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:
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.
Manual-reset input.
A 1.25V threshold detector provides for power-fail warning and low-battery detection, or monitors a power supply other than +5V.
Two-stage power-fail warning-a separate low-line comparator compares VCC to a threshold 150mV above the reset threshold.
Backup-battery switchover for CMOS RAM, real-time clocks, µPs, or other low-power logic.
Software monitoring of backup-battery voltage.
A watchdog-fault output is asserted if the watchdog input has not been toggled within either a preset or an adjustable timeout period.
Write protection of CMOS RAM or EEPROM.
Pulsed watchdog output, to give advance warning of impending WDO-bar assertion caused by watchdog timeout.
Key Features
Applications/Uses
Precision 4.65V Voltage Monitoring
200ms Power-OK/Reset Time Delay
Independent Watchdog Timer-Preset or Adjustable
1µA Standby Current
Power Switching
250mA Output in VCC Mode
25mA Output in Battery-Backup Mode
On-Board Gating of Chip-Enable Signals
Memory Write-Cycle Completion
6ns CE Gate Propagation Delay
MaxCap™ or SuperCap™ Compatible
Voltage Monitor for Power-Fail or Low-Battery Warning
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