2.2 µF at 20 V — the BOM-fit check
The TAJS225K020RNJ: The 2.2 µF capacitance at a 20 V rated voltage in a 1206 case is the first fit criterion for this TAJ series molded tantalum. The ±10% tolerance means the actual capacitance at the rail sits between 1.98 µF and 2.42 µF — enough margin for decoupling or timing circuits that need a predictable value.
4.5 Ohm ESR — what it means for ripple and heating
The 4.5 Ohm ESR is the dominant thermal contributor in this capacitor. For a given ripple current I, the internal power dissipation is I² × 4.5 Ohm. If the circuit draws more than a few tens of mA RMS ripple, check the self-heating against the derating curve in the datasheet.