[volt-nuts] Motorola buried zener

Bruce Griffiths bruce.griffiths at xtra.co.nz
Sun Sep 13 03:12:11 UTC 2009

Mike S wrote:
> At 10:06 PM 9/12/2009, Bruce Griffiths wrote...
>> The reference amplifier(U2) on A4 reference board circuit in the 732A
>> appears to be compatible with one of the Motorola 6.8V reference
>> amplifiers such as the MCA1914N, MCA1924N or MCA1934N.
>> The only difference between these is the specified operating temperature
>> range.
>> If the oven temperature is around 50C then a selected MCA19124N is
>> likely.
>> They had a maximum voltage change (Iz = 5mA) of 5mV over the 0-75C
>> operating temperature range.
>> Reference voltage was 6.8V with a 10% tolerance.
> That sounds right. That's about 10 ppm/C tempco. Any idea what
> Motorola's spec was for long term drift? 732As had a mean drift rate
> of ~0.5 PPM/yr., according to Fluke (about 4x better than the LTZ1000
> spec!), and a tight deviation, both much better than the newer 732Bs .
> BTW, these types were used by Fluke at least through the early '90's,
> in the early 732Bs, so I don't know that calling them "ancient" is fair.
They vanished from the databooks some time ago, probably in the early 90s.
As far as I can tell there were 2 versions, the original in a hermetic
metal cylindrical outer package (in 1967 zener diode hand book) and
another version with a rectangular plastic over-molded outer package (in
1974 Motorola databook).

Neither datasheet has long term drift specs.
I cant find A181 the only application note I know about on reference

The only Motorola long term stability data I've seen is for the MZ600
and MZ800 series reference diodes.
The best of these had a stability of 30uV/1000 hours (for the MZ605-
6.2V reference).
The measured instability may be degraded significantly by the
measurement setup used (oil baths standard cells etc).

I would suspect that selected Motorola reference amplifiers had similar


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