MicroPython Forum (Archive)

The schematic shows a placement for a rechargeable RTC backup battery Seiko MS414GE-FL26E. The datasheet (page 5) shows a series charging resistor of 2000Ω whereas the schematic has R2 = 100Ω. Is this OK?

The diode used was selected to provide minimal reverse current. Unfortunately this means pretty high forward voltage. Therefor a pretty low current limiting resistor has to be used.
Note that the battery isn't installed as it cannot re-flowed but has to be hand soldered. It is also pretty hard to get with recent Li transport restrictions.

I'm surprised. The diode only becomes reverse biassed when the Li cell is supplying the RTC. The consequence of reverse leakage is merely to discharge the cell. I'd expect the reverse leakage current of a silicon diode at 3.3V to be much lower than the current consumption of the RTC.

The datasheet with its 2000Ω resistor presumably references exactly this application. Or am I missing something?

Thanks Pete. The schematics for WBUS-DIP28 are now updated to note that the current limiting resistor is not populated by default, and that the user should pick one that matches the specs of the battery used.