Automotive temp MCU

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I am looking at replacing several hardware chips with an MCU.  I
considered this once before but was looking for a lot more in the way of
IO than I am now.  Also, this time the MCU has to operate over the full
automotive temp range of -40 to +125C.  I have looked at several
manufacturers web sites, but they typically don't include temperature
range in the guides.  So I have to pick the dozen or so that are a
likely fit otherwise and then download every data sheet.  

I thought I might ask here for chips that anyone has used before that
would fit my needs.  

-40C to 125C range (of course)
18 or more IOs (after accounting for ISP)
at least two outputs must drive LEDs at 20 mA
very little RAM and Flash size requirements, they just have to be there
the flash has to be writable by the MCU (or data EEPROM will do)
temperature measurement or ADC inputs
small package; TSSOP or QFN or very small QFP (like 48 TQFP)
low price, <$3 in 1k qty
easy to buy in 100's or 1000's

I have found a PIC16F818, but the IO count is very tight.  I expect that
after setting it up for ISP it won't meet my needs.  Microchip is *very*
hard to check for automotive temp since they have literally hundreds of
chips and temperature is not listed anywhere other than in the data
sheet (and is not always noted very clearly there).  Atmel AVR chips
don't seem to come in automotive temp at all AFAICT.  Motorola makes a
few, but none seem to fit all my requirements (mainly pkg and cost
issues).  Cygnal is way too expensive and doesn't seem to be

Any others that I should look at?  I bet there are tons of low cost
automotive 8051s.

Re: Automotive temp MCU
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Something like the P89LPC932 (etc) ~$2.27  ?
comes in HQFN28 package
Abs max spec (bias) is -55'C-125'C
Std data shows Industrial specs, so I'd ask a FAE about Automotive.

Full data for Automotive for smaller uC is not so common, as the
extra test costs have more impact, so you'll find some that spec
MIX/MAX Industrial, and graph/spec typical for wider.

The reality is in actual use, a device will NOT be asked to
run at 123'C for thousands of hours.


Re: Automotive temp MCU
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Thanks for the info.  The P89LPC932/3 seems to be about exactly what I
am looking for other than the temperature.  Motorola seems to be big in
automotive temps, but it is a real PITA to use their web site.  I
finally found a couple of candidates there.  I seem to recall that
Motorola does not make it easy to get a development system, you have to
shell out a few bucks.  

We'll see what Philips can do for me.  I'll contact the local rep on

Re: Automotive temp MCU
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Motorola are very good for automotive temperature parts.  Visit to bypass the non-semi stuff.

I don't think you'll find much for under $3 though.  A reprogrammable
HC05 of HC11 will cost you significantly more than that.

I think a PIC may be your best bet.  They work reliably at 125 ambient
and fit your price requirement.


Re: Automotive temp MCU

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I think you may need to look at a more recent price list (or maybe
just a more recent part).  Newark's single-piece price for a
68HC908QT4 in -40 to +125 temperature grade is US$2.99.  That drops to
$1.97 when you buy 25. I can't give you Digikey's price because they
carry only commercial-grade (-40 to +85) parts.

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The QT4 gives you a much nicer core and more Flash (4k vs. 1k)and RAM
(128 bytes vs. 64 bytes) than a PIC12F675, but the I/O is not quite a
flexible.  Digikey's price for the PIC in the extended temperature
range is $2.30 for 1, $1.48 for 25.  I can't give you Newark's price
because they don't carry the right temperature grade.  And so it


Change is inevitable, progress is not.

Re: Automotive temp MCU
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Thanks for the info Dave, but this chip only comes in 8 pin packages.  I
need at least 20 pins and am more comfortable with 28 (20+ IOs).  The
Motorola site lists the 1k price as about a buck, but then a lot of 8
pin MCUs are a buck.  

MC68HC908JL3  - LQFP48 - <$3  - no dedicated serial IO
MC68HC908JL3E - LQFP48 - <$3.57  - no dedicated serial IO
MC68HC908GZ8  - LQFP32 - $4  - SPI
MC68HC908EY8  - LQFP32 - $(can't find)  - SPI

So there seems to be some Motorola options, but they are no smaller than
the PIC as Motorola does not have the small packages at this time and
all the more cost effective parts (less Flash and RAM) also have too few
IOs.  They don't seem to use any TSSOPs above 16 pins and they don't
have any QFNs listed at all that I can find in the Q1 '04 selection
guide.  So without a smaller package, they would have to have a very low
price to be a better choice than the PIC.

