RTC battery run out after several months

[buiphuoc]

Hello NXP,

I am using NXP LPC4078, the RTC module is onchip. To maintain the RTC, I use a CR1620 battery from Panasonic.

In theory, the battery can maintain real time over than 5 years. However, some of my product just run out of battery (measured voltage 0 volt) after around 4 months. Currently, we detected 2 of 500 products that happen the problem.

The circuit design is as below:

with VBAT is connected directly to pin 19 of the LPC4078 100 pin.

I don't known that problem caused by the battery or by hardware. Are there any body met that problem? Please give me any idea to solved it.

Thanks in advance,

[soledad]

Hi,

Please check if you can find any different impedance between a good board and a failed board.

Please measure the current on failed boards and good boards. 

If you change the battery on a failed board, does the problem persist?
I want to isolate the problem and verify that it is not the battery issue.

Have a great day,
Soledad

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[buiphuoc]

Hello Soledad,

Thank you for your reply,

The good board and the failed board are same current, around 1.1 uA. After we detect a failed board, we just change the battery and keep monitoring. but after 5 months ago, the voltage of the battery still hold good.

From that information, may I think that the battery was not charged full? The battery is from Panasonic, a huge company. So that the defect product seem to bee very rare. Our defect rate is 2 pieces per totally 500 pieces.

From your experience, do you think that the battery is not charged full?

Best regards,