Microprocessor and Nonvolatile Memory Supervisory Circuits

The MAX792/MAX820 microprocessor (µP) supervisory circuits provide the most functions for power-supply and watchdog monitoring in systems without battery backup. Built-in features include the following:

* µP reset: Assertion of RESET and active-low RESET outputs during power-up, power-down, and brownout conditions. Active-low RESET is guaranteed valid for VCC down to 1V.

* Manual-reset input.

* Two-stage power-fail warning: A separate low-line comparator compares VCC to a preset threshold 120mV above the reset threshold; the low-line and reset thresholds can be programmed externally.

* Watchdog fault output: Assertion of active-low WDO if the watchdog input is not toggled within a preset timeout period.

* Pulsed watchdog output: Advance warning of impending active-low WDO assertion from watchdog timeout that causes hardware shutdown.

* Write protection of CMOS RAM, EEPROM, or other memory devices.

The MAX792 and MAX820 are identical, except the MAX820 guarantees higher low-line and reset threshold accuracy (±2%).Applications

* Computers: Desktop, Workstation, Server * Controllers * Critical µP Monitoring * Intelligent Instruments

* Manual-Reset Input

* 200ms Power OK/Reset Time Delay

* Independent Watchdog Timer-Preset or Adjustable

* On-Board Gating of Chip-Enable Signals

* Memory Write-Cycle Completion

* 10ns (max) Chip-Enable Gate Propagation Delay

* Voltage Monitor for Overvoltage Warning

* ±2% Reset and Low-Line Threshold Accuracy (MAX820, external programming mode)