ESD protection GPIOs pins

[Nico3]

I need to assign  8 GPIOs (4 I/p + 4 o/p) for membrane keypad pushbutton circuit. 

I am worried about ESD protection of GPIOs. Please suggest  STM parts for ESD protection best suited for use purpose.

Kindly let know if I can select any  pins or there are some more tolerant GPIOs. 

[raptorhal2]

<best suited for use purpose> A better definition would be helpful.

What sources of ESD are you concerned about?

What is the design ? For example, is the Keypad on the same PCB as the F4, or is there unshielded cabling between them?

The F4 datasheet should specify the F4 internal GPIO pull up and pull down resistors.

[Nico3]

PCB will be enclosed in metalic box. Keypad will be outside for user interface. I am concerned about

ESD  from Human finger and transmitted via keypad buttons to GPIO pins

[raptorhal2]

Probably a benign environment. The keys are probably electrically isolated from the electrical contact, and you can put an RC circuit on each wire to the GPIOs for key bounce suppression and that will help also.

Littlefuse at

https://www.littelfuse.com/technical-resources/application-designs/circuits/circuit-protection-keypad-solutions.aspx

has some information and an IC solution for keypad ESD.