Re: Automotive temp MCU
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I'm baffled by all the postings I've seen on this thread.
In one of them it was said that the application was instru-
mentation for a locomotive, but there's an obsession with
finding the physically smallest MCU possible; given the size
of most railroad locomotives, it's hard to imagine size
being particularly critical.

It was not stated as to whether test instrumentation or
permanent, operational instrumentation was meant, but if
the former, it's hard to imagine a slight difference in
price of an MCU being much of a factor;  if the latter,
given the multi-million dollar price of locomotives, a
dollar or two difference in the price of an MCU is negligible.

Another posting said something about wanting to monitor Vdd.
This would seem to be a matter of trying to measure a voltage
with the voltage being measured, regardless of how one goes
about doing it.  It's also hard to imagine a need to monitor
Vdd (except for operating/fail) in any event.

Re: Automotive temp MCU
On Thu, 29 Jan 2004 08:57:39 PST, the renowned

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Sounds like a batter-powered instrument of some kind, maybe
specialized data logger.

Best regards,
Spehro Pefhany
"it's the network..."                          "The Journey is the reward"             Info for manufacturers:
We've slightly trimmed the long signature. Click to see the full one.
Re: Automotive temp MCU
"Spehro Pefhany
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Yes, many of the apps for this board are remotely located, running off
batteries.  The board shuts down and only has to power the RTC in this
section of the board.  When needed, it wakes up and runs the DSP
application and returns to slumber.  Some customers only need to run a
couple of times a day for a few seconds.  So the power of the sleep
circuit can still be significant if it is too high.

Re: Automotive temp MCU
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This board is for multiple applications.  The locomotive app was one
that illustrates the need for high temperatures.  

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Again, this board is to be sold for multiple apps.  A dollar may not
make a big different in the end cost, but if selling 10,000 units over
the next few years, a buck parts savings will provide an additional
$10,000 in profits.  Certainly it is worth a thorough examination of the
available parts.  

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Since when is Vdd used as a reference for measuring *anything*?  That
was my point.  Some of the chips use Vdd as the refernce for the on chip
ADC.  With most Vdds being 2 or 3% accurate, this seriously degrades the
performance of the ADC.  Most boards these days have multiple power
supplies on board.  This board will have five DCDC converters and will
have two separate 5 volt sections.  

I find that most engineers want to rework the problem that is being
solved.  I have minimized the solution to either one chip or two.  Now I
am just trying to find the best choice to suit that decision.  In any
case, this chip must meet automotive temps.  

I have been told that the Cypress PSOC chips will be available in
automotive temp range shortly.  If I can confirm that, this may be a $2,
one chip solution.  Smallest size (QFN), lowest cost and fewest chips; I
see that as worth a few days of searching.

Re: Automotive temp MCU
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Thanks for the info.  I have looked at the Motorola stuff.  As you say,
they have good parts, but they are not in the price ball park.  I may
revisit them just one more time.  I seem to remember looking at some of
their larger 8 bit parts before and found that their ADCs could not work
with an external reference and don't have an internal one.  It uses the
Vdd level as the ADC reference.  I tried to discuss this with them and
the problems it can create since most Vdd sources are not better than
about +-3% once you add in the tolerance of the set resistors.  But they
seemed to think this was not an issue.  So what is the point of having a
10 or 12 bit converter if it is only accurate to 5 bits?  Heck, I am
trying to measure the Vdd with this - it would always read the same
level!!!  I think the COP parts had the same problem.

Re: Automotive temp MCU
Have you considered putting the computer in an insulated box?

I did this for a couple of test projects and was impressed with how little
foam I needed. Depending on what semi's are in the box a little 'self
heating' might help as well....

just another way of looking at it....


Re: Automotive temp MCU
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I'm not sure what you mean.  I am not worried about the low end.  It is
the high temp end that is the problem.  I think a foam box would be more
of a problem than a cure.  


