[time-nuts] Simulation

[Javier Herrero]

Hello,

I've read at least two similar stories in "Troubleshooting Analog 
Circuits" by Bob Pease.

One is that it seems that some time ago, National Semiconductor started 
shipping LF411s marked as LF351s as an "improvement"... and as Bob says, 
most of the customers probably were happy with that (I think that most 
of them probably never noticed the change), but the gain on the trim 
circuit was reversed (in the LF351, if you turn the trim pot in one way, 
Vos increases - in the LF411, turning it in the same way makes Vos to 
decrease), and this probably would have made some people not so happy 
with the improvement :)

Another story is about 2N3771 transistor, initially a single-diffussed 
part, but later an epitaxial base part - with a lot more gain bandwidth 
product. But since the 'new' 2N3771 meets and exceeds original 2N3771 
specs, the same part number was used - but the part is quite different 
(and published specs continues being the JEDEC ones). So you can imagine 
that in some applications it would be quite a lot of difference if you 
breadboard with the older, and during the manufacturing phase you 
(probably without knowing it) switch to the new part.

I suffered some time ago a change in a small DSP from Freescale. It is a 
3.3V part with 5V tolerant I/O, and I assumed (not sure if this was in 
the datasheet or not) that reset pin was also 5V tolerant. Prototypes 
worked, and production worked, but after 2-3 years of production, and 
from some DSP production date code, we experienced a problem with the 
part reset - the part did no longer liked the 5V level at the reset pin. 
I asked Freescale about any change, but never got any response.

I periodically receive PCNs (product change notifications) from EBV 
Elektronik, which is a quite big european semiconductor distributor, 
whenever some product that I'm purchasing or have purchased in the past 
suffers some manufacturing change (manufacturing moved to other plant, 
process change, case materials change, etc...), like for example this 
one: 
http://www.ebv.com/fileadmin/templates/scripts/pcn/data/200907002f__1248209503.pdf 
But I suppose that not all manufacturers are so kind to let the 
customers know in advance these kind of things :)

Best regards,

Javier


El 14/08/2010 14:30, Bob Camp escribió:
>
> Hi
>
> Simply a few stories I thought I would share.
>
> Simulate design. Use manufacturer's published models. Build design. Note differences. Call manufacturer. Answer - switched die three years ago, Ft is now " much better " ( now 3x old parts ).
>
> Odd they never mentioned that to people who work for the same company.
>
> Simulate design, Build design, verify design, ship it for a few years. Odd things start to happen. Look at some parts. Package looks different. Ask around..... Line got moved to other side of big ocean. Process got " tweaked" beta is now 4x what it was.
>
> Again all inside the same company. Both cases were excused by industry standard specs that had no upper limit.
>
> We had whole departments devoted to tracking this sort of stuff. It still happened on a regular basis. 30 years later the specs on the devices and their published models are still the " old version " ones.
>
> Bob
>
>
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Javier Herrero                            EMAIL: jherrero at hvsistemas.com
HV Sistemas S.L.                          PHONE:         +34 949 336 806
Los Charcones, 17                         FAX:           +34 949 336 792
19170 El Casar - Guadalajara - Spain      WEB: http://www.hvsistemas.com