680 nH, 190 mA — the three numbers that decide the filter fit
The LQH31MNR68K03L is a Murata drum-core wirewound inductor in the LQH31 series, 680 nH ±10% with a 190 mA current rating and 938 mOhm max DCR. These three numbers are the ones that decide whether this part fits a given DC-DC filter or RF decoupling position: the inductance sets the corner frequency, the current rating sets the load it can carry before saturating, and the DCR sets the resistive loss and temperature rise. The 190 mA rating is the continuous DC current at which the inductance typically drops by 10% — above that the core begins to saturate and the inductance falls off, so the actual usable current in a power rail filter is lower than the headline number. The 938 mOhm DCR at 25°C means a 190 mA DC bias produces about 34 mW of I²R loss; in a 1206 package without a thermal pad, that heat dissipates into the board copper, so the ambient temperature and adjacent heat sources matter.
Q at 25 MHz and self-resonant frequency at 160 MHz
A Q factor of 30 at 25 MHz tells you the inductor stores energy efficiently at that frequency — useful for tank circuits or impedance matching in the HF band. The self-resonant frequency of 160 MHz is the point where the inductor's parasitic capacitance cancels the inductance; above that the component behaves capacitively. For a 680 nH part, 160 MHz SRF is typical of a wirewound construction in a 1206 body and means the inductor is usable as a filter element well into the VHF range, as long as the operating frequency stays below roughly 80 MHz (half the SRF) to keep the impedance predominantly inductive. The inductance is tested at 1 MHz, which is the standard test frequency for values in the hundreds of nanohenry range — the measurement condition is not the operating condition. The actual inductance at 25 MHz or 100 MHz will differ slightly due to core losses and skin effect, but the Q spec at 25 MHz gives a reliable figure for the loss at that frequency.
Last Buy — the sourcing window is closing
Murata has marked the LQH31MNR68K03L as Last Buy. This is the final procurement window — once Murata closes the last production run, the part will no longer be available through authorized distribution. For a BOM that already carries this inductor, the immediate action is to secure lifetime buy quantities or identify a functional replacement before the last-buy deadline passes. The 1206 footprint and 680 nH ±10% value are common enough that a parametric search across other Murata series or other manufacturers (TDK, Taiyo Yuden, Coilcraft) will yield drop-in candidates, but the DCR and current rating must be matched to avoid a re-spin or a thermal issue.
1206 footprint, ferrite core, unshielded
The ferrite core material gives good inductance stability over temperature and frequency for a wirewound part in this value range. Unshielded means the magnetic field radiates outside the component body; in a dense layout, adjacent traces or other inductors may couple, so keep a clearance of at least one component width to nearby sensitive circuits. For under-hood or engine-bay applications, a different Murata series with a higher temperature rating would be needed.