1 mH filter inductor for low-current signal and power paths
The Murata LQH43NN102K03L is a 1 mH drum-core wirewound inductor in the LQH43 series, rated for 50 mA continuous with a maximum DC resistance of 25 Ω. At 50 mA the I²R loss is 62.5 mW — the thermal rise stays under 10°C in free air, but a tight layout with adjacent heat sources should budget the self-heating into the local ambient. The unshielded ferrite core means the stray field couples into nearby traces and components — keep a keep-out zone equal to the part height (2.8 mm) on adjacent copper layers to avoid eddy-current losses in ground planes or detuning in adjacent LC tanks.
Frequency response and Q factor — where this inductor works
Self-resonant frequency is 2 MHz; above this the inductor behaves capacitively. The Q factor is 40 at 252 kHz — useful for resonant tank circuits or EMI filtering in the low hundreds of kHz, but the Q drops off above 1 MHz as the core losses dominate. Inductance is tested at 1 kHz, which is the standard low-frequency reference. At the self-resonant frequency the effective inductance drops to zero — a filter designed at 1 MHz sees a fraction of the nominal 1 mH, so the cutoff frequency shifts. Derate the inductance by 20% at 500 kHz for a conservative filter pole calculation.