Thank you both for your answers! Finnaly with ADC.ATTN_11DB it works!

@MrMarty77 Only ADC1 is supported at the moment, the core ESP32 SDK doesn't support it yet, it may take a while: https://github.com/espressif/esp-idf/pull/466 Fyi, we're a bit hesitant to make ADC2 available because it is also used for pretty important control loops inside the WiFi (and maybe BT, I don't remember) drivers. We want to make sure there's no chance of these and the user ADC calls to interfere with each other.