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
Am 31.10.2014 um 20:09 schrieb Dan Kemppainen:
Hi All,
I'm working on something that requires a stable voltage reference.
Long term stability isn't needed, but good thermal stability is. In
other words it would be nice to have sub ppm/C temperature, but a few
ppm/month or even per day isn't an issue.
Anyway, it got me thinking about building a reference for fun, with some
of the newer IC's available, but doing so in an ovenized housing.
I know the LM399's and LTZ1000's are out there, but has anyone looked at
any of the newer IC's out there?
For example this one seems to have pretty good ppm/C drift:
http://www.digikey.com/product-detail/en/VRE3025JS/598-1916-ND/2036526
However it's not cheap.
And this one looks pretty good for the sub $10 price.
http://www.digikey.com/product-detail/en/ADR4550BRZ/ADR4550BRZ-ND/3196874
This is the one I was thinking about parking in an oven. It has a
turnover around 70C.
Has anyone played with inexpensive reference chips, and tried to make a
good reference out of them? Any thoughts or comments welcome!
Dan
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