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:

• 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.

• 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 WDO if the watchdog

   input is not toggled within a preset timeout

   period.

• Pulsed watchdog output: Advance warning of

   impending 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%).

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