PMBus stands for
Power Management Bus, an abbreviation for a open-standards
protocol established over the last few years for
digital power managment in systems. The protocol uses the
I2C data bus (created by
Philips in the '80's for inter-chip communications).
Digital power management involves incorporating management and monitoring logic in all the power supplies on the circuit board to enable each to be individually monitored for temperature, output voltage & current, and be programmed for not only voltage and current but also turn-on sequence with the other supplies on the board and how fast and steep the "slope" of the power-up curve should be.