Microprocessor and Non-Volatile

Memory Supervisory Circuits

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Maxim Integrated Products

1

19-0147; Rev. 2; 6/98

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 dur-

ing power-up, power-down, and brownout condi-

2) Manual-reset input.

3) Two-stage power-fail warning: A separate low-line

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%).

Applications

Computers

Controllers

Intelligent Instruments

Critical µP Power Monitoring

Features

o Manual-Reset Input

o 200ms Power-OK / Reset Time Delay

o Independent Watchdog Timer—Preset or Adjustable

o On-Board Gating of Chip-Enable Signals

o Memory Write-Cycle Completion

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

o Voltage Monitor for Overvoltage Warning

o ±2% Reset and Low-Line Threshold Accuracy

(MAX820, external programming mode)

Ordering Information continued at end of data sheet.

**These parts offer a choice of five different reset threshold volt-

ages. Select the letter corresponding to the desired nominal

reset threshold voltage and insert it into the blank to complete the

part number.

MAX792

4

5

7

8

9

1

10

6

14

ADDRESS

DECODER

RESET IN/INT

LLIN/

REFOUT

OVI

SWT

3

GND

12

MR

RESET

LOW LINE

OVO

CE IN

CE OUT

0.1µF

RAM

A0-A15

GND

NMI

RESET

µP

13

Typical Operating Circuit

PART**

TEMP. RANGE

PIN-PACKAGE

MAX792_CPE

0°C to +70°C

16 Plastic DIP

MAX792_CSE

0°C to +70°C

16 Narrow SO

MAX792_C/D

0°C to +70°C

Dice*

SUFFIX

RESET THRESHOLD (V)

4.62

4.37

3.06

2.91

2.61

L

M

T

S

R

For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800.

For small orders, phone 1-800-835-8769.

Ordering Information