RTC suddenly changes

[kbk1]

Hi

We have a custom board with LPC1788, where we use the RTC, backed up with supercap (appr. 1 week backup time)

We have a small amount of the boards at customers (25), and normally, the RTC works fine.

But one customer has observed that the RTC changes out of nowhere:

After some days where RTC was OK, the DOM (day of month) changed to 00. But the RTC worked fine after this, and after 1 day, it changed to 1, and next days, it also increments the day.

Month, year, hour, minute and seconds was never changed, but incremented as expected.

The issue is never seen on other boards.

What can make this happen?

The voltage on the backup pin is 99,9% OK, but it has not possible to measure it.

Thanks

Kaare

[jeremyzhou]

Hi Kåre Bach Kjeldsen,

Thank you for your interest in NXP Semiconductor products and
for the opportunity to serve you.
It seems a bit weird and it's hard to figure it out according to your above introduction actually.
So I'd like to suggest to mount a definitely work-fine LPC1788 to replace the 'weirded' LPC1788 to validate the hardware of the custom board, please give a try.

Have a great day,
TIC

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[kbk1]

Hi

We deliver the boards to our customer, and he installs at the end-user.

We have only seen the problem at one end-user, out of 15.

And we have never seen it happen during our development process, for the last 2-3 years.

Hopefully, most of the 15 boards is with a "definitely work-fine" LPC1788 :smileyhappy:.

I don't think it makes much sense to change the MCU on that specific board, when we have 14 other boards running?

The firmware logs every event, and shows it on a display, with timestamp.

And here we could see that it suddenly has changed the DOM to 0.

When we make a timestamp, we read the RTC registers directly.

br

Kaare

[jeremyzhou]

Hi Kåre Bach Kjeldsen,

Thanks for your reply.
1) I don't think it makes much sense to change the MCU on that specific board when we have 14 other boards running?
-- To be honest, I've not encountered this similar issue yet before.
So in my opinion, more testing would allow us to figure the cause out, and changing the MCU usually is the first step according to my experience.

Have a great day,
TIC

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