Physical pullup on input when VDD=0V is not as expected

[kuhatovuk]

Hello,

I placed a simple physical pullup to 3.0V of 2kOhm on ESP32-Pico-D4 pin 5 SENSOR_VP but when ESP32 is not powered, I read 0.6V instead of 2.8V.

Is it possible to have a correct pullup when device is off ?

Or is the correct way to have the device off to have VDD pins high and only EN pin low ?

Thank you,
kuhatovuk

[ESP_Sprite]

There are internal ESD diodes (actually snapback circuits, but the idea is the same) on each pin, that short any voltage on that pin above Vdd to Vdd. So if your Vdd is 0V, it will short your pullup resistor effectively to Vdd=0V. That's what you're seeing here. The pullup will do the right thing as soon as you restore 3.3V Vdd to the chip.

[kuhatovuk]

Thank you ! Is there a trick to do this when the device is off or should I power it on at all time and use EN to turn it on/off ?

This line is a regular button for ESP32 but also a switch to turn on power to all sensor chips and ESP32.