PCF2131 clock running too slow

[kaifalkenberg]

Hi,

I'm having some trouble getting a PCF2131 to run smoothly. The clock is running way too slow. I'm losing several hours a day.

I have followed the manual, in particular chapter 7.3.2 (OTP refresh). The temperature measurement period (see chapter 7.3.1.1) is set to 4min. Besides that I'm using direct switch mode and I can confirm that the clock is still running when switching to VBat.

I also checked the CLKOUT frequency and it looks very stable (tested at 1024Hz).

Any hints on how to debug this any further?

Another thing that came up: I need to add quite long wait cycles (100ms) in between the steps to set the time and date. I have found that hint in another forum thread here in the NXP community, but I cannot find anything in that regard in the datasheet. Any comments on that?

Thanks a lot

[diazmarin09]

Hello kaifalkenberg,

I hope all is great with you. Thank you for using the NXP communities.

How many boards have you tested and failed?

Could you please share your device configuration (schematic) a further analysis?

Regards,

David

[kaifalkenberg]

So far I have only tested one board.

[kaifalkenberg]

Hi David,

thank you for your quick reply. Here is the schematic:

Kind regards
Kai

[diazmarin09]

Hello kaifalkenberg,

Thank you for using the NXP community.

Have you considered using the Aging_offset register to correct the crystal aging effects?

The accuracy of the frequency of a quartz crystal depends on its aging. The aging offset adds an adjustment, positive or negative, in the temperature compensation circuit which allows correcting the aging effect.

The aging offset bits allow a frequency correction of typically 2 ppm per AO[3:0] value, from -14 ppm to +16 ppm.

Please review the chapter 7.4 from datasheet for further information.

Regards,

David

[kaifalkenberg]

Hi David,

thank you for your input. I don't think the AO will be sufficient in my case. +16ppm won't fix the issue. I will wait for a second board to be ready and see if I can reproduce the behaviour.

[diazmarin09]

Hello kaifalkenberg,

Please let me know as soon as you get your new board. I hope this issue is related with a defective part.

Regards,

David