Capacitance and voltage for bulk decoupling
The TAJX227K004RNJ: Rated 220 µF at 4 V with ±10% tolerance, this TAJ-series molded tantalum provides the bulk capacitance for a 3.3 V or lower rail where the voltage derating rule (typically 50% margin) is satisfied — 4 V rated part on a 2.5 V rail leaves 1.5 V headroom. The 900 mOhm ESR at 100 kHz sets the ripple current rating and self-heating — for a 500 mA load transient, the voltage droop is I × ESR = 0.45 V, so the downstream regulator must have enough loop bandwidth to recover before the output dips out of tolerance.
Housed in the 2917 (7343 Metric) case size, size code X, with dimensions 7.30 mm × 4.30 mm and a seated height of 1.50 mm — the low profile fits under a 2 mm board-to-board clearance, but the narrow 0.059" height means the reflow paste volume must be controlled to avoid tombstoning.