C8051F330 controlling power sequencing app note(PDF!) from Silicon Labs.
An increasing number of devices such as FPGAs, DSPs, RISC-CPUs, and communications ICs operate at two or more supply voltages. The core logic commonly operates from 1.3 to 2.5 V in order to save power while the I/O supply operates from 3.3 to 5 V to interface with other devices.
A common requirement for these ICs is that supply rails should track while ramping and stabilize at their target voltages 100 ms or more before the device is brought out of reset. Also, these devices often require large decoupling capacitors. Controlling in-rush current by limiting the slew rate on power up can prevent damage to the decoupling capacitors.
Many systems with multiple supplies require system health monitoring and protection. The health monitor checks for overvoltage, undervoltage, or overcurrent on any of the supply rails. It provides protection by putting the system into reset and shutting down all supply rails if abnormal conditions are detected on any of the supply rails.
The C8051F330 can provide low-cost power sequencing and supervision in systems with up to three power supply rails. During power ramp up, it controls in-rush current by limiting the output slew rate and performs real-time tracking to minimize the voltage difference between supplyrails. Once ramping is complete, it monitors the outputs and shuts down all supply rails if an over-voltage, under-voltage, over-current, or single-rail failure condition is detected.