Let your application determine the right microprocessor supervisor: There are a series of steps to follow when implementing a processor-supervisor circuit. Follow them, and you'll be sure to make the right choice

摘要

Choosing an appropriate microprocessor-supervisor IC from among the hundreds of models available can be a quite a task. The selection process consists of the following five steps: ·Selecting the reset-threshold voltage. ·Selecting the reset time. ·Selecting output characteristics. ·Selecting additional features-manual reset, watchdog, power fail, battery management, mul tiple voltages, power sequencing, package, and supply current. ·Refining your selection-price and preferred parts. A supervisor IC keeps the processor in reset mode until the power-supply voltages and clock signals settle down. When you turn on a piece of electronic equipment, the filter capacitors begin to charge, causing the supply voltage to begin ramping up. A phase-locked loop (PLL) (if used to generate the clock signal) starts searching for a phase lock. Because power-supply voltages and clock frequencies are out of spec during this time, digital circuitry may operate erratically. Circuits may turn on at the wrong time, memories may be overwritten, equipment may be damaged, or the system may assume an unrecoverable state.