L28A is a NiZn ferrite with an initial permeability (μi) of approx. 2800 — the highest of the NiZn grades in this volume — a saturation flux density (Bs) of approx. 250 mT at 25 °C (160 mT at 80 °C) and a Curie temperature above 80 °C. The highest permeability yields the L family's highest low-frequency impedance, meeting conducted-noise targets in the hundreds-of-kHz range with the fewest turns; the coercivity of only about 8 A/m keeps hysteresis loss minimal, and the high resistivity and long-term stability sustain suppression on communication lines. Typical uses are low-frequency EMI filters, signal-line common-mode inductors and power-inlet suppression. Its Curie temperature, above 80 °C, is the lowest of the family — intended for room-temperature environments; move to L22A or below where self-heating or ambient temperature is significant. L22A is the adjacent step (nominal μi 2800 vs 2200, with overlapping tolerance bands): pick L28A for maximum low-frequency impedance, L22A for extra temperature margin.