1.8 mH in a 1812 footprint — what the ratings mean for the BOM
The LQH43NN182K03L is a drum-core wirewound inductor from Murata's LQH43 series, delivering 1.8 mH ±10% in an unshielded 1812 (4532 Metric) surface-mount package. The 35 mA current rating is the DC bias current at which the inductance typically drops by 10% — stay below this for the nominal value to hold across the operating range. A 45 Ohm maximum DC resistance (DCR) means that at 35 mA, the resistive loss is 1.6 V and 55 mW — the self-heating is modest, but the voltage drop matters in low-voltage rails where the inductor sits in series with the supply.
Self-resonant frequency and test conditions
The self-resonant frequency (SRF) is 1.5 MHz — above this point the inductor behaves capacitively, so the part is intended for filtering and energy storage in circuits switching below roughly 500 kHz, where the impedance remains inductive. Inductance is tested at 1 kHz, and the Q factor is specified at 40 measured at 252 kHz — the Q peaks near the SRF, so at lower frequencies the effective Q is lower than the listed value.
The ferrite core material saturates above the rated current; the unshielded construction means the stray field couples into adjacent traces — keep sensitive analog or RF circuits at least one package width away.