Hi,
 
	Thanks a lot for all the answers. They really helped for me to clean
up some aspects.. I will try to make a small "topics" view that may help
others in the future. If I say something that sounds wrong please tell me.
 
- No one, specially me, seemed comfortable with a power supply that could
vary 2 volts during "cranking" even if that does not violate the specs on
the microcontrollers. So I need to regulate the voltage better.
 
- The car electrical system is a real mess !! The battery does go down to 8
or even 7 volts on diesel engines and still turns the car on ! Spikes of
over 60 volts happen a lot, specially on old vehicles. Negative spikes also
as there are many inductive loads and some of them might be missing the
flybak diode.
 
- Old trucks with diesel engines work for months with the batteries at
"marginal" state ! At least here in Brazil. We have LOT's of old trucks.
 
- My main device does not have to work with a bad battery and may reset
freely as long as it does it gracefully. This one is made to prove to the
client that the problem is in the trucks battery or electrical system and
not on the main device. That is the reason why I have to work "out of the
automotive specifications". 
 
- Making something work at such a huge input voltage range ( 5 to 32 with 60
volts spikes ) is not a trivial problem when budget and components options
are limited.
 
- My final ( I hope ) option is to use a dual stage shunt supply with a
zener on the first stage and a TL431 on the second stage. It takes more
space than the Micrel regulator but is probaly as good as and cheaper. I was
not able to source the Micrel part easily here in Brazil. This will work
quite well because my circuit will eat less then 5 ma. 
 
	I already redesigned the board and should test it by the end of the
week. I will let all know the results.
 
Best regards and thanks again,
Alexandre Guimaraes



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