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MAX6822LUK+T-MAX6822RUK+T-MAX6822ZUK+T-MAX6823RUK+T-MAX6823SUK+T-MAX6823VUK+T-MAX6823WUK+T
Low-Voltage SOT23 µP Supervisors with Manual Reset and Watchdog Timer
●Set-Top Boxes●Computers and Con- trollers●Embedded Controllers●Intelligent Instruments●Critical µP Monitoring●Portable/Battery- Powered Equipment
General DescriptionThe MAX6821–MAX6825 are low-voltage microproces-
sor (µP) supervisory circuits that combine voltage mon-
itoring, watchdog timer, and manual reset input func-
tions in a 5-pin SOT23 package. Microprocessor super-
visory circuits significantly improve system reliability and
accuracy compared to separate ICs or discrete compo-
nents. These devices assert a reset signal whenever the
monitored voltage drops below its preset threshold, keep-
ing it asserted for a minimum timeout period after VCC rises
above the threshold. In addition, a watchdog timer monitors
against code execution errors. A debounced manual reset
is also available. The MAX6821–MAX6825 monitor voltag-
es from +1.8V to +5.0V. These outputs are guaranteed to
be in the correct state for VCC down to +1.0V.
Nine preprogrammed reset threshold voltages are
available (see the Threshold Suffix Guide). The
MAX6821, MAX6822, and MAX6823 all have a manual
reset input and a watchdog timer. The MAX6821 has
push-pull RESET, the MAX6822 has open-drain RESET,
and the MAX6823 has push-pull RESET. The MAX6824
has a watchdog timer and both push-pull RESET and
push-pull RESET. The MAX6825 has a manual reset
input and both push-pull RESET and push-pull RESET.
The Selector Guide explains the functions offered in
this series of parts.
Features●Monitors +1.8V, +2.5V, +3.0V, +3.3V, +5.0V Supplies●140ms (min) Reset Timeout Delay●1.6s Watchdog Timeout Period (MAX6821/MAX6822/
MAX6823/MAX6824)●Manual Reset Input (MAX6821/MAX6822/MAX6823/
MAX6825)●Three Reset Output Options
Push-Pull RESET Push-Pull RESET
Open-Drain RESET●Guaranteed Reset Valid to VCC = +1.0V●Immune to Short Negative VCC Transients●No External Components●Small 5-Pin SOT23 Packages
Applications
Note: Bold indicates standard versions. Samples are typically available for standard versions only. All parts require a 2.5k
minimum order increment. Contact factory for availability.
*Insert the desired suffix letter (from the table below) into the
blank to complete the part number
Devices are available in both leaded and lead(Pb)-free packag-
ing.Specify lead-free by replacing “-T” with “+T” when ordering.
SUFFIXRESET
THRESHOLD (V)4.634.383.08
2.93
2.63
2.322.191.67
1.58
PART*TEMP RANGEPIN-PACKAGE
MAX6821_UK-T-40°C to +125°C5 SOT23-5
MAX6822_UK-T-40°C to +125°C5 SOT23-5
MAX6823_UK-T-40°C to +125°C5 SOT23-5
MAX6824_UK-T -40°C to +125°C5 SOT23-5
MAX6825_UK-T-40°C to +125°C5 SOT23-5
GND
WDIMR5VCCRESET(RESET)
(RESET) MAX6821 ONLY
MAX6821
MAX6822
MAX6823
SOT23-5TOP VIEW4
MAX6821/MAX6825Low-Voltage SOT23 µP Supervisors
with Manual Reset and Watchdog TimerSelector Guide appears at end of data sheet.
Threshold Sufix Guide
Ordering InformationTypical Operating Circuit appears at end of data sheet.
Pin Configurations continued at end of data sheet.
