nRF54Lxx - reset circuitry

[simonk]

Dear all,

I am wondering, what is the reason for C13 being 3.9pF for QFN package, while there is no capacitor on WLCSP reference design? Could we use like 10nF instead? From what I see, this is a part of low-pass filter for RESET line from external circuitry (programmer).

Typical reset circuit on microcontroller is 10k pull-up + 10 or 100nF to GND, but there is no recommendation for that. Obviously, there is some other reason behind selected value.

Many thanks for your answer.

[Turbo J]

Look at the pin numbers. Reset is right next to the antenna.

That means you must be very careful, that cap is likely black HF magic in order to prevent ANT influencing the Reset signal. Larger MLCC may not be effective at 2.4 GHz.

The WLCP reference may have different magic in the layout which may be relevant here.