I’m not sure, let me do some research on this. I’ll let you know if I’m able to find more information on it.
I measured V_VBAT_BKUP pin current like this:
The result shows when VSYS power is On, V_VBAT_BKUP require 1.3uA@2.5V.
If VSYS power is Off, V_VBAT_BKUP require 8.4uA@2.5V.
Next, I will try to find the minimum voltage of RTC working.
However it's difficult to measure correctly, so I expect your information.
RTC current is 10 microamps when all power is removed.