Highly integrated system chips, which combine multiple digital and analog functions into a single package, often require multiple power supplies. Usually the microprocessor’s input/output (I/O) and core voltages are two separate and independent power requirements. A typical contemporary microprocessor’s I/O section usually operates at 3.3 V or 2.5 V, but the core sections operate at 1.8 V, 1.5 V, 1.3 V or lower. Improper supply sequencing
can result in device latchup, incorrect device initiation, or degradation of long?term reliability. Considering these issues, it’s important to consider the control of the supply?voltage sequencing to guarantee proper system operation. For example, DSPs and some other multi?voltage processors require their I/O voltage to be present before applying the core voltage.