ADC pin protection

[ChiBit]

Hi,

I am using the nRF5340 chip and I am switching a load with some parasitic capacitance (estimated at ~0.5nF) and I get voltage swings that could exceed Vdd and go below GND.  I was wondering if the analog pins (AIN0-AIN7) have any built-in protection diodes?  If there are protection diodes, will the diodes be sufficient protection?

Thanks

[Hieu]

Hi ChiBit,

There are some protections against ESD, but it is not recommended to rely on this for input outside of the absolute maximum ratings like you are describing.

Below is a quote from one of my seniors who is more experienced in this topic:

If a pin voltage goes outside of VDD/VSS rails there is a risk of forward biasing internal p-n junctions, injecting noise on rails and distorting signal. So rule of thumb is that it's not allowed. [...] (It's) hard to tell where the limit is. We recommend to avoid it.

Hieu

[ChiBit]

Hi Hieu,

Thanks for the information.  However, it would be of great help if you could provide pin diagrams that show the pin protection and any details on the ESD protection, because I can use other techniques such as current limit resistors to solve the problem.

Point of note is that I have excessive inductance in the circuit that is causing the voltage swings and knowing the details of the pins and ESD protection can save me time.

Your help would be greatly appreciated

ChiBit

[Hieu]

Hi Chibit,

Unfortunately, we do not release such details. I am very sorry for being unable to help.

Hieu