Pin Conigurations
VCC to GND .........................................................-0.3V to +6.0V
Open-Drain RESET ..............................................-0.3V to +6.0V
Push-Pull RESET, RESET, MR, WDI .......-0.3V to (VCC + 0.3V)
Input Current (VCC) ............................................................20mA
Output Current (RESET, RESET) ......................................20mA
Continuous Power Dissipation (TA = +70°C)5-Pin SOT23 (derate 7.1mW/°C above +70°C) ..........571mW
Operating Temperature Range .........................-40°C to +125°C
Junction Temperature ......................................................+150°C
Storage Temperature Range ............................-65°C to +150°C
Lead Temperature (soldering, 10s) .................................+300°C
(VCC = +4.5V to +5.5V for MAX682_L/M, VCC = +2.7V to +3.6V for MAX682_T/S/R, VCC = +2.1V to +2.75V for MAX682_Z/Y, VCC =
+1.53V to +2.0V for MAX682_W/V, TA = -40°C to +125°C, unless otherwise specified. Typical values are at TA = +25°C.) (Note 1)
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITSOperating Voltage RangeVCCTA = 0°C to +85°C1.05.5VTA = -40°C to +125°C1.25.5
VCC Supply Current
(MR and WDI Unconnected)ICC
VCC = +5.5V, no loadTA = -40°C to +85°C1020
TA = -40°C to +125°C30
VCC = +3.6V, no loadTA = -40°C to +85°C716
TA = -40°C to +125°C25
VCC = +3.6V, no load
(MAX6825 only)
TA = -40°C to +85°C512
TA = -40°C to +125°C20
VCC Reset Threshold
(VCC Falling)VTH
MAX682_L TA = -40°C to +85°C4.504.634.75
TA = -40°C to +125°C4.474.634.78
MAX682_M TA = -40°C to +85°C4.254.384.50
TA = -40°C to +125°C4.224.384.53
MAX682_T TA = -40°C to +85°C3.003.083.15
TA = -40°C to +125°C2.973.083.17
MAX682_STA = -40°C to +85°C2.852.933.00
TA = -40°C to +125°C2.832.933.02
MAX682_R
TA = -40°C to +85°C2.552.632.70
TA = -40°C to +125°C2.532.632.72
MAX682_Z TA = -40°C to +85°C2.252.322.38
TA = -40°C to +125°C2.242.322.40
MAX682_Y TA = -40°C to +85°C2.122.192.25
TA = -40°C to +125°C2.112.192.27
MAX682_W TA = -40°C to +85°C1.621.671.71
TA = -40°C to +125°C1.611.671.72
MAX682_V TA = -40°C to +85°C1.521.581.62
Reset Threshold Temperature
Coefficient60ppm/°C
Reset Threshold Hysteresis2 × VTHmV
MAX6821/MAX6825Low-Voltage SOT23 µP Supervisors
with Manual Reset and Watchdog Timer
Electrical CharacteristicsStresses 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.
Absolute Maximum Ratings
Note 1: Over-temperature limits are guaranteed by design and not production tested. Devices tested at TA = +25°C.
Note 2: Guaranteed by design and not production tested.
(VCC = +4.5V to +5.5V for MAX682_L/M, VCC = +2.7V to +3.6V for MAX682_T/S/R, VCC = +2.1V to +2.75V for MAX682_Z/Y, VCC =
+1.53V to +2.0V for MAX682_W/V, TA = -40°C to +125°C, unless otherwise specified. Typical values are at TA = +25°C.) (Note 1)
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITSReset Timeout PeriodtRPTA = -40°C to +85°C140200280msTA = -40°C to +125°C100320
RESET Output LOW
(Push-Pull or Open-Drain)VOL
VCC ≥ 1.0V, ISINK = 50µA, reset asserted,
TA = 0°C to +85°C0.3VCC ≥ 1.2V, ISINK = 100µA, reset asserted0.3
VCC ≥ 2.55V, ISINK = 1.2mA, reset asserted0.3
VCC ≥ 4.25V, ISINK = 3.2mA, reset asserted0.4
RESET Output HIGH
(Push-Pull Only)VOH
VCC ≥ 1.8V, ISOURCE = 200µA, reset not
asserted0.8 × VCCVCC ≥ 3.15V, ISOURCE = 500µA, reset not
asserted0.8 × VCC
VCC ≥ 4.75V, ISOURCE = 800µA, reset not
asserted0.8 × VCC
Open-Drain RESET Output
Leakage Current (Note 1)ILKGVCC > VTH, RESET not asserted1.0µA
