General Description

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:
1) µP reset: Assertion of RESET and RESET outputs during power-up, power-down,
and brownout conditions. RESET is guaranteed valid for VCC down to 1V.
2) Manual-reset input.
3) 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.
4) Watchdog fault output: Assertion of WDO if the watch
dog input is not toggled within a preset timeout
period.
5) Pulsed watchdog output: Advance warning of
impending WDO assertion from watchdog timeout
that causes hardware shutdown.
6) 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%).

Features

♦ 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)

Applications

Computers
Controllers
Intelligent Instruments
Critical µP Power Monitoring