Hello,

In the datasheet of the 1.5 uH inductor "7440450015" from Würth Elektronik there is the typical impedance characteristics curve which I also attach here. However the impedance values well below the self-resonance frequency does not correspond to the real inductance of the inductor.
For example at 1 MHz the impedance is 5 Ohm. So from L = X/(2*pi*f) we have 0.79 uH, much different than what it should have been. What am I doing wrong? The curve actually considers the magnitude of Z and not imaginary part of it, but at 1 MHz the real part of it should be negligible, so shouldn't my calculation above be correct?

 

It's possible that it's an error in the data sheet. I'd recommend reporting it to the manufacturer and seeing what they say.

 

yup... seems way off... at 1MHz R=0.09Ohm, Xl=9.4 Ohm so to get impedance Z=5 Ohm it would also need to have Xc=4.4 ohm which would be parasitic capacitance of some 36nF. but that is if one considers sine wave. pretty sure these inductors are meant for SMPS so waveforms and results could be different

 

Are either of the graphs plotted from accurately measured results? Using accurate measuring packages? Or just plotted from a few calculated values? Every inductor has some amount of resistance and some amount of capacitance between turns. And other variables unknown to most of us.

 

Are either of the graphs plotted from accurately measured results? Using accurate measuring packages? Or just plotted from a few calculated values? Every inductor has some amount of resistance and some amount of capacitance between turns. And other variables unknown to most of us.

As WBahn said, it seems to be an error in the datasheet, because when simulating the Spice model of the component created, again, by Würth Elektronik with all its parasitic capacitance and resistances specified, the impedance-frequency behavior that I am getting is much closer to what I was expecting.

 

It may also possibly be that there is an error or an omission in the spice model. That has been known to happen.