RTC consideration when using a supercap

[bryanh]

First time using a double layer supercap in place of a coin cell backup battery on a  PCF85363A  RTC. I did not see any design notes in the datasheet or in any separate documents. Are there any special consideration when substituting the battery with the cap? 

The PCF85363A does not appear to have an internal charger. A resistor divider and steering diodes can be used to keep it charged and allow discharge only into the RTC. Is anything else needed?

[bryanh · Accepted solution]

Excellent, this is what I was looking for. https://www.nxp.com/docs/en/user-guide/UM10301.pdf

This user manual provides a detailed comparison of different back up methods and lists the pros and cons of each.

Thank you.

[guoweisun]

Please down load UM10301 and read from  page 30--13. Backup power supply