15 µF at 2.5 V in 0805 — the ESR is the decoupling bottleneck
The TAJR156M002RNJ: This is a 15 µF, 2.5 V rated molded tantalum from the TAJ series, in an 0805 (2012 metric) case. The 4.1 Ohm ESR at 2.5 V means the ripple current capability is limited — for a 100 kHz switching regulator output, the AC ripple current through the cap generates I²R losses that heat the part. On a 2.5 V core rail, every 10 mV of ripple translates to roughly 2.4 mA of ripple current; at 4.1 Ohm that is 24 µW of self-heating, negligible for a single cap, but in a bank of four the combined ESR drops to 1 Ohm and the ripple sharing becomes uneven without matched ESR grades.
For an avionics black box that sees -40 °C cold soak and +105 °C under full load, the 125 °C ceiling gives 20 °C of margin above the hottest internal ambient. The same part works in a downhole tool rated to 125 °C — no need for a separate high-temp BOM line.
0805 case, size code R — layout fit and footprint
0805 (2012 metric) footprint, size code R per EIA-535. Seated height is 1.20 mm max — fits under a 1.5 mm clearance shield or on the underside of a 1.6 mm board with 0.4 mm clearance to the next PCB. The land pattern is the standard 0805 tantalum pad: 1.0 mm × 1.2 mm per terminal, 1.0 mm gap. No via-in-pad required.
Active production — sourced per RFQ
The ±20 % tolerance and 2.5 V rating are standard for this series — no special screening or date-code hold.