The TPS65510 offers a suitable solution for power switch to select the main battery or the backup battery.

This device automatically selects the power path. It depends on the voltage level of the VO_BT pin. When the main battery is removed, the power path of the VOUT pin is automatically changed from the output of 3.3-V low droppout (LDO) voltage regulator to the backup battery.

The backup battery is charged from the power path of the VRO pin (output of 3.3-V LDO) via an external diode and resistor. The input of the LDO voltage regulator comes from the internal boost converter.

The 1.2-V output LDO and 1.8-V output LDO voltage regulators have a enable pin, V_CTRL. If these outputs are not necessary, V_CTRL should be connected to AGND to save power consumption.