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MAX791E

Microprocessor Supervisory Circuit

Maxim Integrated 

19-0075; Rev. 7; 11/05

Microprocessor Supervisory Circuit

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, TSSOP, and narrow SO

packages and provides the following functions:

• µP reset. –R—E—S—E—T– output is asserted during power-up,

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

teed to be in the correct state for VCC down to 1V,

even with no battery in the circuit.

• Manual-reset input.

• A 1.25V threshold detector provides for power-fail

warning and low-battery detection, or monitors a

power supply other than +5V.

• Two-stage power-fail warning. A separate low-line

comparator compares VCC to a threshold 150mV

above the reset threshold.

• Backup-battery switchover for CMOS RAM, real-time

clocks, µPs, or other low-power logic.

• Software monitoring of backup-battery voltage.

• A watchdog-fault output is asserted if the watchdog

input has not been toggled within either a preset or

an adjustable timeout period.

• Write protection of CMOS RAM or EEPROM.

•

Pimuplseenddiwngat–Wc—hD—dOo–gasosuetrptiount

to give

caused

advance warning of

by watchdog timeout.

Applications

Computers

Controllers

Portable/Battery-

Powered Equipment

Critical µP Power Monitoring

Intelligent Instruments

Pin Configuration

TOP VIEW

VBATT 1

VOUT 2

VCC 3

GND 4

BATT ON 5

PFO 6

PFI 7

SWT 8

MAX791

16 WDPO

15 RESET

14 WDO

13 CE IN

12 CE OUT

11 WDI

10 LOWLINE

9 MR

DIP/SO/TSSOP

Features

♦ Precision 4.65V Voltage Monitoring

♦ 200ms Power-OK / Reset Time Delay

♦ Independent Watchdog Timer—Preset or Adjustable

♦ 1µA Standby Current

♦ Power Switching

250mA Output in VCC Mode

25mA Output in Battery-Backup Mode

♦ On-Board Gating of Chip-Enable Signals

Memory Write-Cycle Completion

6ns CE Gate Propagation Delay

♦ MaxCap or SuperCap Compatible

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

♦ Backup-Battery Monitor

♦ Guaranteed –R—E—S—E—T– Valid to VCC = 1V

Ordering Information

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*

MAX791CUE

0°C to +70°C

16 TSSOP

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

MAX791EUE

-40°C to +85°C

16 TSSOP

MAX791MJE

-55°C to +125°C

16 CERDIP

* Dice are specified at TA = +25°C.

Devices in PDIP, SO and TSSOP packages are available in both

leaded and lead-free packaging. Specify lead free by adding

the + symbol at the end of the part number when ordering.

Lead free not available for CERDIP package.

Typical Operating Circuit

+5V

0.1µF

0.1µF

CMOS

RAM

0.47F*

OTHER SYSTEM

RESET SOURCES

VCC BATT SWT

VBATT ON VOUT

CE OUT

MR

+12V

CE IN

PFI MAX791

+12V SUPPLY

PFO

FAILURE

GND

*MaxCap

WDI

LOWLINE

RESET

WDO

ADDRESS

DECODE

A0–A15

µP

I/O

NMI

RESET

INT

MaxCap is a registered trademark of Cesiwid Inc. SuperCap is a registered trademark of Baknor Industries.

________________________________________________________________ Maxim Integrated Products 1

For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at

1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.

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