Hi,I am using STM32L431CCT6 MCU in my design. I have space limitation on my PCB and did not place pull up/pull down resistors on unused pins. Is there a problem? What is the recommendation here?

[SG.13]

 My boot up time is about 30mSec. I would like to know how the pins behave during boot up. Does it behave as high impedance i/p or as o/p sourcing/sinking current? In my design I am shorting two IO pins. Is there a chance during boot up one can sourcing o/p and other can be sinking o/p?

[Jack Peacock_2]

At reset GPIO pins are configured for analog, high impedance input. If a GPIO controls a critical circuit at power up you'll need to have an external PU or PD to provide a stable power on reset condition.

The internal GPIOs can be set to keep a PU/PD active in STANDBY, but this doesn't apply to a cold reset. Internal PU/PD requires more power from a battery than a high value external resistor if you are running from batteries.

Jack Peacock