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I must say that I am a bit dissapointed in Atmel in this search.  They
have a page on their web site that talks about automotive devices, but
little specific content.  I can't imagine they don't make AVRs for the
automotive market.  But maybe they do everything on a custom basis
because of the large volumes.  Still, I can't see not having even one
standard automotive temp product in the AVR line, it is such a nice

Anyone from Atmel care to comment?

Re: Automotive temp MCU
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I think I found a good one at Microchip.  The PIC16F872 comes in
extended temperature rather than "automotive" which explains why I
couldn't find parts in a search.  It also turns out that Microchip will
make extended temp versions of chips and not put it in the data sheet or
in any selection guides.  They really do make it hard to use their
chips.  The price on this one is a bit higher that my target, but not by
much.  It meets all the above criteria except for the package, but they
have a SSOP28 which is not overly large at about 50% larger than a 28
pin QFN.  I can live with that.  I can buy them at Digikey although not
in onesies-twosies.  There minimum on most extended temp parts is what
the maker requires, 260 or so in this case.  

I would still like to have a second choice and I wouldn't mind cutting
the price a bit more (sometimes I can be a real penny pincher).  I
looked at Motorola (nothing below $4 that meets the specs), Atmel
(nothing automotive that I could find), National (nothing to the spec),
Fairchild (only very tiny parts), Analog Devices (MicroConverts are a
bit steep), Dallas (too pricey) and I even looked at Intersil (the old
RCA 1802 which has no memory on chip it seems).  

Did I miss any good candiates?  I am shy of the Asian companies because
they can be very hard to buy from, much less get support.

Re: Automotive temp MCU
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You can probably get better pricing on the part if you check with
Future Electronics /

PIC16F872-I/SS is listed at $2.90 each if you buy them 47 at a time (1
tube).  Somewhat cheaper than Digikey.

And if you just want a few to "play" with, Microchip has a pretty good
sampling policy.  I think you can get up to 3 or 5 parts per 6 month
period free.

Rob Young

Re: Automotive temp MCU
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Thanks for the info.  But I already checked with most of the major
distributors.  I also checked with who can search
multiple vendors.  The inventory at Future does not do me much good
since I will be working with  the -E/SS parts rather than the -I/SS
parts.  Although I would prefer to work with the /ML package that the
872 does not seem to come in.  I might try to use the PIC16F818 in the
-E/ML version as it is about the same, but has fewer IO.  But if I use
the smaller 818 in the /ML package and need the extra IO, I will be
stuck!  We'll see how confident I am in the IO count as the design

I am a bit surprised that no one has been able to point me toward
another maker or two of automotive MCUs.  I guess the pickin's are
pretty slim out there.

Re: Automotive temp MCU

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  This will likely be because the 125'C is mainly under-bonnet - and
that's high volumes / large NRE / narrow customer focus.
  It's also not where a $3 uC will be found....
  For Dash/Boot/Cabin applications, 85'C is fine, and that's where
a much broader cutomer range applies - mostly it's the lower
temp range that is important.

  Do you have numbers on the amb your uC will ACTUALLY be asked to
operate in ?


Re: Automotive temp MCU
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125C or higher if I could do it...

This will be used (among other places) on a locomotive as part of some
test gear.  When in a tunnel the temps can get very high from what I am

Re: Automotive temp MCU

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How long does it spend in the tunnel ? If it is only momentary, some
insulation and/or some massive metal parts may limit the rate of
temperature change.

Also look at the MCU maximum junction temperature and thermal
resistance specifications. You might be able to run the MCU at a clock
frequency well below the nominal clock frequency and since the power
dissipation is usually directly proportional to the clock frequency,
you might be able to run it at a sufficiently low junction

Also adding some large heat sink may help. Assuming maximum Tj of 150
C and a thermal resistance from junction to ambient of 25 C/W, you
could dissipate 1 W, however, if the total thermal resistance can be
reduced to 10 C/W, 2.5 W could be dissipated or alternatively the
junction temperature could be 135 C at 1 W.  A heatsink could be
useful even with many low power devices that you would never consider
using at normal temperatures.

However, a large heatsink may be a problem, if there are large
accelerations or vibrations.

If everything else fails, you might consider using a Peltier cooler,
but remember, that you must have a place for dumping not only the heat
generated by the electronics, but also the heat generated by the
Peltier element (U x I). The efficiency of the Peltier is not very
spectacular, so be prepared to dissipate quite a lot of power.


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