How to avoid the mcu failure when power on

[PeterTsai]

I desigen a clock display with external crystal 32.768KHz. I have ran into to  power-on failure  by chance, (probably 5%)

I found out the reason of failure that the crystal don't start to oscillate. I try to start COP function but it still fail.

Please someone could give me some advise. How to avoid the mcu failure when power on?

[bigmac]

Hello Peter,

Do you have LVD reset enabled?  With low frequency crystals in particular, it is very important that this be enabled.  Otherwise it is possible that the potentially long start up time of the crystal may exceed the normal startup time provided within the MCU.

Regards,

Mac

[peg]

Hello Peter,

I have had many S08's that have had the crystal fail to oscilate, but not seen this cause any damage. I had a bad batch of crystals where a very high percentage failed to start properly. Some made it into the field and were left for hours at a time in this condition. Just the crystal was replaced and the devices are still functioning months later.

The only thing I can think is that if the device does not start and pins don't assume the correct levels then connected devices could do the wrong thing and cause problems on other pins causing device failure.