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RF matching network _ Z values _ nucleo RF performance

Senior II


I started a Circuit/PCB design with STM32WL55CCU (UFQPN48) to work at 433MHz.

I was referred to ST design for low band/Hight power and to AN5457.

But I am style missing for some information:

  • What is the PA impedance at 433MHz for UFQPN48 package?
  • In AN5457, the recommended value of L6 between 300MHz and 500MHz is 68nH. Why in all ST circuit design (low band) L6 is set to 56nH?
  • Is the order of C4 and L3 has any influence on the circuit (some time C4 is before L3, and some time C4 is after L3)
  • In the different ST circuit design, the CLC PI filter an matching (C8/L4/C7) is not accorded to 50ohm. Is it normal?


After making some test with the nucleo board wl55, I cannot find the same range like I had with other RF433 module. It is look like RF circuit is not optimised or …. Is anybody have the same observation?

Associate II

I'm having the same questions about PA output impedance at 433Mhz and I also noticed the L6 discrepancy. Would be nice to have some answers...