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'[PICLIST] [EE] MTBF numbers? [ot?]'
2001\11\05@163842 by Dave King

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Does anyone know what the mtbf rating is for any of the pics?
I've rummaged around the Microchip site but couldn't find a
mtbf number.

I've have a sub-board where the component cost is within pennies
of using a couple of ic's or a single pic. The entire board has to
be rated with a mtbf for certification purposes. I can do this
 with a couple of logic ic's and a transistor. I can also do this
with a single pic, a diode, and a transistor. The transistor in each
case is so under driven its not even on the charts aka bullet proof.
The problems are simply which has highest mtbf rate and which would
consume less man hours to produce.  The logic ic's do the basic job
, can be ordered in mil ratings and will have some flexibility. The
pic on the other hand will take programing, the software needs to be
certified/reviewed, but it has infinitely more flexibility in comparison.

I'm curious to see which way everyone would go with this. The main
criteria are reliability and production cost. And each way has its merits.

Dave



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  /_( \__/ )_\
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2001\11\05@193600 by Gerhard Fiedler

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At 13:37 11/05/2001 -0800, Dave King wrote:
>Does anyone know what the mtbf rating is for any of the pics?
>I've rummaged around the Microchip site but couldn't find a
>mtbf number.
>
>[...]
>I'm curious to see which way everyone would go with this. The main
>criteria are reliability and production cost. And each way has its merits.

Interesting question -- unluckily I don't have a clue about mtbf numbers
for PICs. My guess would be though that the discrete logic is way more
reliable. It also seems that production cost is not higher -- leaving the
lower flexibility as sole disadvantage. If your main criteria are
reliability and production cost, I'd probably go with discrete logic.

ge

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2001\11\05@234546 by Dale Botkin

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Oh, you all can't be serious!  It took me all of 60 seconds to find this
on Microchip's site:

http://www.microchip.com/1010/overview/qualreli/relidata/index.htm

Would nothing there be helpful?

Dale
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On Mon, 5 Nov 2001, Gerhard Fiedler wrote:

{Quote hidden}

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2001\11\06@013335 by Dave King

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At 10:43 PM 11/5/01 -0600, you wrote:
>Oh, you all can't be serious!  It took me all of 60 seconds to find this
>on Microchip's site:
>
>http://www.microchip.com/1010/overview/qualreli/relidata/index.htm
>
>Would nothing there be helpful?

Now read through all of that and pull out just one mtbf number...

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2001\11\06@071855 by Bob Ammerman
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I am not an expert on these things, but I believe that all the numbers that
mChip thrwos about in this data are the raw materials from which one can
compute an MTBF, if one knows the appropriate incantation.

{Original Message removed}

2001\11\06@095212 by David VanHorn

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At 07:08 AM 11/6/01 -0800, Bob Ammerman wrote:
>I am not an expert on these things, but I believe that all the numbers that
>mChip thrwos about in this data are the raw materials from which one can
>compute an MTBF, if one knows the appropriate incantation.

Anyone notice that the only acceptable MTBF calculation is:

MTBFours >= MTBFcompetitor_published

If the number that you get after a bunch of research dosen't meet this,
then they tell you it's "unacceptable", even if you calculate the other
guy's and it differs significantly from what they publish.
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2001\11\07@140702 by Peter L. Peres

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> I am not an expert on these things, but I believe that all the numbers
> that mChip thrwos about in this data are the raw materials from which
> one can compute an MTBF, if one knows the appropriate incantation.

MTBF computation requires some sort of failure mode prediction or
analysis. If you accept a hardware that is perfectly working then you can
predict a software glitch by using the S/N in the circuit and the
respective logic levels and their margins. Then you can come up with a
number of seconds required for a 50% probability that a logic state will
be misread and cause a glitch, for each pin. The total will refer to all
the pins. So having a very low number of IOs and redundant IOs helps. As
Alan Pearce said, it is related to the number of joints...

With a computer, that can try to re-read inputs and use redundant outputs
this computation becomes very complex. However normal logic circuits stop
here and computers can be more reliable that normal logic because of it
(computers can try harder). Chip internal logic is considered very
reliable (unless it is made or designed by certain manufacturers <g>).

I think that no manufacturer who has the disclaimer about his products not
being usable for 'life support' and 'critical' applications will ever give
a MTBF figure without the lawyers smothering it instantly.

Peter

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