Trouble with DS1307 battery backup

[SUNFLOWER]

Very interesting. I did not know about DS1370 battery voltage sensitivity. I used long-life CR 1620 for 10 year clock service and never checked battery voltages with a meter. Something to consider in the future.

[Jerson]

I've seen this problem before. The resolution is in the data sheet section regarding Vbat. This is what it says

From http://datasheets.maximintegrated.com/en/ds/DS1307.pdf page 6

Backup Supply Input for Any Standard 3V Lithium Cell or Other Energy Source. Battery voltage must be held between the minimum and maximum limits for proper operation.
Diodes in series between the battery and the VBAT pin may prevent proper operation. If a backup supply is not required, VBAT must be grounded. The nominal power-fail trip point (VPF) voltage at which access to the RTC and user RAM is denied is set by the internal circuitry as 1.25 x VBAT nominal. A lithium battery with 48mAh or greater will back up the DS1307 for more than 10 years in the absence of power at +25°C

Hope that helps

[Amoque]

Yes, I read the warning and it eventually came back to me as a possibility - it just took too long for me to question that a brand new, off the shelf part would be the problem. FAR more often it is some errant wire or lack of understanding... in my case anyway.

If I've learned anything it is that those weird intermittent problems that come and go are most often related to power supply. Wires don't move and semiconductors don't magically heal - only to fail again - in a random pattern. Well, here's to posterity and "Good Luck" to the next guy.


Cheers,