19-0147; Rev. 4; 11/05
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%).
Features
♦
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
10ns (max) Chip-Enable Gate Propagation Delay
Voltage Monitor for Overvoltage Warning
±2% Reset and Low-Line Threshold Accuracy
(MAX820, external programming mode)
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 voltages.
Select the letter corresponding to the desired nominal reset threshold
voltage and insert it into the blank to complete the part number.
Devices in PDIP, SO and µMAX packages are available in both lead-
ed and lead-free packaging. Specify lead free by adding the + sym-
bol at the end of the part number when ordering. Lead free not avail-
able for CERDIP package.
Applications
Computers
Controllers
Intelligent Instruments
Critical µP Power Monitoring
SUFFIX
L
M
T
S
R
RESET THRESHOLD (V)
4.62
4.37
3.06
2.91
2.61
Typical Operating Circuit
3
V
CC
4
CE OUT
RESET IN/INT
13
0.1µF
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
For free samples and the latest literature, visit www.maxim-ic.com or phone 1-800-998-8800.
For small orders, phone 1-800-835-8769.
Microprocessor and Nonvolatile
Memory Supervisory Circuits
MAX792/MAX820
ABSOLUTE MAXIMUM RATINGS
Input Voltage (with respect to GND)
V
CC
.......................................................................-0.3V to +6V
All Other Inputs.......................................-0.3V to (V
CC
+ 0.3V)
Input Current
GND ................................................................................25mA
All Other Outputs ............................................................25mA
Continuous Power Dissipation (T
A
= +70°C)
Plastic DIP (derate 10.53mW/°C above +70°C) ..........842mW
Narrow SO (derate 9.52mW/°C above +70°C) ............762mW
CERDIP (derate 10.00mW/°C above +70°C) ...............800mW
Operating Temperature Ranges:
MAX792_C_ _/MAX820_C_ _ ...............................0°C to +70°C
MAX792_E_ _/MAX820_E_ _.............................-40°C to +85°C
MAX792_MJE_ _/MAX820_MJE_ _ .................-55°C to +125°C
Storage Temperature Range .............................-65°C to +160°C
Lead Temperature (soldering, 10s) .................................+300°C
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
ELECTRICAL CHARACTERISTICS
(V
CC
= 2.75V to 5.5V, T
A
= T
MIN
to T
MAX
, unless otherwise noted.)
PARAMETER
Operating Voltage Range
(Note 1)
Supply Current
RESET COMPARATOR
MAX792L, MAX820L
MAX792M, MAX820M
MAX792R, MAX820R
MAX792S, MAX820S
Reset Threshold Voltage—
Internal Threshold Mode
(V
TH
)
MAX792T, MAX820T
MAX820L, T
A
= +25°C, V
CC
falling
MAX820M, T
A
= +25°C, V
CC
falling
MAX820R, T
A
= +25°C, V
CC
falling
MAX820S, T
A
= +25°C, V
CC
falling
MAX820T, T
A
= +25°C, V
CC
falling
MAX792, V
CC
= 5V or V
CC
= 3V
MAX820, V
CC
= 5V or V
CC
= 3V
Internal threshold mode
±0.01
V
CC
falling
V
CC
rising
I
SINK
= 50µA, V
CC
= 1V, V
CC
falling
I
SINK
= 1.6mA
I
SOURCE
= 1mA
I
SOURCE
= 100µA
I
SINK
= 1.6mA
I
SOURCE
= 1mA
I
SOURCE
= 100µA
4.50
4.25
2.55
2.85
3.00
4.55
4.30
2.55
2.85
3.00
1.25
1.274
4.62
4.37
2.61
2.91
3.06
4.75
4.50
2.70
3.00
3.15
4.70
4.45
2.66
2.96
3.11
1.35
1.326
60
±25
V
CONDITIONS
MIN
2.75
70
150
TYP
MAX
UNITS
V
µA
Reset Threshold Voltage
External Threshold Mode (V
TH
)
RESET IN/INT Mode Threshold
(Note 2)
RESET IN/INT Leakage Current
Reset Threshold Hysteresis
Reset Comparator Delay
Reset Active Timeout Period
1.30
1.30
V
mV
nA
V
µs
ms
140
RESET
Output Voltage
0.016 x V
TH
70
200
280
0.01
0.3
0.1
0.4
V
CC
- 1
V
CC
- 0.5
0.1
V
CC
- 1
V
CC
- 0.5
0.4
V
RESET Output Voltage
V
2
_______________________________________________________________________________________
Microprocessor and Nonvolatile
Memory Supervisory Circuits
ELECTRICAL CHARACTERISTICS (continued)
(V
CC
= 2.75V to 5.5V, T
A
= T
MIN
to T
MAX
, unless otherwise noted.)
