MAX791

19-0075; Rev. 5; 7/95 Microprocessor Supervisory Circuit _____________________General Description The MAX791 microprocessor (µP) supervisory circuit reduces the complexity and number of components needed to monitor power-supply and battery-control functions in µP systems. The 50µA supply current makes the MAX791 ideal for use in portable equipment, while the 6ns chip-enable propagation delay and 250mA output capability (25mA in battery-backup mode) make it suitable for larger, higher-performance equipment. The MAX791 comes in 16-pin DIP and narrow SO packages and provides the following functions: – — — — — – 1) µP reset—RESET output is asserted during power-up, power-down, and brownout conditions, and is guaranteed to be in the correct state for VCC down to 1V, even with no battery in the circuit. 2) Manual-reset input. 3) A 1.25V threshold detector provides for power-fail warning and low-battery detection, or monitors a power supply other than +5V. 4) Two-stage power-fail warning—a separate low-line comparator compares V CC to a threshold 150mV above the reset threshold. 5) Backup-battery switchover for CMOS RAM, real-time clocks, µPs, or other low-power logic. 6) Software monitoring of backup-battery voltage. 7) A watchdog-fault output is asserted if the watchdog input has not been toggled within either a preset or an adjustable timeout period. 8) Write protection of CMOS RAM or EEPROM. 9) Pulsed watchdog –— — – output, to give advance warning of impending WDO assertion ca...