MAX821MUS+T ,4-Pin, µP Voltage Monitors with Pin-Selectable Power-On Reset Timeout DelayApplicationsMAX822LUS-T4.63 BF_ _Bar-Code ScannersMAX822MUS-T 4.38 BG_ _ComputersMAX822TUS-T 3.08 B ..
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MAX821PUS ,4-Pin, µP Voltage Monitors with Pin-Selectable Power-On Reset Timeout DelayFeaturesThe MAX821/MAX822 microprocessor (µP) supervisory♦ Pin-Selectable, Precision Power-On Reset ..
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MAX821PUS-T ,Microprocessor voltage monitor with pin-selectable power-on reset timeout delay (1ms,max, 20ms,min or 100ms,min). Reset threshold(nom) 4.00V. Active-low reset output.ApplicationsMAX822LUS-T 4.63 BF_ _Bar-Code ScannersMAX822MUS-T 4.38 BG_ _ComputersMAX822TUS-T 3.08 ..
MAX821RUS+T ,4-Pin, µP Voltage Monitors with Pin-Selectable Power-On Reset Timeout DelayELECTRICAL CHARACTERISTICS(V = full range, T = -40°C to +125°C, unless otherwise noted. Typical val ..
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MAX821LUS+T-MAX821MUS+T-MAX821PUS-MAX821PUS+T-MAX821RUS+T-MAX821S-MAX821SUS-MAX821SUS+T-MAX821TUS+T-MAX822RUS+T-MAX822TUS+T
4-Pin, µP Voltage Monitors with Pin-Selectable Power-On Reset Timeout Delay
General DescriptionThe MAX821/MAX822 microprocessor (µP) supervisory
circuits monitor power supplies in µP and digital sys-
tems. They provide excellent circuit reliability and low
cost by eliminating external components and adjust-
ments when used with 5V-powered or 3V-powered cir-
cuits. The MAX821/MAX822 also provide a power-on
reset timeout delay that is pin selectable to 1ms (max),
20ms (min), or 100ms (min).
These devices perform a single function: they assert a
reset signal whenever the VCCsupply voltage falls
below a preset threshold, and they keep reset asserted
for the pin-selected reset timeout delay after VCChas
risen above the reset threshold. The only difference
between the two devices is that the MAX821 has an
active-low RESEToutput (which is guaranteed to be in
the correct state for VCCdown to 1V), while the
MAX822 has an active-high RESET output. The reset
comparator is designed to ignore fast transients on
VCC. Reset thresholds suitable for operation with a vari-
ety of supply voltages are available.
Low supply current makes the MAX821/MAX822 ideal
for use in portable equipment. These devices come in a
4-pin SOT143 package.
________________________ApplicationsBar-Code Scanners
Computers
Controllers
Intelligent Instruments
Critical µP and µC Power Monitoring
Portable/Battery-Powered Equipment
FeaturesPin-Selectable, Precision Power-On Reset Delay:
1ms (max), 20ms (min), or 100ms (min)Precision Monitoring of +3V to +5V Power-Supply
Voltages2.5µA Supply CurrentGuaranteed Over Temperature (-40°C to +125°C)Guaranteed RESETValid to VCC= 1V (MAX821)Power-Supply Transient ImmunityNo External ComponentsSOT143 Package
MAX821/MAX822
4-Pin µP Voltage Monitors with Pin-Selectable
Power-On Reset Timeout DelayVCC
SRT(RESET) RESET
GND
MAX821
MAX822
SOT143TOP VIEW
( ) ARE FOR MAX822
Pin ConfigurationMAX821
MAX822
VCC
RESET
(RESET)
RESET
INPUT
GND
VCC
GND
( ) ARE FOR MAX822
SRT
20ms
100ms
1ms
__________Typical Operating Circuit19-1122; Rev 3; 12/05
PART
MAX821LUS-TMAX821MUS-T4.38
NOMINAL VTH(V)TOP MARK*
AZ_ _
BA_ _
Ordering Information* The first two letters in the package top mark identify the part,
while the remaining two letters are the lot-tracking code.
