Power on Sequence

Created:7/12/2021Last Updated:7/12/2021

Power on sequence generally refers to a series of power supply rail turn-on times for a processor in order to ensure proper start-up and functional integrity of the processor or system on chip.

The reason for having a power-on sequence is that a processor chip contains many parts, such as the core, memory, clocks, and input and output transceivers. A core needs to come before input and output transceivers are powered, or else the transceiver output driver input voltage is unknown. This created an unknown state at the I/O output driver level. Hence, the known good state of each component of the processor needs to be ensured before the next stage of events can happen. For example, cores, clocks, and internal memories should be powered up before interfacing with system memory and persistent storage such as DRAMS and NAND Flash.

Ways to design power in sequence

Things to watch out for