3V 5V Buck Regulator IC Datasheet

Step down or switch-mode power supply (SMPS) controller generates logic-supply voltages in battery powered systems.

This IC generates 3v and 5v in laptop motherboard, If you have a short or damage step down IC, your laptop will not power on at all. 5v is mostly used for laptop peripherals, whereas 3v is used for BIOS chip, Super IO (SIO), Power Button, LID switch and many more.