Devices are available in both leaded and lead-free packaging.
Specify lead-free by replacing “-T” with “+T” when ordering.
MAX821PUS-T4.00BM_ _
MAX821TUS-T3.08BB_ _
MAX821SUS-T2.93BC_ _
MAX821UUS-T2.78BL_ _
MAX821RUS-T2.63BD_ _
MAX822LUS-T4.63BF_ _
MAX822MUS-T4.38BG_ _
MAX822TUS-T3.08BH_ _
MAX822SUS-T2.93BJ_ _
MAX822RUS-T2.63BK_ _
MAX821/MAX822
4-Pin µP Voltage Monitors with Pin-Selectable
Power-On Reset Timeout Delay
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS(VCC= full range, TA= -40°C to +125°C, unless otherwise noted. Typical values are at TA= +25°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.
Terminal Voltage (with respect to GND)
VCC......................................................................-0.3V to 6.0V
All Other Inputs.......................................-0.3V to (VCC+ 0.3V)
Input Current, VCC, SRT......................................................20mA
Output Current, RESET or RESET.......................................20mA
Continuous Power Dissipation (TA= +70°C)
SOT143-4 (derate 4mW/°C above +70°C)...................320mW
Operating Temperature Range.........................-40°C to +125°C
Storage Temperature Range.............................-65°C to +160°C
Lead Temperature (soldering, 10sec).............................+300°C
SRT = unconnected
0.5VCCVOPEN
SRT Input Threshold0.9VCCVIH
0.07VCCVIL
tRPReset Active Timeout Period203240
1.05.5VCCRange
0.50.8150VCCto Reset Delay (Note 1)
ppm/°C30Reset Threshold Tempco
VTHReset Threshold (Note 1)
1.85.5µA
ICCSupply Current
UNITSMINTYPMAXSYMBOLPARAMETER= -40°C to +85°C= 0°C to +70°C
VCCfalling at 1mV/µs
RESET= low for MAX821,
RESET = high for MAX822
MAX82_R
MAX82_L/M/P,
VCC= 5.5V, IOUT= 0
MAX82_R/S/T/U,
VCC= 5.5V, IOUT= 0
CONDITIONSMAX82_L
MAX82_M
MAX82_P
MAX82_S
MAX82_U1
SRT Input Current (Note 2)100
-100RESET= low for MAX821,
RESET = high for MAX822
SRT = GND
SRT = VCC= +25°C= +25°C= +25°C= +25°C= +25°C
MAX82_TTA= +25°C= +25°C= +25°C= +25°C
SRT = GND
SRT = unconnected
SRT = VCC= -40°C to +125°C= -40°C to +125°C= -40°C to +125°C= -40°C to +125°C= -40°C to +125°C= -40°C to +125°C= -40°C to +125°C= TMINto TMAX= TMINto TMAX
MAX821/MAX822
4-Pin µP Voltage Monitors with Pin-Selectable
Power-On Reset Timeout Delay
Note 1:RESEToutput for MAX821; RESET output for MAX822.
Note 2:During reset active timeout period only.
Note 3:Guaranteed by design.
ELECTRICAL CHARACTERISTICS (continued)(VCC= full range, TA= -40°C to +125°C, unless otherwise noted. Typical values are at TA= +25°C.)