RESET Output HIGH
(Push-Pull Only)VOH
VCC ≥ 1.0V, ISOURCE = 1µA, reset asserted,
TA = 0°C to +85°C0.8 × VCCVCC ≥ 1.50V, ISOURCE = 100µA, reset asserted0.8 × VCC
VCC ≥ 2.55V, ISOURCE = 500µA, reset asserted0.8 × VCC
VCC ≥ 4.25V, ISOURCE = 800µA, reset asserted0.8 × VCC
RESET Output LOW
(Push-Pull Only)VOL
VCC ≥ 1.8V, ISINK = 500µA, reset not asserted0.3VCC ≥ 3.15V, ISINK = 1.2mA, reset not asserted0.3
VCC ≥ 4.75V, ISINK = 3.2mA, reset not asserted0.4
MANUAL RESET INPUT (MAX6821/MAX6822/MAX6823/MAX6825)MR Input VoltageVIL0.3 × VCCVVIH0.7 × VCC
MR Minimum Input Pulse1µs
MR Glitch Rejection100ns
MR to Reset Delay200ns
MR Pullup Resistance255075kΩ
WATCHDOG INPUT (MAX6821/MAX6822/MAX6823/MAX6824)Watchdog Timeout PeriodtWDTA = -40°C to +85°C1.121.602.40sTA = -40°C to +125°C0.802.60
WDI Pulse Width (Note 2)tWDI50ns
WDI Input VoltageVIL0.3 × VCCVVIH0.7 × VCC
WDI Input CurrentIWDIWDI = VCC, time average120160µAWDI = 0, time average-20-15
MAX6821/MAX6825Low-Voltage SOT23 µP Supervisors
with Manual Reset and Watchdog Timer
Electrical Characteristics (continued)
(TA = +25°C, unless otherwise noted.)
VOLTAGE OUTPUT HIGH
vs. SOURCE CURRENT
MAX6821 toc08
OUT
(V)
VCC = +2.9V
VOLTAGE OUTPUT LOW
vs. SINK CURRENT
MAX6821 toc07
OUT
(V)
VCC = +2.9V
MAXIMUM VCC TRANSIENT DURATION
vs. RESET THRESHOLD OVERDRIVE
MAX6821 toc06
RESET THRESHOLD OVERDRIVE (mV), VTH - VCC
TRANSIENT DURATION (
RESET OCCURS
ABOVE CURVE
NORMALIZED RESET THRESHOLD
DELAY vs. TEMPERATURE
MAX6821 toc05
TEMPERATURE (°C)
RESET THRESHOLD (V)
WATCHDOG TIMEOUT PERIOD
vs. TEMPERATURE
MAX6821 toc04
TEMPERATURE (°C)
WATCHDOG TIMEOUT PERIOD (s)
VCC TO RESET OUTPUT DELAY
vs. TEMPERATURE
MAX6821 toc03
TEMPERATURE (°C)
PROPAGATION DELAY (
VCC FALLING, VCC = VTH - 100mV
TEMPERATURE (°C)
RESET TIMEOUT PERIOD
vs. TEMPERATURE
MAX6821 toc02
RESET TIMEOUT PERIOD (ms)
SUPPLY CURRENT
vs. TEMPERATURE
MAX6821 toc01
TEMPERATURE (°C)
SUPPLY CURRENT (
VCC = +5V, L VERSION
VCC = +3.3V, S VERSION
VCC = +1.8V, V VERSION
MAX6821/MAX6825Low-Voltage SOT23 µP Supervisors
with Manual Reset and Watchdog Timer
Typical Operating Characteristics
Detailed Description
RESET/RESET OutputA µP’s reset input starts the µP in a known state. The
MAX6821–MAX6825 µP supervisory circuits assert a
reset to prevent code-execution errors during power-up,
power-down, and brownout conditions. Whenever VCC
falls below the reset threshold, the reset output asserts
low for RESET and high for RESET. Once VCC exceeds
the reset threshold, an internal timer keeps the reset out-
put asserted for the specified reset timeout period (tRP);
after this interval, reset output returns to its original state
(see Figure 2).
Manual Reset InputMany µP-based products require manual reset capabili-
ty, allowing the operator, a test technician, or external
logic circuitry to initiate a reset. On the MAX6821/
MAX6822/MAX6823/MAX6825, a logic low on MR
asserts a reset. Reset remains asserted while MR is
low, and for the timeout period (140ms min) after it
returns high. MR has an internal 50kΩ pullup resistor,
so it can be left open if not used. This input can be dri-
ven with CMOS logic levels or with open-drain/collector
outputs. Connect a normally open momentary switch
from MR to GND to create a manual reset function;
external debounce circuitry is not required. If MR is dri-
ven from long cables or the device is used in a noisy
environment, connect a 0.1µF capacitor from MR to
GND to provide additional noise immunity.
