Automotive temp MCU

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.

-jg

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 Monday.

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....

Jay

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.

:)

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 MCU.

Anyone from Atmel care to comment?

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.

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 snipped-for-privacy@ieee.org

Thanks for the info. But I already checked with most of the major distributors. I also checked with Freetradezone.com 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 progresses.

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.

hi, 125deg used to be the military grade, have things changed while I wasn't looking? Can't you get away with 85deg?

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 ?

-jg

Microchip's sampling is very generous! I've gotten at least 5 different mcu samples. They ship it to you in less than a week, direct from Thailand or something like that.

Have a look at the ST6 series from ST

They may do what you want but the temp range is only -40 to +85. Something like the ST6265 has 21 i/o, 3884 byte user ROM, 128 bytes RAM, 128 bytes EEPROM. 8 i/o can drive

20mA, 8 can be ADC input, any digital i/o can be used for interrupt. Has other "nice" features as well - but it is slow nowadays - 8MHz crystal divided by 12/13 for internal clocks.

Alan

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Mil temp is *-55C* to +125C while automotive (or Microchip calls it "extended") is *-40C* to +125C.

I am building a board that will run at up to 85C, but it will shut itself off at 85C and survive up to 125C. The part that controls the on/off (which also includes a low power mode with multiple wake up options) is simplest if I use a small MCU. If I use other, non-programmable parts, I end up with several devices to replace the MCU. By adding the MCU I also get several other features that otherwise need even more chips.

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 told.

Thanks for the reply, but the temperature is what this question is all about. I can find lots of chips that meet all the other requirements including the tiny QFN package and the low price.

I can also find parts that are automotive temp, but they fail in one of the other requirements. I found one that is only slightly out of my price range and is about twice as large as a 28QFN. So I can use it if I have to. I am just trying to cover all the ground to make sure I have not missed anything.

Too bad Atmel does not have an automotive temp AVRs. I would love to use one of them.

In message , Ralph Malph writes

[snip]

An 85C PIC will easily run at well over 125C - just don't use the internal RC oscillator or watchdog. Are 125C rated parts any different? Don't think so. Try it.

--
Syd

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 temperature.

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.

Paul

Yes, they are different, they are guaranteed to meet spec at 125C if nothing else. I can't come close to testing the parts the way the maker does. Some things like leakage current are important and not worth testing on chips before I make the boards. I have considered building the boards with industrial chips and testing each one, but this can be very expensive.

Thanks for the suggestion anyway.

They can be parked/stuck in a tunnel for hours.

Yes, I am doing that with the LDO. But I prefer to use fully spec'd automotive parts. I have found a number of PICs that can do automotive. Now I am just trying to optimize my choice.

This MCU will be dissipating nearly no power (uWs) when over 85C. So I don't think this is needed.

This part is on the bottom of the board with 0.1" clearance, not much room for a heatsink :)

Far too exotic, but thanks for the suggestions.