I am experiencing failures of the LSE oscillator on STM32F427VIT6 during thermal cycling.

[BRieh.1]

I have an ESC ECS-.327-CDX-1082 32.768KHz crystal on the LSE of an STM32F427.

I have read and followed AN2867.

All of the boards produced so far have had the oscillator come up initially.

All of the boards subjected to thermal cycling (-20°C to +70°C) have failed. (two)

In each case, the voltage on the pins (GPIO PC14 & PC15) measures 0 volts.

I expect somewhere about 0.3V.

I just replaced the MCU on one of the boards and now the oscillator works again.

Any thoughts?

[BRieh.1]

The solution is to do a backup domain reset. There appears to be a finite amount of time between the backup domain reset and the re-enabling of the LSE oscillator. We can now sucessfully recover from this event. Thanks to all of you who have contributed.

[BRieh.1]

Also, the voltage provided by the supercap never dropped below 2.1 volts.

[waclawek.jan]

Thanks for coming back with the solution.

> There appears to be a finite amount of time between the backup domain reset and the re-enabling of the LSE oscillator.

Can you please be a little bit more specific, i.e. how much?

Thanks,

JW

PS. Please select your post as Best so that the thread is marked as solved.

[BRieh.1]

Sorry for the delay.

It looks as if it takes 2-10msec after the backup domain reset before the LSE is stable.

[AScha.3]

LSE startup can be long... (from F407 data.)