LPC55S28 - connecting unused pins

[ranjeetm]

Hi - We are looking to use the LPC55S28 device and do not intend using external Crystal or the USB interface. Is there a Hardware Checklist available which provides guidance as to how to connect the Unused pins.

thanks

regards, 

[Omar_Anguiano]

Hello Ranjeet Malhotra

Under chapter 6.1.1 you can find a table that shows how to terminate pins that are not used in the application https://www.nxp.com/docs/en/data-sheet/LPC55S2X-LPC552X.pdf

Let me know if this is helpful, if you have more questions do not hesitate to ask me.

Best regards,

Omar

[ranjeetm]

Thanks - that was very helpful. A follow up question - can any of the GPIO lines of the Microcontroller be connected to a signal when the device itself isn't powered? We are specifically looking to connect one of the Flexcom's to another system using I2C and do not have any control over power sequence. There will be instances when the other system may get powered first and provide signals on the I2C lines while the Microcontroller is not powered. Will the I/O pins get damaged? Do we need to isolate the bus?

regards, Ranjeet

[Omar_Anguiano]

Hello Ranjeet Malhotra

Analog pins are more susceptible to damage in this circumstances, digital pins have some protection circuitry, however, I suggest to isolate the pins if the pins will be receiving signals when the MCU is off in order to avoid any damage.

Let me know if this is helpful, if you have more questions do not hesitate to ask me.

Best regards,

Omar