19-0075; Rev. 5; 7/95
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 and narrow SO pack-
ages and provides the following functions:
–——
— —–
1) µP reset—RESET output is asserted during power-up,
power-down, and brownout conditions, and is guaran-
teed to be in the correct state for V
CC
down to 1V,
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
comparator compares V
CC
to a threshold 150mV
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 WDO assertion caused by watchdog timeout.
____________________________Features
o
o
o
o
o
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 V
CC
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 RESET Valid to V
CC
= 1V
MAX791
o
o
o
o
o
‰
‰
______________Ordering Information
PART
MAX791CPE
MAX791CSE
MAX791C/D
MAX791EPE
MAX791ESE
MAX791EJE
MAX791MJE
TEMP. RANGE
0°C to +70°C
0°C to +70°C
0°C to +70°C
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
-55°C to +125°C
PIN-PACKAGE
16 Plastic DIP
16 Narrow SO
Dice*
16 Plastic DIP
16 Narrow SO
16 CERDIP
16 CERDIP
* Dice are specified at T
A
= +25°C.
________________________Applications
Computers
Critical µP Power Monitoring
Controllers
Intelligent Instruments
Portable/Battery-Powered Equipment
__________Typical Operating Circuit
+5V
0.1µF
0.1µF
CMOS
RAM
__________________Pin Configuration
TOP VIEW
VBATT 1
V
OUT
2
V
CC
3
GND 4
BATT ON 5
PFO 6
PFI 7
SWT 8
16 WDPO
15 RESET
14 WDO
+12V
0.47F*
OTHER SYSTEM
RESET SOURCES
V
CC
VBATT
BATT
ON
SWT
V
OUT
CE OUT
MR
CE IN
PFI
MAX791
+12V SUPPLY
FAILURE
WDI
PFO
GND
LOWLINE
RESET
WDO
*MaxCap™
ADDRESS
DECODE
A0–A15
µP
I/O
NMI
RESET
INT
MAX791
13 CE IN
12 CE OUT
11 WDI
10 LOWLINE
9
MR
DIP/SO
™
MaxCap is a registered trademark of The Carborundum Corp.
™
SuperCap is a registered trademark of Baknor Industries.
________________________________________________________________
Maxim Integrated Products
1
Call toll free 1-800-998-8800 for free samples or literature.
MAXIM [ MAXIM INTEGRATED PRODUCTS ]
