19-0147; Rev. 3; 4/00
Microprocessor and Nonvolatile
Memory Supervisory Circuits
General Description
Features
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:
ꢀ Manual-Reset Input
ꢀ 200ms Power-OK/Reset Time Delay
ꢀ Independent Watchdog Timer—Preset or Adjustable
ꢀ On-Board Gating of Chip-Enable Signals
ꢀ Memory Write-Cycle Completion
• µP reset: Assertion of RESET and RESET outputs during
power-up, power-down, and brownout conditions.
RESET is guaranteed valid for VCC down to 1V.
ꢀ 10ns (max) Chip-Enable Gate Propagation Delay
ꢀ Voltage Monitor for Overvoltage Warning
• Manual-reset input.
• Two-stage power-fail warning: A separate low-line
comparator compares VCC to a preset threshold
120mV above the reset threshold; the low-line and
reset thresholds can be programmed externally.
ꢀ
2% Reset and Low-Line Threshold Accuracy
(MAX820, external programming mode)
Ordering Information
• Watchdog fault output: Assertion of WDO if the watchdog
input is not toggled within a preset timeout
period.
PART**
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*
MAX792_CPE
MAX792_CSE
MAX792_C/D
• Pulsed watchdog output: Advance warning of
impending WDO assertion from watchdog timeout that
causes hardware shutdown.
Ordering Information continued at end of data sheet.
* Dice are tested at T = +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.
• Write protection of CMOS RAM, EEPROM, or other
memory devices.
A
The MAX792 and MAX820 are identical, except the
MAX820 guarantees higher low-line and reset threshold
accuracy ( 2ꢀ).
SUFFIX
RESET THRESHOLD (V)
Applications
Computers
Controllers
L
M
T
S
R
4.62
4.37
3.06
2.91
2.61
Intelligent Instruments
Critical µP Power Monitoring
Typical Operating Circuit
V
CC
0.1µF
3
V
V
CC
CC
13
14
CE OUT
4
5
RESET IN/INT
µP
RAM
MAX792
ADDRESS
DECODER
CE IN
LLIN/
A0-A15
REFOUT
6
OVO
LOW LINE
RESET
10
1
NMI
7
8
OVI
RESET
9
MR
SWT
GND
12
GND
________________________________________________________________ Maxim Integrated Products
1
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