SRT Input Capacitance
(Note 3) (see Setting
the Reset Timeout Delay
section)
UNITSMINTYPMAXSYMBOLPARAMETERMAX821R/S/T/U only, ISINK= 1.2mA,
VCC= VTH(MIN)
MAX821L/M/P only, ISINK= 3.2mA,
VCC= VTH(MIN)
Internal
CONDITIONSVOL
ISINK= 50µA
MAX822R/S/T only, ISINK= 1.2mA,
VCC= VTH(MAX)
MAX822L/M only, ISINK= 3.2mA,
VCC= VTH(MAX)
0.8VCC
VOH
RESETOutput Voltage
(MAX821)
VCC-1.5
MAX821R/S/T/U only, ISOURCE= 500µA,
VCC≥VTH(MAX)
MAX821L/M/P only, ISOURCE= 800µA,
VCC≥VTH(MAX)
RESET TIMEOUT PERIOD
vs. TEMPERATURE
MAX 821/822 TOC-04
TEMPERATURE (°C)
RESET TIMEOUT PERIOD (ms)6080
SRT = GND
RESET TIMEOUT PERIOD
vs. TEMPERATURE
MAX 821/822 TOC-05
TEMPERATURE (°C)
RESET TIMEOUT PERIOD (ms)6080
SRT = VCC
RESET TIMEOUT PERIOD
vs. TEMPERATURE
MAX 821/822 TOC-06
TEMPERATURE (°C)
RESET TIMEOUT PERIOD (ms)6080
SRT = UNCONNECTED
VOLV
VOH
RESET Output Voltage
(MAX822)
0.8VCCISOURCE= 150µA, 1.4V ≤VCC≤VTH(MIN)
__________________________________________Typical Operating Characteristics(TA = +25°C, unless otherwise noted.)= 0°C to +70°C,
VCC≥1V
TA = -40°C to +85°C,
VCC≥1.2V
MAX821/MAX822
4-Pin µP Voltage Monitors with Pin-Selectable
Power-On Reset Timeout Delay
____________________________Typical Operating Characteristics (continued)(TA = +25°C, unless otherwise noted.)
NORMALIZED RESET THRESHOLD
vs. TEMPERATURE
MAX 821/822 TOC-07
TEMPERATURE (°C)
NORMALIZED RESET THRESHOLD (V)6080
______________________________________________________________Pin DescriptionGNDGroundRESET
Active-Low Reset Output. RESETis low while VCCis below the reset threshold. It remains
low for the reset timeout period after the reset condition is terminated. The reset timeout
period is determined by the SRT input.RESET
Active-High Reset Output. RESET is high while VCCis below the reset threshold. It remains
high for the reset timeout period after the reset condition is terminated. The reset timeout
period is determined by the SRT input.SRTSet Reset Timeout Input. Connect to GND for 1ms (max) delay; connect to VCCfor 20ms
(min) delay; leave unconnected for 100ms (min) delay.VCCSupply Voltage
PIN
NAMEFUNCTIONMAX821MAX822MAX82_R/S/T POWER-DOWN RESET DELAY
vs. TEMPERATURE
MAX 821/822 TOC-02
TEMPERATURE (°C)
POWER-DOWN RESET DELAY (6080
VCC FALLING AT 1mV/μs
VCC FALLING AT 10mV/μs
MAX82_L/M POWER-DOWN RESET DELAY
vs. TEMPERATURE
MAX 821/822 TOC-03
TEMPERATURE (°C)
POWER-DOWN RESET DELAY (6080
VCC FALLING AT 1mV/μs
VCC FALLING AT 10mV/μs
NORMALIZED SUPPLY
CURRENT vs. TEMPERATURE
MAX 821/822 TOC-01
TEMPERATURE (°C)
NORMALIZED SUPPLY CURRENT (6080
1.10
_______________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. They also provide
a reset timeout delay that is pin programmable to 1ms
(max), 20ms (min), or 100ms (min). This feature allows
flexibility in designing bar-code scanners, hand-held
devices, and other applications that require quick or
nonstandard power-up times.
The MAX821’s RESEToutput is guaranteed to be a
logic low for VCC> 1V. Once VCCexceeds the reset
threshold, an internal timer keeps RESETlow for the
reset timeout period, as determined by the Set Reset
Timeout (SRT) input. See the Setting the Reset Timeout
Delaysection.
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 begins
counting after VCCreturns above the reset threshold,
and RESETremains low for the reset timeout period.