PARAMETER
LOW-LINE COMPARATOR
Low-Line Threshold Voltage
(Internal Threshold Mode)—V
TH
Low-Line Threshold Voltage
(External Programming Mode)
Low-Line Hysteresis
(Internal Threshold Mode)
LLIN/REFOUT Leakage Current
External Programming Mode
Low-Line Comparator Delay
LOWLINE
Voltage
LOWLINE
Short-Circuit Current
WATCHDOG FUNCTION
SWT connected to V
CC
, V
CC
= 5V
SWT connected to V
CC
, V
CC
= 3V
Watchdog Timeout Period
4.7nF capacitor connected from SWT to GND,
V
CC
= 3V
4.7nF capacitor connected from SWT to GND,
V
CC
= 5V
Watchdog Input Pulse Width
V
CC
= 5V
V
CC
= 3V
I
SINK
= 50µA, V
CC
= 1V, V
CC
falling
I
SINK
= 1.6mA
I
SOURCE
= 1mA
I
SOURCE
= 100µA
V
IL
= 0V, V
IH
= V
CC
100
300
0.01
0.1
V
CC
- 1
V
CC
- 0.5
70
0.5
I
SINK
= 50µA, V
CC
= 1V, V
CC
falling
I
SINK
= 1.6mA
I
SOURCE
= 1mA
I
SOURCE
= 100µA
V
IH
V
CC
= 4.25V
V
IL
V
IH
V
CC
= 2.55V
V
IL
1.7
0.01
0.1
V
CC
- 1
V
CC
- 0.5
0.75 x V
CC
0.8
0.9 x V
CC
0.2
±1
6.0
0.3
0.4
0.30
0.4
1.00
1.00
1.60
1.60
70
ms
100
ns
2.25
2.25
sec
V
CC
falling
I
SINK
= 3.2mA
ISOURCE
= 1µA
MAX792/MAX820
CONDITIONS
MAX792/MAX820L/M
MAX792/MAX820R/S/T
MAX792, V
CC
= 5V OR V
CC
= 3V
MAX820, V
CC
= 5V OR V
CC
= 3V
MIN
50
40
1.25
1.274
TYP
120
100
1.30
1.30
20
±0.01
450
MAX
210
210
1.35
1.326
UNITS
mV
V
mV
±25
nA
µs
0.4
V
CC
- 1
10
50
V
µA
Output source current, V
CC
= 5.5V
WDO
Output Voltage
V
WDPO
to
WDO
Delay
WDPO
Duration
ns
ms
WDPO
Output Voltage
V
WDI Threshold Voltage
V
WDI Input Current
µA
_______________________________________________________________________________________
3
Microprocessor and Nonvolatile
Memory Supervisory Circuits
MAX792/MAX820
ELECTRICAL CHARACTERISTICS (continued)
(V
CC
= +2.75V to +5.5V, T
A
= T
MIN
to T
MAX
, unless otherwise noted.)
