the list. Weird.


Andreas,

I always see references to the LM399 and LTZ1000. I was just going
through the mental exercise of 'what if'. Of course, it appears you have
gone through the real exercise of 'what if'!

So, it appears that the LTZ1000 is still the best there is. I see they
are available the linear web site, so may pick one up to play with this
winter.


Thanks for the input!

Dan




> 
> Hello Dan,
> 
> If you look for sub-ppm then also noise or hysteresis might be a issue.
> Nearly all good references have around 0.6ppm low frequency noise with 
> respect to output voltage.
> (giving 3uVpp for 5V).
> 
> I have tested 2 VRE3050A for noise and one for TC.
> In the range of 16-40 deg C average tempco was low (about 8 ppm over 
> 16-40 deg)
> (nearly zero around 28 deg C)
> but hysteresis at 25 deg was 4 ppm and 0.1-10 Hz noise around 9uVpp.
> The second VRE I have only tested for noise which gave also around 9 uVpp.
> I do not know if both devices are "mondays" devices since I bought them 
> at a time shortly after Thaler was sold to APEX.
> And current consumption was far below the value of the datasheet.
> But for me I decided that they are no good value for money for my needs.
> 
> For the same money you get 5 AD586LQ with <3uVpp noise and nearly no 
> hysteresis in the above temperature range.
> Ok perhaps you have to select them for tempco. In my case tempco is 
> compensated by a microcontroller with a (NTC) temperature sensor.
> 
> The ADR4550 suffers like nearly all plastic housings from large 
> hysteresis and perhaps from humidity sensitivity.
> I measured a nearly linear average tempco of -2ppm/K on one sample. 
> Hysteresis around 16ppm at 25 deg C.
> Noise was around 3uVpp like good buried zener devices.
> 
> The LM399 that I have tested are far better in T.C. than the 1ppm/K that 
> are stated in the datasheet.
> At least this is true around room temperature (10-40 deg C).
> Only noise is rather different from device to device.
> Some around the 0.6 ppm others are a factor of 2 or so larger in noise.
> So perhaps you will have to select for noise.
> 
> Some Info of other features of LM399 (tilting drift, termal isolation) 
> can be found here:
> http://www.eevblog.com/forum/projects/lm399-based-10-v-reference/
> 
> If you need low T.C. and low noise there is nearly no way not to use the 
> LTZ1000
> http://www.eevblog.com/forum/projects/ultra-precision-reference-ltz1000/
> 
> With best regards
> 
> Andreas
>