Supercap charging

Discussion in 'The Projects Forum' started by oleoleo2, Apr 4, 2011.

  1. oleoleo2

    Thread Starter Active Member

    Jan 3, 2009

    I need some help with a simple circuit. Hope someone has some experience on the subject.

    I need to make a small circuit with an RTC IC (eg. this The functions is that it has to log the time if the power fails for atleast a couple of days (it's sort of a tamper function/protection).
    The RTC chip seems to be able to do that so I figure it would be smart to use a supercap to feed the IC in "powerfail-mode".

    I have looked at this one:

    It seem to fulfill the needs (regarding case size, operating current/voltage).

    My questions is:

    1. In the datasheet the only voltage and current levels I can find is Maximum operating levels. I assume that is what the cap can deliver when not being charged(?). Then what about breakdown voltage and charge current?

    2. Do I need to design a charging circuit for the cap?

    Hope someone can help!

  2. SgtWookie


    Jul 17, 2007
    Maximum operating current is 10uA. That's charging or discharging. It will take quite a while to charge an 0.2F cap from 0v to 3.3v at a 10uA rate; about 18 hours, 20 minutes.

    Maximum voltage is 3.3v. Don't exceed that and you'll be OK.
  3. oleoleo2

    Thread Starter Active Member

    Jan 3, 2009
    Thanks a lot SgtWookie!
    That certainly straitened the things out :)