Sharing ADC and GPIO PADs that supports 5V tolerant

[Fred573]

Hello everyone,

I have a question that I would like to share with you:

I am currently working on a project where I want to share the input PAD of an ADC with the GPIO's PAD. The main purpose behind this is to save costs. The GPIO PAD supports 5V tolerance, while the ADC only allows a maximum input voltage of 3.6V. I have implemented a switch (transmission gate) between the ADC and the PAD, which allows me to turn off the ADC when it is not in use. However, I have a concern regarding the situation where the PAD voltage is 5V, as it could potentially conduct through the PMOS of the switch and damage the ADC. Could someone please guide me on how to address this issue?

Thank you all for your assistance.

Best regards,
Fred

[PCB.Wiz]

Is the ADC on the chip, or external ?
Usually on-chip ADCs with 5V tolerant pins, are also 5V tolerant, even if they can only measure up to 3.3V Vcc.

If the ADC is external and the pin can drive to 5V, you will need protection.
The simplest can be a series resistor, and you could add an analog switch if micro-power is needed, or if you need other ADC pins reading.
(clamp currents can disturb adjacent ADC pins )