Charge pump step-up for low-power rails
The LTC3221EDC-3.3#TRMPBF: Switching at 600 kHz, the external flying capacitors stay small (typically 0.22 µF to 1 µF), keeping the total BOM footprint tight for space-constrained portable designs. No synchronous rectifier is integrated — the output diode is external. A Schottky with low Vf (e.g., 0.3 V at 100 mA) keeps conduction loss in check; the charge pump's output impedance rises with the diode drop, so the diode choice directly affects the available load current at the regulation point.
Package and thermal: 6-DFN with exposed pad
The supplier device package is 6-DFN (2x2), so the stencil aperture for the centre pad should match the datasheet recommendation to avoid voids under the die attach pad.
Temperature grade and operating range
The input minimum of 1.8 V means the part starts from a nearly depleted Li-Ion cell (3.0 V nominal, down to 2.7 V cutoff) or two alkaline cells at end-of-life (1.0 V each under load). The 4.4 V maximum input limits it to single-cell Li-Ion or 2-3 cell alkaline/NiMH — not a 5 V rail.