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Does anyone know of an ARM Cortex-M3 microcontroller with both the 3.3V peripheral and 1.8V core voltages supplied by external sources? Everything I have found so far has an internal regulator for the 1.8V CPU core. My problem is that I'm working in a high temperature environment and the internal regulators all have a thermal shutdown circuit to protect the chip which shuts the 1.8V off at 125C. I would like to supply the 1.8V with my own extended thermal protection that will run up to 200C but have not been able to find a microcontroller that will accept one.

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Wow, what are you doing that requires the microcontrollers to be so hot? Can't you just put the mcu outside of the hot area, maybe running wires to some sensors inside? – davr Mar 1 '10 at 18:23

Have you looked into Honeywell's HT83C51. It is a 8051 compatible microcontroller rated to work up to 225C (and derated up to 300C). I believe this chip is designed from the ground up to work in harsh conditions.

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Wow! Thanks Terry. Although I can't make use of an 8051 right now, hopefully someone else will benefit from this post. Another interesting note - it looks like the HT83C51 only comes in a DIP package which may be an issue for some applications. – semaj Mar 3 '10 at 17:57

Even if you do, you will be violating the maximum temperature for the part. It will not necessarily work, even at lower frequencies above its maximum temperature. Remember the "absolute maximum" is for damage, not functioning.

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Thank you. I am aware of this fact. There are no microcontrollers rated to run anywhere near this temperature so we have to do lots of in-house testing. It turns out that many parts run just fine above their rated temperature. – semaj Mar 1 '10 at 18:16
up vote 4 down vote accepted

I found one so far. It looks like the Atmel SAM3S series allows for external regulators to provide power for both the I/O and the CPU core. The down side is that is does not have as much RAM (only 48 k bytes) as most competitors (typically 64 k bytes).

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Yes, the Atmel SAM3S allows you to use external regulators for both 3.3 volt I/O and 1.8 volt core supplies. Be careful with any flash MCU operated above its maximum rated temperature. Higher temp means charge leaks off the flash floating gates faster, reducing the data retention time. You can probably work around if you re-write the flash (and refreshing the gate charges) often. If a typical part has 20 year data retention at 85 degrees C, you may see much shorter retention at 125 degrees C. So be safe and re-write the flash every 6 to 12 months. You will still be on your own. – Atmelfaebrian May 19 '10 at 3:21

Microchip has MCUs that are qualified for 150C operation.

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Thank you Leon. Unfortunately, I have to stay in the ARM family. – semaj Mar 1 '10 at 20:52

Not a Cortex-M3 but LPC2101 ARM7TDMI from NXP requires external 1,8V regulation.

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The maximum operating temperature of the cortex M3 chips I've looked at is 125C - which is right about where you found the thermal shutdown protection.

You'll have to call the manufacturer for use beyond those conditions, but I expect that you won't get the answer you need. You may need to locate the computing elements away from the heat, or use some active cooling solution because there are very few microcontrollers that operate above 125C.

If you want to play with pushing them beyond your limits, though, you're right, you need one that allows an external regulator. I believe both the PIC32 and AVR32 have internal regulators, but they are on accessible external pins and may be bypassed with your own power supply. They aren't ARMs, though, so if that's a core requirement then you may simply need to contact a manufacturer.

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