[volt-nuts] LTZ1000 VS LM399
frank.stellmach at freenet.de
Wed Dec 10 17:54:44 EST 2014
obviously, you also have missed these long and exhausting discussions on
EEVBLOG about those two references:
The difference between both is much more distinct:
The LM399 is about 1-2 orders of magnitude less stable than the LTZ1000
and appropriately selected external components.
The LM399 is good for stabilities of about 20ppm/yr. and <1ppm/K T.C.,
i.e. 6 1/2 digits class DMMs.
The LTZ1000 plays in totally different league of the 8 1/2 digit DMMs,
calibrators and voltage standards, i.e. < 1ppm/yr. and < 0.02 ppm/K can
be achieved on intelligently selected components.
The LM399 is fixed on 95°C oven temperaturer, including the buried Zener
and all oven temperature and reference determining resistors.
The LTZ1000 on the other hand can be operated at 45°C, and the oven and
reference determining resistors can be chosen for optimum performance,
which is not true for the resistors-in-silicon of the LM399.
These differences explain the ultra stability of the LTZ1000.
Therefore, you may average as many LM399 as you like, you will hardly
(never) achieve the ultra performance of a single LTZ1000.
If the averaging follows a 1/sqrt(N) law, then more than 400EA LM399
would have a similar stability as the LTZ reference.
Therefore, solely the needed stability determines, which reference has
to be used.
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