Two inductor in series in DC/DC regulator ckt of nRF51 and nRF52.

[hamidh]

why there are two inductor in series in DC/DC regulator ckt, is that inductor value is so critical?instead can we use only one inductor? what are critical selection parameter for inductors and capacitor used in DC/DC regulator ckt and RF section of nRF52 chip.

[MartinBL]

The reason is that big 10uH inductors behave differently than small 15 nH inductors. The 10uH inductor is bad at filtering out the higher frequencies. That is why we have added a smaller one to take care of these. Leaving out the 15nH inductor will reduce your RX sensitivity.

It might seem unnecessary, but it is a common tactic in electronics and applies to capacitors as well. If you look at the reference designs you will notice that there are large and small capacitors too.

Here is a more thorough explanation and here is a very cool video.