I am currently designing an electronic board and i got a question:

Do you know if there is any device in which are integrated an RTC, an EEPROM and a battery? I heard about this type of device (i think it is called Time keeper) but I can't find any.

Thank you


You're probably thinking of the M41T00CAP in the Timekeeper© series from STMicroelectronics. That is/was an RTC with integrated battery, and was housed in a DIP-24 package. Digikey still has them, and ST still indicates them as active, but it may be nearing end of life: those big DIL packages are not much used anymore. They also cost a multiple of what you would pay for a separate RTC and battery.

RTCs with integrated battery offer little advantages over others, especially now that packages are really small, so that you only have to count the size of the battery. I think that's the main reason why you won't see them much anymore.

RTCs will have some RAM instead of EEPROM. RAM is cheaper (you don't need the charge pump to generate the programming voltage), and since the RTC needs permanent power you have non-volatile memory for free. And RAM doesn't have a limited number of erase/write cycles.

A battery like the BR1225 has a capacity of 48 mAh, which will power an average RTC for 10 years continuously.

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  • \$\begingroup\$ Thank you very much for this answer. It was exactly what i was looking for \$\endgroup\$ – damien Oct 4 '12 at 14:45
  • \$\begingroup\$ @stevenvh: What would be called the type/category of the holder part in your picture of the BR1225? Compared to the bulky coin-cell holders I've seen, this seems much more compact! \$\endgroup\$ – boardbite Oct 4 '12 at 15:21
  • \$\begingroup\$ @Inga - it's the tabbed version of the battery. It's not a holder, the tabs are laser-welded to it. A (not so very good) drawing here. \$\endgroup\$ – stevenvh Oct 4 '12 at 15:36

There a few RTC modules out there, here is one option that uses the DS1307 (which has 56 bytes of EEPROM IIRC) and has an onboard battery:

Sparkfun RTC module

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Another one here with 236 bytes of non-volatile memory (battery holder on underside):

enter image description here


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