PARAMETER
OVERVOLTAGE COMPARATOR
OVI Input Threshold
OVI Leakage Current
OVO
Output Voltage
OVO
Short-Circuit Current
OVI to
OVO
Delay
CHIP-ENABLE GATING
V
CC
= 4.25V
CE
IN Threshold Voltage
V
CC
= 2.55V
CE
IN Leakage Current
CE
IN to
CE
OUT Resistance
CE
OUT Short-Circuit Current
Chip-Enable Propagation Delay
(Note 3)
Chip-Enable Output Voltage
High (Reset Active)
Reset Active to
CE
OUT High
MANUAL RESET
MR
Minimum Pulse Width
MR
to
RESET
Propagation Delay
MR
Threshold Range
MR
Pull-Up Current
MR
= 0V
V
CC
= 4.25V
to V
CC
= 5.5V
V
CC
= 2.5V
1.1
5
1
25
12
1.3
23
1.5
80
µs
µs
V
µA
Disabled mode
Enabled mode
Disabled mode,
CE
OUT
= 0V
50Ω source impedance driver,
C
LOAD
= 50pF
I
OUT
= -100µA
I
OUT
= 10µA
V
CC
falling
V
CC
= 5V
V
CC
= 3V
V
CC
= 5V
V
CC
= 3V
V
CC
= 5V
V
CC
= 3V
V
CC
- 1
V
CC
- 0.5
15
V
IH
V
IL
V
IH
V
IL
0.75 x V
CC
0.8
0.75 x V
CC
0.2
±0.005
75
150
0.5
0.05
0.2
6
8
±1
150
300
2.5
0.4
10
13
µA
Ω
mA
ns
V
µs
V
I
SINK
= 3.2mA
I
SOURCE
= 1µA
Output source current, V
CC
= 5.5V
V
OD
= 100mV, OVI rising
V
OD
= 100mV, OVI falling
V
CC
- 1
10
13
55
50
V
CC
= 5V or V
CC
= 3V
1.25
1.30
±0.01
1.35
±25
0.4
V
nA
V
µA
µs
CONDITIONS
MIN
TYP
MAX
UNITS
Note 1:
The minimum operating voltage is 2.75V; however, the MAX792R and MAX820R are guaranteed to operate down to their
preset reset thresholds.
Note 2:
Pulling RESET IN/INT below 60mV selects internal threshold mode and connects the internal voltage divider to the reset
and low-line comparators. External programming mode allows an external resistor divider to set the low-line and reset
thresholds (see Figure 4).
Note 3:
The Chip-Enable Propagation delay is measured from the 50% point at
CE
IN to the 50% point at
CE
OUT.
4
_______________________________________________________________________________________
Microprocessor and Nonvolatile
Memory Supervisory Circuits
MAX792/MAX820
__________________________________________Typical Operating Characteristics
(T
A
= +25°C, unless otherwise noted.)
SUPPLY CURRENT vs. TEMPERATURE
MAX792-1
OVERVOLTAGE COMPARATOR
PROPAGATION DELAY vs. TEMPERATURE
MAX792-2
RESET COMPARATOR
PROPAGATION DELAY vs. TEMPERATURE
MAX792-3
100
90
80
SUPPLY CURRENT (µA)
70
60
50
40
30
20
10
0
-60
-30
0
30
60
90
120
V
CC
= 2V
V
CC
= 4V
V
CC
= 3V
V
CC
= 5V
SWT = V
CC
ALL OUTPUTS
UNLOADED
70
80
PROPAGATION DELAY (µs)
PROPAGATION DELAY (µs)
V
IH
TO V
OL
V
IN
= 20mV
OVERDRIVE = 15mV
60
70
50
60
40
50
V
CC
FALLING
15mV OVERDRIVE
EXTERNAL PROGRAMMING MODE
-60
-30
0
30
60
90
120
150
30
150
-60
-30
0
30
60
90
120
150
TEMPERATURE (°C)
TEMPERATURE (°C)
40
TEMPERATURE (°C)
LOW-LINE COMPARATOR
PROPAGATION DELAY vs. TEMPERATURE
MAX792-3a
POWER-UP RESET DELAY
vs. TEMPERATURE
MAX792-4
NOMINAL WATCHDOG TIMEOUT
PERIOD vs. V
CC
NOMINAL WATCHDOG TIMEOUT PERIOD (s)
MAX792-5
600
500
V
CC
= 5V
300
250
200
3.0
PROPAGATION DELAY (µs)
2.5
400
DELAY (ms)
150
100
50
0
2.0
300
V
CC
= 3V
V
CC
FALLING
15mV OVERDRIVE
EXTERNAL PROGRAMMING MODE
-60
-30
0
30
60
90
120
150
200
100
1.5
1.0
-60
-30
0
30
60
90
120
150
2
3
V
CC
(V)
4
5
TEMPERATURE (°C)
TEMPERATURE (°C)
_________________________________________________________________________________________________
5
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