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-bar 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 VCC 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-bar assertion caused by watchdog timeout.

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