I am using two STM32F405's to read a switch and have some diagnostics.
I interface this to an analog input on one MCU and a digital input (no pull up/down) on another MCU.
However, I have cross-talk with the neighboring analog channels and more severe, also disturbances when doing radiated immunity tests (100 V/m).
The circuit is like shown (actually there are several identical interface circuits):
The ADC is running continuous scan mode, 28 cycles, 10 MHz.
It seems that decreasing capacitor at AIN (C3) to e.g. 100 pF improves the immunity. So far I have only focused on the filter function R2, C3/C4, but is it more important to have small capacitance close to the MCU?
When reading datasheet and application notes they say capacitor should be in pico farad range.
Datasheet states a maximum value for R2 to be less then 65 kohm (calculated from equation 1). Would the performance EMC and cross-talk wise be improved by using a lower resistance value?
I there a way to improve cross-talk by delaying time from setting internal MCU multiplexer to start of conversion?
