PCA8565 TS RTC issue:

[srinath18]

Getting time...
Read time: 16:10:36
23-22-2023
Time in seconds 58236
Getting time...
Read time: 16:10:37
23-22-2023
Time in seconds 58237
Getting time...
Read time: 16:10:38
23-22-2023
Time in seconds 58238
Getting time...
Read time: 16:10:39
23-22-2023
Time in seconds 58239
Getting time...
Read time: 56:10:40
63-42-2023
Time in seconds 202240
Getting time...
Read time: 56:10:41
63-42-2023
Time in seconds 202241
Getting time...
Read time: 56:10:42
63-42-2023
Time in seconds 202242
Getting time...
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63-42-2023
Time in seconds 202243
Getting time...
Read time: 56:10:44
63-42-2023
Time in seconds 202244
Getting time...
Read time: 56:10:45
63-42-2023
Time in seconds 202245
Getting time...
Read time: 56:10:46
63-42-2023
Time in seconds 202246
Getting time...
Read time: 56:10:47
63-42-2023
Time in seconds 202247
Getting time...
Read time: 56:10:48
63-42-2023
Time in seconds 202248
Getting time...
Read time: 56:10:49
63-42-2023
Time in seconds 202249
Getting time...
Read time: 56:10:50
63-42-2023
Time in seconds 202250
Getting time...
Read time: 56:10:51
63-42-2023
Time in seconds 202251
Getting time...
Read time: 56:10:52
63-42-2023
Time in seconds 202252
Getting time...
Read time: 56:10:53
63-42-2023
Time in seconds 202253
Getting time...
Read time: 56:10:54
63-42-2023
Time in seconds 202254
Getting time...
Read time: 56:10:55
63-42-2023
Time in seconds 202255
Getting time...
Read time: 56:10:56
63-42-2023
Time in seconds 202256
Getting time...
Read time: 56:10:57
63-42-2023
Time in seconds 202257
Getting time...
Read time: 56:10:58
63-42-2023
Time in seconds 202258
Getting time...
Read time: 56:10:59
63-42-2023
Time in seconds 202259
Getting time...
Read time: 16:11:00
23-02-2023


this is how I'm getting time stamps, proper for first 39 secs, scrap for last 20 secs and proper again

[diazmarin09]

Hello srinath18,

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

Could you please share further information about your device configuration? Could you please share your schematic for example?

Regards,

David

[srinath18]

Hi David,

This RTC sits on a small breakout board, OSC1 and OSC2 pins have a crystal of 32.78 kHz frequency, 10 pF load capacitances, interrrupt and clockout open and the scl and sda lines are pulled up to 3.3V and is interfaced to a STM32.

Hope this is okay to explain why Im having the problem.

[diazmarin09]

Hello srinath18,

I am pleased to contact you again.

1. In this case, I would like to review our oscillator.

The simplest way to check for oscillation is to use the CLKOUT. If the design does not include a pull-up resistor to the CLKOUT, then add one temporarily. Applying a scope probe to the CLKOUT should reveal a block signal with a frequency that depends on the settings in the control registers. Don’t forget to first enable CLKOUT. Could you please share the oscilloscope trace of the CLKOUT pin?

2. Your schematic would be very useful for further analysis.

3. Is your design close to an EMC source?

Regards,

David

[srinath18]

Hi David,

Thanks for the reply, I've shared the schematic of the breakout board where RTC goes on. And, no the design on the bigger board is not near an EMC source. Will share the oscilloscope trace meanwhile.

[srinath18]

Hi David, 

Adding the clokout oscilloscope trace here. Used a 4.7 K resistor to pull clkout temporarily, frequency is proper.

[diazmarin09]

Hello srinath18,

I do appreciate your contribution.

In this case, I would like to add some comments:

1. Have you considered adding a decoupling capacitor between VCC and GND to eliminate possible noise from the power source? I would recommend to use a 100 nF – 470 nF decoupling capacitor close to the RTC with short tracks to VCC and GND.
2.  Could you clarify if the CLKOUT signal is stable at the time when the error occurs?

Regards,

David