15 µF, 20 V, 1.7 Ω ESR — bulk decoupling for a 20 V rail
The TAJC156K020H: 15 µF at 20 V with a 1.7 Ohm ESR — this tantalum sits on a 20 V rail as bulk decoupling, where the capacitance stores enough energy to hold the rail up during a transient, and the ESR limits the ripple current heating. The 20 V rating gives 20 % derating margin on a 16 V rail, which is standard practice for tantalum reliability. The 1.7 Ohm ESR is the self-heating floor — at the ripple current the part will see in a switching regulator output, that resistance converts current into temperature rise. Keep the RMS ripple current below the datasheet limit to stay within the 125 °C ceiling.
The tantalum dielectric holds capacitance across the band — no derating curve needed until you approach the voltage limit at high temp.
You can order it against the BOM without stockpiling or scrambling for a second source.
2312 case C — footprint and rework
Case C (6.00 mm x 3.20 mm) is a mid-body tantalum — bigger than A/B for the 15 µF capacitance, but smaller than D/E so it fits a dense layout without hogging board area. The 2.80 mm seated height clears most low-profile enclosures. Under a hot-air station the case body heats evenly; the solder joints reflow cleanly at 260 °C peak per J-STD-020. No hidden thermal pad to worry about.