What this buck-boost does that a simple LDO cannot
The TPS63012YFFT is a buck-boost regulator that maintains a regulated output when the input voltage swings above or below the target — exactly what a Li-ion battery does as it discharges from 4.2 V down to 3.0 V. The 2A switch rating means it can deliver a full 2 A to the load when the input is low, not just when it is above the output.
Output voltage selection and the programmable pin
The output is programmable via a logic pin to one of two fixed voltages: 2.9 V or 3.4 V. That covers the common rails for a 3.3 V logic supply (3.4 V setting) or a 2.9 V core rail. The input range from 2 V to 5.5 V means it works from a single-cell Li-ion through a 5 V USB bus.
Package and layout reality for the 20-DSBGA
The 20-DSBGA package is a 0.4 mm pitch wafer-level chip-scale package. That means the PCB land pattern is the die footprint — no mould compound overhang. The thermal vias under the package are not optional; the junction-to-board thermal path relies on them. The 2 A output at 2.4 MHz generates enough copper loss that a 2-layer board with solid ground plane under the DSBGA is the minimum viable stack-up.