Inductance and current rating for DC-DC filtering
The LQH43NN330K03L is a 33 µH drum-core wirewound inductor rated for 270 mA DC current. At that bias the inductance holds within tolerance; push beyond 270 mA and the ferrite core begins to saturate, dropping the effective inductance and raising ripple current in a buck output stage. Maximum DC resistance is 1.2 Ohm, which at 270 mA produces about 87 mW of I²R loss — negligible for most power rails but worth derating if the inductor sits in a confined enclosure above 85°C ambient.
Frequency limits and Q factor
Self-resonant frequency is 12 MHz. Above that the parasitic capacitance across the winding dominates and the part behaves capacitively — keep the switching frequency or the fundamental ripple frequency below 12 MHz for inductive behaviour. Q factor is 35 at 1 MHz, typical for a ferrite-core wirewound in this inductance range. The Q peak sits near the SRF; if the circuit operates far below 1 MHz the AC losses increase and the effective inductance shifts slightly.
Package and reflow profile
The unshielded construction means the magnetic field extends outside the body — keep sensitive traces or other magnetics at least one package width away to avoid coupling. Supplied on tape and reel in cut-tape quantities. The ferrite core is brittle; avoid excessive board flex near the part after reflow.