Hello.

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 http://pdf1.alldatasheet.com/datasheet-pdf/view/409913/MICROCHIP/MCP79411.html). 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: http://industrial.panasonic.com/www-data/pdf/ABC0000/ABC0000CE19.pdf

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!

/O.

 

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.

 

Thanks a lot SgtWookie!
That certainly straitened the things out

./O