MAX812LEUS-T ,Microprocessor voltage monitor with manual reset input. Reset threshold voltage 4.63V. Push-pull active-high reset output.General Description ________
MAX812LEUS-T ,Microprocessor voltage monitor with manual reset input. Reset threshold voltage 4.63V. Push-pull active-high reset output.Applicationsto complete the part number.ComputersRESET THRESHOLDControllersSUFFIX VOLTAGE (V)Intell ..
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MAX811LEUS-T-MAX811MEUS-T-MAX811REUS T-MAX811REUS-T-MAX811SEUS/T-MAX811SEUS-T-MAX811TEUS-T-MAX812LEUS-T-MAX812MEUS-T-MAX812REUS-T-MAX812SEUS-T-MAX812TEUS-T
Microprocessor voltage monitor with manual reset input. Reset threshold voltage 4.63V
________________General DescriptionThe MAX811/MAX812 are low-power microprocessor
(µP) supervisory circuits used to monitor power sup-
plies in µP and digital systems. They provide excellent
circuit reliability and low cost by eliminating external
components and adjustments when used with 5V-
powered or 3V-powered circuits. The MAX811/MAX812
also provide a debounced manual reset input.
These devices perform a single function: They assert a
reset signal whenever the VCCsupply voltage falls
below a preset threshold, keeping it asserted for at
least 140ms after VCChas risen above the reset thresh-
old. The only difference between the two devices is that
the MAX811 has an active-low RESEToutput (which is
guaranteed to be in the correct state for VCC down to
1V), while the MAX812 has an active-high RESET out-
put. The reset comparator is designed to ignore fast
transients on VCC. Reset thresholds are available for
operation with a variety of supply voltages.
Low supply current makes the MAX811/MAX812 ideal
for use in portable equipment. The devices come in a
4-pin SOT143package.
________________________ApplicationsComputers
Controllers
Intelligent Instruments
Critical µP and µC Power Monitoring
Portable/Battery-Powered Equipment
____________________________FeaturesPrecision Monitoring of 3V, 3.3V, and 5V
Power-Supply Voltages6µA Supply Current140ms Min Power-On Reset Pulse Width;REESSEETT
Output (MAX811), RESET Output (MAX812)Guaranteed Over TemperatureGuaranteed RREESSEETT
Valid to VCC= 1V (MAX811)Power-Supply Transient ImmunityNo External Components4-Pin SOT143Package
MAX811/MAX812
4-Pin µP Voltage Monitors
with Manual Reset Input
___________________Pin Configuration
___________Typical Operating Circuit19-0411; Rev 3; 3/99
MAX811/MAX812
4-Pin µP Voltage Monitors
with Manual Reset Input
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS(VCC= 5V for L/M versions, VCC= 3.3V for T/S versions, VCC= 3V for R version, TA= -40°C to +85°C, unless otherwise noted.
Typical values are at TA= +25°C.) (Note 1)
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.
Terminal Voltage (with respect to GND)
VCC......................................................................-0.3V to 6.0V
All Other Inputs.......................................-0.3V to (VCC+ 0.3V)
Input Current, VCC,MR.......................................................20mA
Output Current, RESET or RESET.......................................20mA
Continuous Power Dissipation (TA= +70°C)SOT143(derate 4mW/°C above +70°C)320mW
Operating Temperature Range...........................-40°C to +85°C
Storage Temperature Range.............................-65°C to +160°C
Lead Temperature (soldering, 10sec).............................+300°C
MAX811/MAX812
4-Pin µP Voltage Monitors
with Manual Reset Input
ELECTRICAL CHARACTERISTICS (continued)(VCC= 5V for L/M versions, VCC= 3.3V for T/S versions, VCC= 3V for R version, TA= -40°C to +85°C, unless otherwise noted.
Typical values are at TA= +25°C.) (Note 1)
Note 1:Production testing done at TA= +25°C, over temperature limits guaranteed by design using six sigma design limits.
Note 2:RESEToutput for MAX811, RESET output for MAX812.
Note 3:“Glitches” of 100ns or less typically will not generate a reset pulse.
MAX811/MAX812
4-Pin µP Voltage Monitors
with Manual Reset InputPOWER-UP RESET TIMEOUT
vs. TEMPERATURE
MAX811/12-TOC5
TEMPERATURE (°C)
POWER-UP RESET TIMEOUT (ms)
RESET THRESHOLD DEVIATION
vs. TEMPERATURE
MAX811/12-TOC6
TEMPERATURE (°C)
NORMALIZED THRESHOLD (V)0.9985
POWER-DOWN RESET DELAY vs. TEMPERATURE
(MAX81_L/M)
MAX811/12-TOC4
TEMPERATURE (°C)
POWER-DOWN RESET DELAY (
__________________________________________Typical Operating Characteristics
(TA = +25°C, unless otherwise noted.)
