# LC circuit of buck converter in nRF8001 datasheet

In the datasheet of the nRF8001, they specify in the reference schematic (page 51) the LC circuit to use with the integrated DC/DC converter (see below).

Why is there a small inductor L5 in series with L4?

Is it related to the self resonant frequency of the inductors? That was my first thought, but the 10nF inductor specified in their integration note (Taiyo Yuden LBMF1608T100K) has a minimum self resonant frequency of 32MHz. The exact frequency of the nRF8001 buck converter is not specified, but it seems to be well above the frequency of any buck converters.

• That self-resonant frequency is also a long way below the Bluetooth operating frequencies. So the second inductor may be required to increase impedance at those frequencies. – user_1818839 May 24 '16 at 20:46
• @BrianDrummond Yes, indeed the SFR of L5 is close to Bluetooth frequencies, so i think it is the reason. Any idea why exactly it is needed? – Adrien Descamps May 25 '16 at 5:32