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PDF MAX8211EPA Data sheet ( Hoja de datos )
| Número de pieza | MAX8211EPA | |
| Descripción | Microprocessor Voltage Monitors with Programmable Voltage Detection | |
| Fabricantes | Maxim Integrated | |
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19-0147; Rev. 2; 6/98
Microprocessor and Non-Volatile
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:
1) µP reset: Assertion of RESET and RESET outputs dur-
ing power-up, power-down, and brownout condi-
tions. RESET is guaranteed valid for VCC down to 1V.
2) Manual-reset input.
3) 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.
4) Watchdog fault output: Assertion of WDO if the watch-
dog input is not toggled within a preset timeout
period.
5) Pulsed watchdog output: Advance warning of
impending WDO assertion from watchdog timeout
that causes hardware shutdown.
6) 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%).
Applications
Computers
Controllers
Intelligent Instruments
Critical µP Power Monitoring
Features
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)
Ordering Information
PART**
TEMP. RANGE
PIN-PACKAGE
MAX792_CPE
0°C to +70°C
16 Plastic DIP
MAX792_CSE
0°C to +70°C
16 Narrow SO
MAX792_C/D
0°C to +70°C
Dice*
Ordering Information continued at end of data sheet.
* Dice are tested at TA = +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
RESET THRESHOLD (V)
L 4.62
M 4.37
T 3.06
S 2.91
R 2.61
Typical Operating Circuit
VCC
3 0.1µF
VCC
4
CE OUT
RESET IN/INT
13
VCC
MAX792
5 LLIN/
14
CE IN
REFOUT
OVO 6
ADDRESS
DECODER
µP
RAM
A0-A15
7 OVI
LOW LINE 10
RESET 1
NMI
RESET
8 SWT
MR 9
GND
12
GND
________________________________________________________________ Maxim Integrated Products 1
For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800.
For small orders, phone 1-800-835-8769.
1 page  
Microprocessor and Non-Volatile
Memory Supervisory Circuits
__________________________________________Typical Operating Characteristics
(TA = +25°C, unless otherwise noted.)
SUPPLY CURRENT vs. TEMPERATURE
100
90 VCC = 5V
80
SWT = VCC
ALL OUTPUTS
UNLOADED
70
VCC = 4V
60
50 VCC = 3V
40
30
20
10 VCC = 2V
0
-60 -30
0 30 60 90 120 150
TEMPERATURE (°C)
OVERVOLTAGE COMPARATOR
PROPAGATION DELAY vs. TEMPERATURE
70
60
50
40
VIH TO VOL
VIN = 20mV
OVERDRIVE = 15mV
30
-60 -30 0 30 60 90
TEMPERATURE (°C)
120 150
RESET COMPARATOR
PROPAGATION DELAY vs. TEMPERATURE
80
70
60
50
VCC FALLING
15mV OVERDRIVE
EXTERNAL PROGRAMMING MODE
40
-60 -30 0 30 60 90
TEMPERATURE (°C)
120 150
LOW-LINE COMPARATOR
PROPAGATION DELAY vs. TEMPERATURE
600
500
VCC = 5V
400
300 VCC = 3V
200 VCC FALLING
15mV OVERDRIVE
EXTERNAL PROGRAMMING MODE
100
-60 -30 0 30 60 90 120 150
TEMPERATURE (°C)
POWER-UP RESET DELAY
vs. TEMPERATURE
300
250
200
150
100
50
0
-60 -30
0 30 60 90 120 150
TEMPERATURE (°C)
NOMINAL WATCHDOG TIMEOUT
PERIOD vs. VCC
3.0
2.5
2.0
1.5
1.0
2
3
VCC (V)
4
5
_________________________________________________________________________________________________ 5
5 Page 
Microprocessor and Non-Volatile
Memory Supervisory Circuits
REGULATOR
R3 VCC
RESET IN/INT
RESET 2
TO µP
R1
R4
MAX792
MAX820
LLIN/REFOUT
RESET 1
TO µP
R2
( )VLOW LINE = 1.3 R1 + R2
R2
( )VRESET = 1.3 R3 + R4
R4
LOW LINE 10
GND
TO µP NMI
Figure 4c. Alternative Connection for External Programming Mode
Reset Outputs (RESET and RESET)
The RESET output is active low and typically sinks 1.6mA
at 0.1V. When deasserted, RESET sources 1.6mA at typi-
cally VCC - 1.5V. The RESET output is the inverse of
RESET. RESET is guaranteed to be valid down to VCC = 1V,
and an external 10kΩ pull-down resistor on RESET
ensures that it will be valid with VCC down to GND
(Figure 5). As VCC goes below 1V, the gate drive to the
RESET output switch reduces accordingly, increasing the
rDS(ON) and the saturation voltage. The 10kΩ pull-down
resistor ensures that the parallel combination of switch
plus resistor will be around 10kΩ and the saturation
voltage will be below 0.4V while sinking 40µA. When
using an external pull-down resistor of 10kΩ, the high
state for the RESET output with VCC = 4.75V is typically
4.60V.
Overvoltage Comparator
The overvoltage comparator is an uncommitted com-
parator that has no effect on the operation of other chip
functions. Use this input to provide overvoltage indica-
tion by connecting a voltage divider from the input sup-
ply, as in Figure 6.
Connect OVI to ground if the overvoltage function is not
used. OVO goes low when OVI goes above 1.30V. With
OVI below 1.30V, OVO is actively pulled to VCC and can
source1µA.
1
RESET
MAX792
MAX820
TO µP RESET
10k
Figure 5. Adding an external pull-down resistor ensures RESET
is valid with VCC down to GND.
VOLTAGE REGULATOR
3
VCC
7 OVI
MAX792
MAX820
OVO 6
OVERVOLTAGE
1.30V
GND
12
Figure 6. Detecting an Overvoltage Condition
Watchdog Function
The watchdog monitors µP activity via the watchdog
input (WDI). If the µP becomes inactive, WDO and WDPO
are asserted. To use the watchdog function, connect
WDI to a µP bus line or I/O line. If WDI remains high or
low for longer than the watchdog timeout period
(1.6sec nominal), WDPO and WDO are asserted, indicat-
ing a software fault condition (see Watchdog-Pulse
Output and Watchdog Output sections).
Watchdog Input
If the watchdog function is unused, connect WDI to VCC
or GND. A change of state (high-to-low, low-to-high, or
a minimum 100ns pulse) at WDI during the watchdog
period resets the watchdog timer. The watchdog timer
______________________________________________________________________________________ 11
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