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MAX811
4-Pin µP Voltage Monitors with Manual RESET Input
MAX811/MAX8124-Pin µP Voltage Monitors
with Manual Reset Input
General Description
The 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.
Applications
Computers
Controllers
Intelligent Instruments
Critical µP and µC Power Monitoring
Portable/Battery-Powered Equipment
Benefits and FeaturesIntegrated Voltage Monitor Increases System
Robustness with Added Manual ResetPrecision Monitoring of 3V, 3.3V, and 5V
Power-Supply Voltages140ms Min Power-On-Reset Pulse Width
- RESETOutput (MAX811), RESET Output (MAX812)Guaranteed Over TemperatureGuaranteed RESETValid to VCC= 1V (MAX811)Power-Supply Transient ImmunitySaves Board SpaceNo External Components4-Pin SOT143 PackageLow Power Consumption Simplifies Power-Supply
Requirements6µA Supply Current
VCC(RESET) RESET
GND
MAX811
MAX812
SOT143
TOP VIEW
( ) ARE FOR MAX812
NOTE: SEE PACKAGE INFORMATION FOR MARKING INFORMATION.
Pin Configuration
MAX811
MAX812
VCC
VCC
RESET
(RESET)
RESET
INPUT
GND
VCC
GND
( ) ARE FOR MAX812PUSHBUTTON
SWITCH
Typical Operating Circuit
PART*
MAX811_EUS-T
MAX812_EUS-T-40°C to +85°C
-40°C to +85°C
TEMP RANGEPIN-PACKAGE
4 SOT143
4 SOT143
Ordering Information
*This part offers 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 are available in both leaded and lead(Pb)-free packaging.
Specify lead-free by replacing “-T” with “+T” when ordering.
RESET THRESHOLD
SUFFIXVOLTAGE (V)4.634.383.082.932.63
MAX811/MAX8124-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
ISOURCE= 150µA, 1.8V < VCC< VTH(MIN)
MAX81_R/S/T, VCC= 3.6V, IOUT= 0
MAX81_L/M, VCC= 5.5V, IOUT= 0= -40°C to +85°C
VOD= 125mV, MAX81_R/S/T
VOD= 125mV, MAX81_L/M
MAX81_S
MAX81_L
MAX81_M
VCC= VTH(MAX)
CONDITIONS
0.8 x VCC
2.3VIH0.5tMDMRto Reset Propagation Delay
(Note 2)100MRGlitch Immunity (Note 3)10tMRMRMinimum Pulse Width140560tRPReset Active Timeout Period2.710ICCSupply Current6151.2VCCOperating Voltage Range20VCCto Reset Delay (Note 2)40
3.033.083.14Reset Threshold
UNITSMINTYPMAXSYMBOLPARAMETER
MAX812L/M only, ISINK= 3.2mA,
MAX812R/S/T only, ISINK= 1.2mA,
VCC= VTH(MAX)V
VOL
RESET Output Voltage
(MAX812)
VOH
VCC> VTH(MAX), MAX81_L/M0.8VIL
VCC> VTH(MAX), MAX81_R/S/T
0.25 x VCCVILInput Threshold0.7 x VCCVIH102030MRPull-Up Resistance= 0°C to +70°C1.05.5
ppm/°C30Reset Threshold Tempco
MAX81_R2.582.632.68
TA = +25°C
TA = -40°C to +85°C
TA = +25°C
TA = -40°C to +85°C
MAX81_TTA = +25°C
TA = -40°C to +85°C
TA = +25°C
TA = -40°C to +85°C
TA = +25°C
TA = -40°C to +85°C
VTHV
MAX811/MAX8124-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.
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.
MAX811R/S/T only, ISINK= 1.2mA,
VCC= VTH(MIN)
MAX811L/M only, ISOURCE= 800µA,
VCC> VTH(MAX)
MAX811L/M only, ISINK= 3.2mA,
VCC= VTH(MIN)
ISINK= 50µA, VCC> 1.0V
MAX811R/S/T only, ISOURCE= 500µA,
VCC> VTH(MAX)
CONDITIONS
VCC- 1.5
VOH
RESETOutput Voltage
(MAX811)
VOL
0.8 x VCC
UNITSMINTYPMAXSYMBOLPARAMETER
MAX811/MAX8124-Pin μP Voltage Monitors
with Manual Reset Input
POWER-UP RESET TIMEOUT
vs. TEMPERATURE
MAX811/12-TOC5
TEMPERATURE (°C)
POWER-UP RESET TIMEOUT (ms)
MAX81_R/S/T
MAX81_L/M
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 (
VOD = VTH - VCC
VOD = 125mV
VOD = 200mV
VOD = 20mV
Typical Operating Characteristics
(TA = +25°C, unless otherwise noted.)
SUPPLY CURRENT vs. TEMPERATURE
(MAX81_R/S/T)
MAX811/12-TOC1
TEMPERATURE (°C)
SUPPLY CURRENT (
VCC = 3.6V
VCC = 3.3V
VCC = 1V
SUPPLY CURRENT vs. TEMPERATURE
(MAX81_L/M)
MAX811/12-TOC2
TEMPERATURE (°C)
SUPPLY CURRENT (
VCC = 5.5V
VCC = 3V
VCC = 1V
POWER-DOWN RESET DELAY vs. TEMPERATURE
(MAX81_R/S/T)
MAX811/12-TOC3
TEMPERATURE (°C)
POWER-DOWN RESET DELAY (
VOD = VTH - VCC
VOD = 20mV
VOD = 200mV
VOD = 125mV
MAX811/MAX8124-Pin μP Voltage Monitors
with Manual Reset Input
Pin Description
Detailed Description
Reset Output
A 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 Input
Many 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 Accuracy
The 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.
Manual Reset Input. A logic low on MRasserts reset. Reset remains asserted as long as MRis
low and for 180ms after MRreturns high. This active-low input has an internal 20kΩpull-up
resistor. It can be driven from a TTL or CMOS-logic line, or shorted to ground with a switch.
Leave open if unused.3
+5V, +3.3V, or +3V Supply Voltage44
Active-High Reset Output. RESET remains high while VCCis below the reset threshold or whileis held low. RESET remains high for Reset Active Timeout Period (tRP) after the reset condi-
tions are terminated.—
Active-Low Reset Output. RESETremains low while VCCis below the reset threshold or whileis held low. RESETremains low for the Reset Active Timeout Period (tRP) after the reset
conditions are terminated.2
Ground11
FUNCTION
PIN
VCC
RESET
RESET
GND
NAME
MAX811MAX812
MAX811/MAX8124-Pin μP Voltage Monitors
with Manual Reset Input
Applications Information
Negative-Going VCCTransients
In 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= 0V
When 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 the
RESEToutput 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.1001000
RESET COMPARATOR OVERDRIVE , VTH - VCC (mV)
MAXIMUM TRANSIENT DURATION (ms)
TA = +25°C
MAX81 _L/M
MAX81 _R/S/T
VCC
GND
MAX811
RESET
Figure 1. Maximum Transient Duration without Causing a
Reset Pulse vs. Comparator Overdrive
Figure 2. RESETValid to VCC= Ground Circuit

Partno	Mfg	Dc	Qty	Available	Descript
MAX811	MAX	N/a	193	avai	4-Pin µP Voltage Monitors with Manual RESET Input