Microprocessor Supervisory Circuit

________________________________________________________________

Maxim Integrated Products

1

Call toll free 1-800-998-8800 for free samples or literature.

19-0075; Rev. 5; 7/95

_____________________

General Description

The MAX791 microprocessor (µP) supervisory circuit

reduces the complexity and number of components need-

ed 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 capa-

bility (25mA in battery-backup mode) make it suitable for

larger, higher-performance equipment.

The MAX791 comes in 16-pin DIP and narrow SO pack-

ages and provides the following functions:

1) µP reset—

–

R

—

E

—

S

—

E

—

T

–

output is asserted during power-up,

power-down, and brownout conditions, and is guaran-

even with no battery in the circuit.

2) Manual-reset input.

3) A 1.25V threshold detector provides for power-fail

warning and low-battery detection, or monitors a

power supply other than +5V.

4) Two-stage power-fail warning—a separate low-line

above the reset threshold.

5) Backup-battery switchover for CMOS RAM, real-time

clocks, µPs, or other low-power logic.

6) Software monitoring of backup-battery voltage.

7) A watchdog-fault output is asserted if the watchdog

input has not been toggled within either a preset or

an adjustable timeout period.

8) Write protection of CMOS RAM or EEPROM.

9) Pulsed watchdog output, to give advance warning of

impending

–

W

—

D

—

O

–

assertion caused by watchdog timeout.

________________________Applications

Computers

Critical µP Power Monitoring

Controllers

Intelligent Instruments

Portable/Battery-Powered Equipment

____________________________Features

o Precision 4.65V Voltage Monitoring

o 200ms Power-OK / Reset Time Delay

o Independent Watchdog Timer—Preset or Adjustable

o 1µA Standby Current

o Power Switching

25mA Output in Battery-Backup Mode

o On-Board Gating of Chip-Enable Signals

Memory Write-Cycle Completion

6ns CE Gate Propagation Delay

o MaxCap

‰ or SuperCap‰ Compatible

o Voltage Monitor for Power-Fail or Low-Battery Warning

o Backup-Battery Monitor

o Guaranteed

–

R

—

E

—

S

—

E

—

T

–

______________Ordering Information

16

15

14

13

12

11

10

9

1

2

3

4

5

6

7

8

WDPO

RESET

WDO

CE IN

GND

VBATT

TOP VIEW

MAX791

CE OUT

WDI

LOWLINE

MR

SWT

PFI

PFO

BATT ON

DIP/SO

CMOS

RAM

MAX791

RESET

LOWLINE

WDI

CE IN

CE OUT

+5V

OTHER SYSTEM

RESET SOURCES

+12V

VBATT

*MaxCap™

A0–A15

MR

+12V SUPPLY

FAILURE

BATT

ON

SWT

ADDRESS

DECODE

0.1

µF

0.1

µF

0.47F*

PFI

PFO

GND

I/O

µP

NMI

INT

RESET

WDO

__________________Pin Configuration

__________Typical Operating Circuit

PART

TEMP. RANGE

PIN-PACKAGE

MAX791CPE

0°C to +70°C

16 Plastic DIP

MAX791CSE

0°C to +70°C

16 Narrow SO

MAX791C/D

0°C to +70°C

Dice*

MAX791EPE

-40°C to +85°C

16 Plastic DIP

MAX791ESE

-40°C to +85°C

16 Narrow SO

MAX791EJE

-40°C to +85°C

16 CERDIP

MAX791MJE

-55°C to +125°C

16 CERDIP

™MaxCap is a registered trademark of The Carborundum Corp. ™SuperCap is a registered trademark of Baknor Industries.