Using a supercapacitor with the PCF2129 How to determine if the data is useful?

[dominusdrr]

Hi.

When using a supercapacitor instead of a battery, the flag called BLF is in 1 logical, which is used to determine if the battery is no longer useful but in this case I think it may not help.

Something that I have determined is that the time and date information of the RTC is out of range when the capacitor has been discharged and its voltage has not been sufficient to retrieve the information.

For example, minutes have a value greater than 0x59.

I think that checking all time and date registers may be an option to determine that the RTC needs to be matched but at the same time I think it is a cumbersome solution.

Is there a way to check faster or more effectively that time and date data are corrupted?

Any ideas or comments are welcome.

[dominusdrr]

The most optimal solution is to verify that the time and date values are logical, if not, it should be assumed that the RTC must be matched.

[guoweisun]

Hi

You can also use BLF flag for monitor voltage level of super capacitor.

The flag BLF remains logic 1 until the battery is replaced. BLF cannot be cleared by
command. It is automatically cleared by the battery low detection circuit when the
battery is replaced or when the voltage rises again above the threshold value. This
could happen if a super capacitor is used as a backup source and the main power is
applied again.

[dominusdrr]

Hi. Thanks for write.

That is, when you work with a battery, when you remove it and place a new one, that flag is cleaned.

But the capacitor cannot be removed, if it is the first time the device works or if the capacitor has been discharged to a very low voltage. When the RTC is energized, the capacitor takes a while to reach an optimum voltage level and therefore the RTC "thinks" that there is a discharged battery and the BF flag is set to 1 and stays that way forever, unless you can remove the capacitor fully charged and put it back in its place.

[guoweisun]

If possible,you can insert jumper between super capacitor and RTC,or add voltage monitor circuit if super capacitor voltage below the setting value turn off it.

[dominusdrr]

I think it is a cumbersome solution about the jumper, since the user doesn't have access to the internal hadware, and the other solution involves adding more things to the hardware that is already designed.

[guoweisun]

You have to add hardware circuit to minitor super capacitor voltage or switch it into battery!