MAX811/MAX812
4-Pin µP Voltage Monitors
with Manual Reset Input
______________________________________________________________Pin Description
_______________Detailed Description
Reset OutputA microprocessor’s (µP’s) reset input starts the µP in a
known state. These µP supervisory circuits assert reset
to prevent code execution errors during power-up,
power-down, or brownout conditions.
RESETis guaranteed to be a logic low for VCC> 1V.
Once VCCexceeds the reset threshold, an internal
timer keeps RESETlow for the reset timeout period;
after this interval, RESETgoes high.
If a brownout condition occurs (VCCdips below the
reset threshold), RESETgoes low. Any time VCCgoes
below the reset threshold, the internal timer resets to
zero, and RESETgoes low. The internal timer starts
after VCCreturns above the reset threshold, and RESET
remains low for the reset timeout period.
The manual reset input (MR) can also initiate a reset.
See the Manual Reset Inputsection.
The MAX812 has an active-high RESET output that is
the inverse of the MAX811’s RESEToutput.
Manual Reset InputMany µP-based products require manual reset capabil-
ity, allowing the operator, a test technician, or external
logic circuitry to initiate a reset. A logic low on MR
asserts reset. Reset remains asserted while MRis low,
and for the Reset Active Timeout Period (tRP) after MR
returns high. This input has an internal 20kΩpull-up
resistor, so it can be left open if it is not used. MRcan
be driven with TTL or CMOS-logic levels, or with open-
drain/collector outputs. Connect a normally open
momentary switch from MRto GND to create a manual-
reset function; external debounce circuitry is not
required. If MRis driven from long cables or if the
device is used in a noisy environment, connecting a
0.1µF capacitor from MRto ground provides additional
noise immunity.
Reset Threshold AccuracyThe MAX811/MAX812 are ideal for systems using a 5V
±5% or 3V ±5% power supply with ICs specified for 5V
±10% or 3V ±10%, respectively. They are designed to
meet worst-case specifications over temperature. The
reset is guaranteed to assert after the power supply
falls out of regulation, but before power drops below
the minimum specified operating voltage range for the
system ICs. The thresholds are pre-trimmed and exhibit
tight distribution, reducing the range over which an
undesirable reset may occur.
MAX811/MAX812
__________Applications Information
Negative-Going VCCTransientsIn addition to issuing a reset to the µP during power-up,
power-down, and brownout conditions, the MAX811/
MAX812 are relatively immune to short duration nega-
tive-going VCCtransients (glitches).
Figure 1 shows typical transient durations vs. reset
comparator overdrive, for which the MAX811/MAX812
do not generate a reset pulse. This graph was generat-
ed using a negative-going pulse applied to VCC, start-
ing above the actual reset threshold and ending below
it by the magnitude indicated (reset comparator over-
drive). The graph indicates the typical maximum pulse
width a negative-going VCCtransient may have without
causing a reset pulse to be issued. As the magnitude
of the transient increases (goes farther below the reset
threshold), the maximum allowable pulse width
decreases. Typically, a VCCtransient that goes 125mV
below the reset threshold and lasts 40µs or less
(MAX81_L/M) or 20µs or less (MAX81_T/S/R) will not
cause a reset pulse to be issued. A 0.1µF capacitor
mounted as close as possible to VCCprovides addi-
tional transient immunity.
Ensuring a Valid RESETOutput
Down to VCC= 0VWhen VCCfalls below 1V, the MAX811 RESEToutput
no longer sinks current—it becomes an open circuit.
Therefore, high-impedance CMOS-logic inputs con-
nected to the RESEToutput can drift to undetermined
voltages. This presents no problem in most applica-
tions, since most µP and other circuitry is inoperative
with VCCbelow 1V. However, in applications where theRESEToutput must be valid down to 0V, adding a pull-
down resistor to the RESETpin will cause any stray
leakage currents to flow to ground, holding RESETlow
(Figure 2). R1’s value is not critical; 100kΩis large
enough not to load RESETand small enough to pull
RESETto ground.
A 100kΩpull-up resistor to VCCis also recommended
for the MAX812 if RESET is required to remain valid for
VCC< 1V.
4-Pin µP Voltage Monitors
with Manual Reset Input
