ESD protection for external button(human touch activated)?

[MikeLemon]

Hello,

In my next project I plan to conductive pads as buttons(that are exposed for humen touch to interacte with the) one is connected to ground and the rest will connect directly to the nrf52832 chip with an internal pullup resistor.

Now the question is how safe this setup would be against ESD as there will be a direct contact with the man and the pad?

also my other concern is if two input pads would short out accidentally would any damage be caused to the chip? if so what could be a solution for it? tested this one with arduino and it didn't seem to do much but maybe it's different for that one.

Thanks for your time!

[bjorn-spockeli]

All GPIO pins on nRF52 have ESD diodes to VSS and VDD, they are reversed biased diodes, and will start to conduct if the GPIO is pulled above VDD or below VSS.

The nRF52832 is rated for the following charges, depending on which package you're using

QFN48 6x6mm package

ESD HBM (human body model) 4 kV  
ESD CDM (charged device model) 1000 V

WLCSP48 3.0x3.2 mm package

ESD HBM (human body model) 1 kV  
ESD CDM (charged device model) 500 V

However, the typical static charge that a human body can hold is usually in the 1 -10kV, but might be as high as 25 kV, see below quote from Wikipedia.

Maximum potential commonly achieved on human body range between 1 and 10 kV, though in optimal conditions as high as 20–25 kV can be reached

Hence, you should add some kind of protection, e.g. adding a series resistor to limit the current going in to the chip.

[MikeLemon]

Ok thanks so you say it is safe toe expose the pins to the human touch?