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FAdar.1
Associate II
Feb 25, 2021 11:20 PM UTC
Solved

Are 3.3pF caps needed on PB10, PB11, and PC5 (sensitive GPIOs) if they are not connected to anything?

This is for the STM32WB5MMG, on page 11/31 of the datasheet.

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Remi QUINTIN
Remi QUINTINBest answer
ST Technical Moderator
Feb 26, 2021 3:49 PM UTC

If PB10, PB11, and PC5 are no connected, the 3.3pF are not needed.

It is only when tracks are connected to those 3 sensitive pins that the capacitors are recommended to avoid propagation of noise along the board.

2 replies

Vangelis Fortounas
Associate II
Feb 26, 2021 12:30 AM UTC

Hello

why not connect it to GND?

3p3 capacitance (reactance is 20 ohms) is too low and makes someone to suspect that theese three GPIOs are succeptible to 2.4GHz causing various, observed already effects

Remi QUINTIN
Remi QUINTINBest answer
ST Technical Moderator
Feb 26, 2021 3:49 PM UTC

If PB10, PB11, and PC5 are no connected, the 3.3pF are not needed.

It is only when tracks are connected to those 3 sensitive pins that the capacitors are recommended to avoid propagation of noise along the board.