STM32F7 Thermal Reset

[Bill Finger]

We have had trouble with a STM32F7769BGT6 resetting when heated to around 45°C. The part should be rated for 85°C, as are the rest of the components on our board. We've looked at the power supplies and they don't show any issues. To duplicate the problem, we heat the uC directly with a hot-air gun. Heating other components does not reproduce the issue, but heating the uC immediately causes the reset behavior.

Has anyone seen anything like this before?

(edit) To add some more information, we just performed an experiment, and it appears that bit 30 on one or more of the core CPU registers is switching from a 1 to a 0. Because the register is holding a memory address, the new incorrect address causes a bus fault.

[Ozone]

Might be interesting to see if the observed fault disappears with reduced core clock frequency.

I have not much experience with F7 models, but I never observed noticeable heat generation (high power dissipation) with similar F4 models.

[Bill Finger]

> I never observed noticeable heat generation (high power dissipation) with similar F4 models

Neither have I. This problem is occurring at high ambient temperature levels that the product must be able to operate under.

[Ozone]

I tend to agree.

The internal timing (rise/fall times) tend to deteriotate with higher temperatures.

I hade once measured a opto coupler, which fell apart at 90°C (which was in spec. for that device).

I suppose your failing boards/MCUs are not satisfying the spec.,

I suppose this point (max. clock rate at full temperature range) is a "guaranteed by design" item, and not individually tested in production.

[Bill Finger]

By reducing the system clock rate to 200 MHz, were able to pass the thermal testing requirements. It appears that this part, at least in the configuration we are using it, is not truly rated for the full clock frequency over the full temperature range.

[Chris1]

Interesting / surprising footnote in the data sheet: "216 MHz maximum frequency for 6 suffix version (200 MHz maximum frequency for 7 suffix version)."

Guess you have a 7 suffix device.

[Bill Finger]

Actually, no, I don't. The suffix 7 devices are unavailable in this package.

[Bill Finger · Accepted solution]

In the end, we reduced the clock core frequency to 200 MHz, and the problem disappeared. I recommend using this frequency for any product that must operate over the full temperature range. In fact, since 216 is only 8% larger than 200 MHz, I recommend 200 MHz for all applications.