What this TAJ tantalum is and where it sits on the board
The TAJY157K004RNJ: This is a molded tantalum capacitor from the TAJ series, 150 µF at 4 V with ±10% tolerance, in the standard 2917 (7343 Metric) case size — the same footprint as the industry-wide D-size tantalum chip. The 400 mOhm ESR is moderate for this capacitance and voltage — it handles ripple current in a bulk decoupling role without excessive self-heating, but it is not a low-ESR part for high-frequency switching supplies.
Derating and reliability — the 4 V rating in practice
Tantalum capacitors are sensitive to voltage derating: a 4 V rated part should be applied on a rail no higher than 2.5 V to 3 V to avoid field failures from surge current or reverse bias. The Y case code (7.30 mm x 4.30 mm x 2.00 mm) is the standard D-size footprint — it fits the same land pattern as the AVX TAJ D case and the Kemet T491 D case, so a BOM swap is straightforward.