4.1.3 Power Switch

The device features a power switch between VBAT and VDD3V3. Its output, VDDBU, powers the backup area.

The power switch features a Manual mode controlled by software to select VBAT or VDD3V3 (default at power-up). An Automatic mode is also available when used with the VDD3V3 Supply Monitor (SMVDD3V3) as a fold-back source to switch VDDBU to VBAT in case VDD3V3 is falling under the SMVDD3V3 threshold. A second Automatic mode (not user programmable and not correlated to the SMVDD3V3) is available, in case of the power switch is on VBAT and VBAT is falling, the switch is commuted automatically to VDD3V3. Refer to the sections Supply Controller (SUPC) and Reset Controller (RSTC) for details on the power switch.