for a project of mine i want to use the DS3231 RTC clock.
Not as the off-the-shelf module, but rather integrated into my own PCB.
So the idea is to recreate this circuit of the original module.
Unfortunately, the charging is not really a well-designed circuit, because even when using a suitable rechargable Li-Ion battery, the voltage might be around 4.5V at the battery terminal (after 0.5V drop of the diode) and therefore can damage the battery cell.
Since i do want to use the backup option, removing the circuit alltogether is not an option for me.
My first thought was to integrate a voltage regulator to lower the voltage to 4.7V (before diode), but i could only really find 3.3V and 5.0V versions, so both are not really ideal.
Do you have any other idea on how to easily adapt this circuit so it provides a long term reliability of the backup system?
I believe that the diode and resistor are there to allow the DS3231 to operate without the CR2032 battery. If you want to have battery backup, then just eliminate the diode/resistor and use the 2032 battery for the backup. The battery will last 10 years of use without any power applied to VCC.
So you are planning to use an LIR2032 as the battery, or some other rechargeable battery? If not, you shouldn't have a charging circuit at all.
Also, I think the LIR2032 has a capacity of around 38mAh, while the CR2032 is about 210mAh. So depending on your situation, you might really not be better off using a rechargeable battery. In any case, the DS3231 will run at about 1-2uA keeping time when powered at Vbat. A CR2032 will last a long time at that rate.
