Off Topic: 3.3V Lithium cell on a DS1307 charging

hillcraft · Posted: Sat Oct 08, 2005 11:37 am

I am in the process of redesigning my PLC board and I hope that one of you guys can help me.

Ok, I have the following circuit. A 18F4580 running a variety of IO including a DS1307 RTC. The RTC has a 3.3V backup battery.

Is there a way to charge this cell when the circuit is operational. It would be good to extend the life of this cell as far as possible given that the PLC's are installed in all sorts of strange places.

VanHauser · Joined: 03 Oct 2005 Posts: 88 Location: Ploiesti, Romania

Here's what's written in the DS1307 datasheet: "A lithium battery with 48mAhr or greater will back up the DS1307 for more than 10 years in the absence of power". Think how much will it run with a common CR2032 3V battery with 230 mAhr. If you want only to keep the RTC running when power fails, there's no point in adding charging circuitry.

hillcraft · Posted: Sat Oct 08, 2005 1:36 pm

Yes I think that charging the Lithium cell is really a waste of time.

Thanks