why two inductors for SMPS on P-NUCLEO-WB55

[WQ]

There are two inductors, L1 10uH and L5 10nH, in series for SMPS circuit in P-NUCLEO-WB55 design. Why is that? is the sequence affective (smaller L5 coming out of VLXSMPS pin)? Thanks. -wq

[AlbertoGarlassi]

Maybe because bigger inductors have bigger parasitic capacitance and losses at high frequency. In this schematic L5 works OK for the higher armonic content of the PWM and for these frequencies it isolates L1. I guess efficiency is somewhat higher.

L5 should be closer to the switching pin, in this way capacitance to ground is minimized.

[AScha.3]

i think, the L1 and L5 are there for :

L1 is for the smps , power inductance;

L5 is EMV related, because this chip has BT receiver and so any noise in the 2.4GHz range should be suppressed.

[WQ · Accepted solution]

It is mentioned in AN5165. -wq