The MAX822 has an active-high RESET output that is
the inverse of the MAX821’s RESEToutput.
Setting the Reset Timeout DelayUse the three-level Set Reset Timeout (SRT) input to set
the reset timeout delay. Connect SRT to GND for a 1ms
(max) delay; connect it to VCCfor a 20ms (min) delay;
or leave it unconnected for a 100ms (min) delay.
If you choose to drive the SRT pin with an external sig-
nal, make sure the signal source can charge/discharge
the capacitance on SRT quickly enough (<500µs) to
avert an unintended reset timeout delay.
To ensure proper operation when selecting the 100ms
timeout (SRT = unconnected), minimize capacitive
loading on the SRT pin (< 200pF). Excessive capacitive
loading can select an unintended faster timeout mode.
Reset Threshold AccuracyThe MAX821/MAX822 are designed to meet their worst-
case specifications over their entire operating tempera-
ture range. Choose a reset threshold guaranteed to
assert at a voltage below the power supply’s regulation
range and above the minimum specified operating volt-
age range for the system’s ICs.
__________Applications Information
Negative-Going VCCTransientsWhile designed to issue a reset to the microprocessor
(µP) during power-up, power-down, and brownout con-
ditions, the MAX821/MAX822 are relatively immune to
short-duration, negative-going VCCtransients (glitches).
Figure 1 shows the maximum transient duration vs. reset
comparator overdrive for which the MAX821/MAX822
typically do not generate a reset pulse. This graph was
generated using a negative-going pulse applied to VCC,
starting above the actual reset threshold and ending
below it by the magnitude indicated (reset comparator
overdrive). The graph indicates the typical maximum
pulse width a negative-going VCCtransient may have
without causing a reset pulse to be issued. As the mag-
nitude of the transient increases (goes farther below the
reset threshold), the maximum allowable pulse width
decreases. Typically, for the MAX821/MAX822, a VCC
transient that goes 100mV below the reset threshold and
lasts 12µs or less will not cause a reset pulse to be
issued. A 0.1µF capacitor mounted as close as possible
to VCCcan provide additional transient immunity, if
desired.
MAX821/MAX822
4-Pin µP Voltage Monitors with Pin-Selectable
Power-On Reset Timeout DelayMAX821/822 FIG-01
RESET COMPARATOR OVERDRIVE, VTH-VCC (mV)
MAXIMUM TRANSIENT DURATION (
TA = +25°C
Figure 1. Maximum Transient Duration Without Causing a
Reset Pulse vs. Comparator Overdrive
MAX821/MAX822
Ensuring a Valid RESETOutput
Down to VCC= 0VWhen VCCfalls below 1V, the MAX821 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 2a). R1’s value is not critical; 100kΩis large
enough not to load RESET, and small enough to pull
RESETto ground.
A 100kΩpull-up resistor to VCCis also recommended
for the MAX822 if RESET is required to remain valid for
VCC< 1V (Figure 2b).
Interfacing to µPs with
Bidirectional Reset PinsµPs with bidirectional reset pins (such as the Motorola
68HC11 series) can contend with the MAX821 reset
output. For example, if the MAX821 RESEToutput is
asserted high and the µP wants to pull it low, indetermi-
nate logic levels may result. To correct such cases,
connect a 4.7kΩresistor between the MAX821 RESET
output and the µP reset I/O (Figure 3). Buffer the reset
output to other system components.
___________________Chip InformationTRANSISTOR COUNT: 492
4-Pin µP Voltage Monitors with Pin-Selectable
Power-On Reset Timeout Delay4.7k
VCC
GND
RESET
MAX821
RESET
VCC
GND
BUFFER
BUFFERED RESET
TO OTHER SYSTEM
COMPONENTS
Figure 3. Interfacing to µPs with Bidirectional Reset I/O
VCC
VCC
GND
MAX821
RESET
VCC
VCC
GND
MAX822
RESET
b)Figure 2. RESET/RESET Valid to VCC= Ground Circuit
