MAX791 Datasheet, PDF (1/20 Pages) Maxim Integrated Products – Microprocessor Supervisory Circuit

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—–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.
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 VCC 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)
iPmuplseenddiwngat–Wc—hD—dOo–gasosuetrptiuotn,
to give
caused
advance warning of
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
250mA Output in VCC Mode
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–} Valid to VCC = 1V
______________Ordering Information
PART
TEMP. RANGE
MAX791CPE
0°C to +70°C
MAX791CSE
0°C to +70°C
MAX791C/D
0°C to +70°C
MAX791EPE
-40°C to +85°C
MAX791ESE
-40°C to +85°C
MAX791EJE
-40°C to +85°C
MAX791MJE
-55°C to +125°C
* Dice are specified at T_A = +25°C.
PIN-PACKAGE
16 Plastic DIP
16 Narrow SO
Dice*
16 Plastic DIP
16 Narrow SO
16 CERDIP
16 CERDIP
__________Typical Operating Circuit
+5V
0.1µF
0.1µF
CMOS
RAM
__________________Pin Configuration
TOP VIEW
VBATT ₁
VOUT 2
VCC ₃
GND ₄
BATT ON 5
PFO 6
PFI ₇
SWT ₈
MAX791
DIP/SO
16 ^WDPO
15 ^RESET
14 ^WDO
13 CE IN
12 CE OUT
11 WDI
10 LOWLINE
9 MR
0.47F*
OTHER SYSTEM
RESET SOURCES
VCC BATT SWT
VBATT ^{ON V}OUT
CE OUT
MR
+12V
CE IN
PFI ^MAX791
+12V SUPPLY
PFO
FAILURE
GND
WDI
LOWLINE
RESET
WDO
ADDRESS
DECODE
*MaxCap_™
A0–A15
µP
I/O
NMI
RESET
INT
™_{MaxCap is a registered trademark of The Carborundum Corp.} ™_{SuperCap is a registered trademark of Baknor Industries.}
________________________________________________________________ Maxim Integrated Products 1
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