19-0147; Rev. 3; 4/00
Microprocessor and Nonvolatile
Memory Supervisory Circuits
General Description
The MAX792/MAX820 microprocessor (µP) supervisory
circuits provide the most functions for power-supply
and watchdog monitoring in systems without battery
backup. Built-in features include the following:
• µP reset: Assertion of RESET and
RESET
outputs during
power-up, power-down, and brownout conditions.
RESET
is guaranteed valid for V
CC
down to 1V.
• Manual-reset input.
• Two-stage power-fail warning: A separate low-line
comparator compares V
CC
to a preset threshold
120mV above the reset threshold; the low-line and
reset thresholds can be programmed externally.
• Watchdog fault output: Assertion of
WDO
if the watchdog
input is not toggled within a preset timeout
period.
• Pulsed watchdog output: Advance warning of
impending
WDO
assertion from watchdog timeout that
causes hardware shutdown.
• Write protection of CMOS RAM, EEPROM, or other
memory devices.
The MAX792 and MAX820 are identical, except the
MAX820 guarantees higher low-line and reset threshold
accuracy (±2%).
o
Manual-Reset Input
o
200ms Power-OK / Reset Time Delay
o
Independent Watchdog Timer—Preset or Adjustable
o
On-Board Gating of Chip-Enable Signals
o
Memory Write-Cycle Completion
o
10ns (max) Chip-Enable Gate Propagation Delay
o
Voltage Monitor for Overvoltage Warning
o
±2% Reset and Low-Line Threshold Accuracy
(MAX820, external programming mode)
Features
MAX792/MAX820
Ordering Information
PART**
MAX792_CPE
MAX792_CSE
MAX792_C/D
TEMP. RANGE
0°C to +70°C
0°C to +70°C
0°C to +70°C
PIN-PACKAGE
16 Plastic DIP
16 Narrow SO
Dice*
Ordering Information continued at end of data sheet.
* Dice are tested at T
A
= +25°C, DC parameters only.
**These parts offer a choice of five different reset threshold volt-
ages. Select the letter corresponding to the desired nominal
reset threshold voltage and insert it into the blank to complete the
part number.
SUFFIX
L
M
T
S
R
RESET THRESHOLD (V)
4.62
4.37
3.06
2.91
2.61
Applications
Computers
Controllers
Intelligent Instruments
Critical µP Power Monitoring
Typical Operating Circuit
3
V
CC
4
CE OUT
RESET IN/INT
0.1µF
13
V
CC
V
CC
µP
MAX792
5
LLIN/
REFOUT
CE IN
OVO
LOW LINE
7
8
OVI
SWT
GND
12
RESET
MR
14
6
10
1
9
GND
NMI
RESET
ADDRESS
DECODER
RAM
A0-A15
________________________________________________________________
Maxim Integrated Products
1
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