FW: Re: Can I noise hang a ColdFire forever...?

-----Original Message-----
From: Doug Eaton [mailto:[email protected]]
Sent: 07 March 2008 15:54
To: ColdFire
Subject: Re: [ColdFire] Can I noise hang a ColdFire forever...?


Dear Ricardo,

The very high voltages generated when an inductor current is quickly stopped
can easily cause electrical sparks to occur.

These flashovers can cause very high currents (tens of AMPs) to flow,
possibly causing ANY CMOS IC to go into latchup,
and possibly, depending on the course of the current, destruction of any
semiconductor device in the way.

The latchup currrent for any CMOS device will be specifed, and the device
will stop dead if you get it to latchup.
An external watchdog isn't going to get the chip working again. Nothing
short of total power removal will work.
Look at the operation of the thyristor. That's what you get when CMOS
latches up.

If you want to stress your design in this way, and as part of EMC testing
you do expose sensitive electronics to
devices generating lots of volts, use a piezo gas lighter. The sparks that
they generate will stress your design in
a more controllable way than switching off a relay without a snubber diode
or capacitor.

I can accept no responsibility for anything that you destroy using such a
device! Be warned!

If you have the money, you can use a professional EMC high voltage tester to
be more scientific and controlled still.

Remember also, that over voltage stress can damage CMOS structures so that
they fail sometime later,
even though they seem fine during the tests.

Good Luck.

Kind regards, Doug Eaton.

Dear Joshua
...Why doesn't the relay have a freewheeling diode or some other means of
suppression? ...
This diode ausence is not a design specification, just a way to experience
the ColdFire protectios x EMI, besdes superficially evaluate the target if
installed in a not clear enviroment. I mean, exactly because I want to
generate a EMI disturb.
At the begining of this discussion I was very tended to use external
watchdog, but now I´m think that the only way to guarantee  the ColdFire
doesn´t  hang  (considering it has not get damaged) is by using external
watchdog.
I experienced many many 8 bits designs, and I conclude that this machines
reached a very good level of protection against this kind of situation, I
mean, not that they don´t reset, but they don´t hang, including many
Freescale devices...
I got a bit disappointed with it...  I thought this subject was already
"robustly" solved, considering ColdFires are a reasonable year old
devices...but ...lets face it as it ...
Very thanks for your attention Joshua

--------------------------------------------
Doug Eaton
Embedded Products - Development Manager
Email: [email protected]
--------------------------------------------


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