Drum-core wirewound for filtering and decoupling
The Murata LQH31MN390J03L is a 39 µH unshielded wirewound inductor in the LQH31 series, built on a ferrite drum core. It is a surface-mount component in the 1206 (3216 Metric) footprint, suited for general-purpose filtering, DC-DC output smoothing, and signal decoupling where the 55 mA current rating and 7.2 Ohm DCR fit the load budget.
Frequency response and Q factor
The self-resonant frequency is 11 MHz, above which the inductor behaves capacitively — keep the operating frequency well below this for inductive impedance. The Q factor is 40 at 2.5 MHz, indicating moderate energy storage efficiency in the low-MHz range, typical for a ferrite-core wirewound part.
The unshielded construction means magnetic flux radiates from the core — keep sensitive traces or other magnetics at least a few millimetres away to avoid coupling.
Temperature grade and operating range
The ferrite core material maintains inductance stability across this range, though DCR increases with temperature — budget the 7.2 Ohm cold value plus the copper temperature coefficient when calculating I²R losses at the high end.