[volt-nuts] LTZ1000 reference appnote question

Chuck Harris cfharris at erols.com
Thu Nov 8 19:06:15 UTC 2012

Hi Fabio,

I think that startup problem could occur if the opamp's
input offset current happened to be such that the - input
was above the + input.  The 30K resistor, by virtue of
its positive feedback, would enforce that condition,
locking the circuit at near zero output.  The diode, at
least, prevents that extra positive feedback from
contributing to the problem.

I don't think the diode will have much effect most
of the time.

-Chuck Harris

Fabio Eboli wrote:
> Hello Chuck, I understand that for dual supply, but is
> this valid also for single supply like that one?
> I was thinking that the lowest voltage in the circuit,
> at least after powerup transient, will be ground
> potential that is also negative rail's potential.
> I agree that, without the output diode, if the out
> is for some reason externally tied few mV below ground
> there is really no hope to start the reference.
> Fabio.

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