[volt-nuts] Low Frequency noise on LTZ1000A and tempco ofunheatedLTZ

[Andreas Jahn]

> Well, do not add too many capacitance, otherwise the temp regulation may 
> get stuck,
> heating the element to over 100°C, which may cause drift.

> regards Frank

Hello Frank,

10nF * 10K or 100nF * around 10K will give a time constant of 0.1 .. 1ms. 
The thermal time constant that I have observed is  in the range of  around 
100 ms. So the distance should be enough as long as the output does not 
oscillate.

On the other side the unbuffered output is very critical. By accidently 
loading the output by an unpowered ADC the LTZ-cirquit has drawn about 75mA 
(against 20mA in steady state). Shorting/loading  the output of the 
unbuffered LTZ will set the heater setpoint temperature to a very large 
value. I observed that after this treatment the output was shifted by -11uV 
(-1.5 ppm). The shifted value lasted as long as I did several power-cycles 
with off-time > 2min to cool down the reference.
After 3 or 4 powercycles the old value was restored. So there seems to be 
some thermal hysteresis for large temperature excursions. Unfortunately the 
hysteresis is reached even by connecting of a 1uF capacitor at the output of 
the reference.

Do you have a buffering cirquit on your devices? Im looking for a cirquit 
which does not add to thermal drift and noise. And is not sensitive to 
EMC-noise of course.

with best regards

Andreas