[volt-nuts] LTZ1000 at higher currents
m1k3k1 at hotmail.com
Sat Oct 22 09:50:37 UTC 2011
This link shows in two of the links that noise is inversely proportional to the square root of the current, and one of them gives a threshold below which the noise increases dramatically.
> From: john at devereux.me.uk
> To: volt-nuts at febo.com
> Date: Fri, 21 Oct 2011 19:33:33 +0100
> Subject: Re: [volt-nuts] LTZ1000 at higher currents
> Hi Frank,
> 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
> > aging.
> > 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.
> > Frank
> John Devereux
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