390 µH at 90 mA — dc bias limit before core saturation
The LQH43MN391J03L is a 390 µH drum core wirewound inductor in Murata's LQH43 series, rated for 90 mA continuous current. That 90 mA figure is the dc bias current at which inductance typically drops by 10% — exceeding it pushes the ferrite core into saturation, and the inductance collapses.
9.7 Ohm DCR — copper loss budget for the BOM
Maximum dc resistance is 9.7 ohms. At 90 mA, I²R loss is 78 mW — negligible in a power stage but significant in a low-current signal path where the voltage drop across the inductor (0.87 V at full rated current) eats into the headroom. The Q factor of 40 at 796 kHz tells you the ac-to-dc loss ratio: at that test frequency, the inductive reactance (1950 ohms) is 40 times the effective series resistance, so the component behaves as a clean inductor rather than a lossy choke in that band.
Unshielded 1812 — magnetic field couples to nearby copper
This is an unshielded drum core in an 1812 (4532 metric) package. The open magnetic structure radiates a fringe field that couples into adjacent traces or other inductors — keep a clearance of at least one part width (4.5 mm) from sensitive analog loops or second-stage filters. The ferrite core material sets the self-resonant frequency at 3.3 MHz; above that the part looks capacitive, so the useful band stops well below 3.3 MHz for most filter designs.