[volt-nuts] LTZ1000 at higher currents
john at devereux.me.uk
Fri Oct 21 18:33:33 UTC 2011
That is an interesting idea and would explain why 5mA is used. There is
an "electromigration" effect that people blame for long term damage
caused by high current density I think,
Taken to its logical conclusion, one could turn on a low-current,
high-noise, low-drift reference once an hour and use it to adjust a
lower-noise, higher drift type. Which could be another LTZ1000 run at
higher current! :)
But.... I don't think the datasheet does give an actual upper limit,
unless I missed it. Just two or three example current values.
The newer(?) LTZ1000A would have a significant temperature rise caused
by the extra current (~15C per extra 5mA) so I can see why 5mA would be
the practical maximum for this part.
Perhaps I should ask them.
The LM399 is another buried zener, the ancestor of the LTZ1000 as I
understand it. It's datasheet does state a 0.5-10mA operating range and
20mA absolute maximum.
Frank Stellmach <frank.stellmach at freenet.de> writes:
> Hi John,
> as far as I remember, higher Zener currents alone (i.e. excluding
> temperature rise effects) let the pn structure age / drift faster
> compared to operation at lower currents.
> This might probably be an exponential effect, so I would not increase
> the Zener beyond the given limit of 5mA at all.
> Remember, a Zener pn junction is operated in reverse mode, and charge
> is highly accelerated inside the silicon bulk material by the Zener
> potential. Higher currents will therefore interact stronger with the
> silicon crystal structure, than lower ones, that means it will create
> more permament defects on the long run, which gives rise to stronger
> Also, this is not a discrete Zener component, but a very delicate
> sub-surface structure, optimized for lowest drift, but presumably not
> for high currents. 10, 20 or even 30mA will for sure damage the Zener.
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