VDD_RTC is connected directly to the onboard PMIC. Backup cells must provide a voltage in the range 2.5V to
3.5V. These will be charged with a constant current (CC), constant voltage (CV) charger that can be configured
between 2.5V and 3.5V CV output and 50uA to 800uA CC. The following backup cells may be attached to this pin:
Super Capacitor (gold cap, double layer electrolytic)
Standard capacitors (tantalum)
Rechargeable Lithium Manganese cells
regulator-min-microvolt = <3000000>;
regulator-max-microvolt = <3000000>;
in spmic_ldo4: ldo4 can change the RTC output voltage.
So how to configure the charging current to 800uA or higher?
If use a 0.22F super cap , how long can the RTC time be keep.