Voltage Rating on SuperCapacitors

Hi,

This is probably a simple question but a little experience or advice would be great. I am designing a new system using a micro-controller and a few other bits but it turns out to battery back up the RTCC and nothing else is quite tricky and it is probably simpler and cheaper to just use a separate RTCC chip.

With this in mind i am going to use the AB8013 chip which has provision to charge a backup source with automatic switch-over if the main power fails.

I am currently looking at super capacitors for this purpose but i am not sure what voltage i need. All of the super capacitors seem to be rated quite low. The circuit itself is using 3.3V so is a 3.3V Super Capacitor acceptable?

Normally for an electrolytic capacitor i would give lots of margin on the voltage but to do that here i would have to put two of these capacitors in series and i don't have the board space.

I read elsewhere that normally super capacitors can be used at their rated voltage no problem,

Any thoughts??

Thanks,

Super capacitor individual cells are rated 2.5v.
Therefore a very common configuration is two cells in series, for 5 volts. Use such a device.

A question: who makes the AB8013 chip? I could not find its data sheet.

schmitt trigger said:

Super capacitor individual cells are rated 2.5v.
Therefore a very common configuration is two cells in series, for 5 volts. Use such a device.

A question: who makes the AB8013 chip? I could not find its data sheet.

Click to expand...

You see i am very limited for space and i have found a 3.3V rated Super Cap
https://ie.mouser.com/ProductDetail...GAEpiMZZMuDCPMZUZ%2bYlx/EpfZdXAvqhE5Pkm/ul9I=

Data sheet for the chip is here
https://www.mouser.com/ds/2/3/AB08XX-47355.pdf

Looks a lovely chip to be honest

Any further thoughts would be great but i think i will go with this capacitor

That is a ceramic super cap!
This is New technology, it is not the more common aerogel technology.
Yes, go for it.

schmitt trigger said:

That is a ceramic super cap!
This is New technology, it is not the more common aerogel technology.
Yes, go for it.

Click to expand...

Ah very good, I was thinking it was very small and an odd voltage alright,

Thanks for the help

The ceramic "supercap" is quite nice. But even with very low current consumption of the Abracon RTC, it will provide backup only for a few days. That may be too short for many applications.

The Abracon RTC doesn't recharge the capacitor, you need an external low leakage diode.

FvM said:

The ceramic "supercap" is quite nice. But even with very low current consumption of the Abracon RTC, it will provide backup only for a few days. That may be too short for many applications.

The Abracon RTC doesn't recharge the capacitor, you need an external low leakage diode.

Click to expand...

If you refer to the application notes, Section 5.15 you will see it has a trickle charger built in to it,

https://www.abracon.com/Support/AppsManuals/Precisiontiming/AB08XX-Application-Manual.pdf

I only need the clock to back up for a few hours in the event of a power cut so size is no problem,

Thanks,

If you refer to the application notes, Section 5.15 you will see it has a trickle charger built in to it.

Click to expand...

Very good.