19-0075; Rev. 7; 11/05
Microprocessor Supervisory Circuit
Applications
Computers
Controllers
Portable/BatteryPowered Equipment
Critical µP Power Monitoring
Intelligent Instruments
Features
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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 RESET Valid to VCC = 1V
Ordering Information
PART
TEMP RANGE
PIN-PACKAGE
MAX791CPE
0°C to +70°C
16 Plastic DIP
MAX791CSE
MAX791C/D
MAX791CUE
MAX791EPE
0°C to +70°C
0°C to +70°C
0°C to +70°C
-40°C to +85°C
16 Narrow SO
Dice*
16 TSSOP
16 Plastic DIP
MAX791ESE
MAX791EJE
MAX791EUE
MAX791MJE
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
-55°C to +125°C
16 Narrow SO
16 CERDIP
16 TSSOP
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
Pin Configuration
+5V
CMOS
RAM
0.1µF
0.1µF
TOP VIEW
VBATT 1
16 WDPO
VOUT 2
15 RESET
VCC 3
0.47F*
OTHER SYSTEM
RESET SOURCES
VCC
VBATT
14 WDO
GND 4
MAX791
BATT ON 5
CE OUT
13 CE IN
PFI MAX791
+12V SUPPLY
10 LOWLINE
SWT 8
9
CE IN
+12V
11 WDI
PFI 7
SWT
VOUT
MR
12 CE OUT
PFO 6
BATT
ON
FAILURE
MR
WDI
PFO
GND
LOWLINE
RESET
WDO
DIP/SO/TSSOP
ADDRESS
DECODE
A0–A15
µP
I/O
NMI
RESET
INT
*MaxCap
MaxCap is a registered trademark of Cesiwid Inc. SuperCap is a registered trademark of Baknor Industries.
________________________________________________________________ Maxim Integrated Products
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.
1
MAX791
General Description
The MAX791 microprocessor (µP) supervisory circuit
reduces the complexity and number of components needed 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 capability (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. RESET output is asserted during power-up,
power-down, and brownout conditions, and is guaranteed 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 V CC 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.
• Pulsed watchdog output to give advance warning of
–— –
—
impending WDO assertion caused by watchdog timeout.