[SOLVED] Not Connected PINs in ICs

[H2M]

Hi everyone.
I have made my own board. I use W5500 for ethernet communication and i use stm32f407 for host MCU. The W5500 have many not connected pins. what should i have done with them? i must left them floating or pull up or pull down? Also many of my stm32f407 pins are unused. what should i have done with thems?
Thanks

 

[barry]

If they're inputs, you can pull them down. It also depends on the function of the pin. Outputs can float (obviously). Some devices have internal pulls, so you don't have to worry about it.

 

[KlausST]

Hi,

If you find in the datasheet at a pin description "not connected", then this really means it has no internal electrical connection.
No need for an electrical connection on the PCB - unless otherwise noted in the datasheet.

But sometimes the datasheet tells you have to connect them to GND - for noise reduction or higher ESD immunity...
Or it says to connect them to a copper plane because of thermal reasons
Or any other recommendation..
Then follow the datasheet recommendation.

But maybe you mean that you don't use some of the (internally connected) pins...this is something different...
A general rule for this situation: Don't leave any (unused) input pin floating - neither a digital nor an analog input pin.
"Not floating" does not mean you have to connect them externally - in case you can "program" the pin as "non floating" (usually with microcontrollers) then this is OK. It just needs to be set to a stable and valid logic level.

Klaus

 

[H2M]

Thanks for your reply Klaus.
My board is a prototype board and maybe i have to replace some ICs many times. I wanna tied unused pins to GND or VCC to make them tight. Because my PCB's pad don't destroy by replacing and soldering. So i wanna know what should i have done with not connected pins and unused pins? can i tied all of them to GND? W5500 have many NC pins: 6 pins are internally pull down and 2 pins are no internal electrical connection.Can i tied to GND all not connected pins in W5500 . My microcontroller is STM32f407 and i have many unused pins. can i set them as inputs and tied all of them to GND?
Thanks

 

[barry]

As Klaus said, you have to read the data sheet. Sometimes the manufacturer wants you to leave NC pins unconnected; arbitrarily pulling them to ground may be a bad thing. Tying NC pins to ground will make unsoldering the part harder, not easier.