Think of I2C as a postal service—reliable, cheap, and good for most non-urgent deliveries. Think of SPMI as an armored courier with built-in checksums and a panic button. You don’t need an armored courier to deliver a temperature reading, but you absolutely need one to adjust the core voltage of a $50 CPU.
Modern CPUs change voltage hundreds of times per second to save power. I2C’s handshaking and start/stop conditions introduce delays. SPMI uses a streamlined "register write" with less overhead, allowing faster voltage transitions. spmi vs i2c
A single bit flip on an I2C bus could tell your PMIC to raise the core voltage to 1.8V instead of 1.1V. That can fry the CPU. SPMI includes a mandatory 8-bit CRC on every transaction, guaranteeing data integrity. Think of I2C as a postal service—reliable, cheap,