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Hello,
I have developed 15 W power supply powered by a 1-cell LiIon battery. Due the mechanical constraints of the enclosure and to minimize the EMI, the design is compact and all the power components are close each other to minimize path lenght and loop areas. Particularly the 2 inductors are next each other.
The noise is audible only at low loads, when the operation is in PFM discountinuous mode. When it passes to continuous mode, the noise stops.
I have used 2x47 uF MURATA ceramics capacitor as input decoupling network: adding smaller capacitors, i.e. 22 nF + 10 pF reduces the noise but it is still audible to the most sensible ears.
I would like to know if someone has had a similar experience and if there is a root cause that can be used to understand how modify the circuit or the layout.
Thanks for the reply.
Hello, sorry for delay but my Company was closed for Spring Festival holiday.
The waform are below, the single PFM packet and the repetitive signal.
About the schematic, I am sorry but currently I cannot share due company policy. In any case it is a standard circuit with 2 independent inductors with same value of 3,3 uH, at switching frequency of 1 MHz.