1.2 mH at 45 mA — the DC bias ceiling
The LQH43NN122K03L is a drum core wirewound inductor from Murata's LQH43 series, rated 1.2 mH at 45 mA. That 45 mA is the DC current at which the inductance typically drops by 10% — push beyond it and the ferrite core saturates, collapsing the inductance and turning the part into a resistor. For a 1.2 mH choke in a low-current filter or DC-DC output stage, the 30 Ohm max DCR means the I²R loss at 45 mA is about 60 mW — negligible in most circuits, but the voltage drop across the winding at that current is 1.35 V, so the downstream rail sees that much less headroom.
Self-resonant frequency and Q factor
The self-resonant frequency (SRF) is 1.8 MHz. Above that frequency the inductor behaves capacitively — the inter-winding capacitance dominates. For a filter or resonant circuit, keep the operating frequency at least a decade below 1.8 MHz to stay in the inductive region. The Q factor is 40 at 252 kHz, which is moderate for a wirewound ferrite core; it tells you the ratio of reactance to resistance at that test frequency, so the component's AC loss is about 2.5% of the stored energy per cycle at 252 kHz.
1812 footprint, unshielded — layout considerations
It is unshielded, so the magnetic field radiates into the surrounding PCB area — keep sensitive traces or other magnetics at least one package width away to avoid coupling.