Watchdog InputIn the MAX6821–MAX6824, the watchdog circuit moni-
tors the µP’s activity. If the µP does not toggle (low to
high or high to low) the watchdog input (WDI) within the
watchdog timeout period (1.6s nominal), reset asserts
for the reset timoeout period. The internal 1.6s timer
can be cleared by either a reset pulse or by toggling
WDI. The WDI can detect pulses as short as 50ns.
While reset is asserted, the timer remains cleared and
does not count. As soon as reset is released, the timer
starts counting (see Figure 3).
PIN NUMBERSPIN
NAMEFUNCTION
MAX6821MAX6822MAX6823MAX6824MAX6825111RESET
Active-Low Open-Drain or Push-Pull Reset Output. RESET
changes from high to low when the VCC input drops below the
selected reset threshold, MR is pulled low, or the watchdog triggers
a reset. RESET remains low for the reset timeout period after VCC
exceeds the device reset threshold, MR goes low to high, or the
watchdog triggers a reset.33RESET
Active-High Push-Pull Reset Output. RESET changes from low to
high when the VCC input drops below the selected reset threshold,
MR is pulled low, or the watchdog triggers a reset. RESET remains
high for the reset timeout period after VCC exceeds the device
reset threshold, MR goes low to high, or the watchdog triggers a
reset. 2222GNDGround334MR
Active-Low Manual Reset Input. Internal 50kΩ pullup to VCC.
Pull low to force a reset. Reset remains active as long as MR is
low and for the reset timeout period after MR goes high. Leave
unconnected or connect to VCC if unused.444WDI
Watchdog Input. If WDI remains high or low for longer than the
watchdog timeout period, the internal watchdog timer runs out
and a reset is triggered for the reset timeout period. The internal
watchdog timer clears whenever reset is asserted, the manual
reset is asserted, or WDI sees a rising or falling edge. If WDI is left
unconnected or is connected to a three-stated buffer output, the
watchdog feature is disabled.5555VCC Supply Voltage and Input for Reset Threshold Monitor
MAX6821/MAX6825Low-Voltage SOT23 µP Supervisors
with Manual Reset and Watchdog Timer
Pin Description
Disable the watchdog function by leaving WDI uncon-
nected or by three-stating the driver connected to WDI.
The watchdog input is internally driven low during the
first 7/8 of the watchdog timeout period and high for the
last 1/8 of the watchdog timeout period. When WDI is
left unconnected, this internal driver clears the 1.6s timer
every 1.4s. When WDI is three-stated or unconnected,
the maximum allowable leakage current is 10µA and the
maximum allowable load capacitance is 200pF.
Applications Information
Watchdog Input CurrentThe MAX6821/MAX6822/MAX6823/MAX6824 WDI inputs
are internally driven through a buffer and series resistor
from the watchdog timer (Figure 1). When WDI is left
unconnected, the watchdog timer is serviced within the
watchdog timeout period by a low-high-low pulse from
the counter chain. For minimum watchdog input current
(minimum overall power consumption), leave WDI low for
the majority of the watchdog timeout period, pulsing it low-
high-low once within the first 7/8 of the watchdog timeout
period to reset the watchdog timer. If WDI is externally
driven high for the majority of the timeout period, up to
160µA can flow into WDI.
Interfacing to µPs with
Bidirectional Reset PinsSince the RESET output on the MAX6822 is open drain,
it interfaces easily with µPs that have bidirectional reset
pins, such as the Motorola 68HC11. Connecting the µP
supervisor’s RESET output directly to the microcon-
troller’s RESET pin with a single pullup resistor allows
either device to assert reset (see Figure 4).
Negative-Going VCC TransientsThese supervisors are relatively immune to short-dura-
tion, negative-going VCC transients (glitches), which
usually do not require the entire system to shut down.
Figure 2. Reset Timing Diagram
Figure 1. Functional Diagram
VCC1V
tRD
VTHVTH
tRDRESET
GND
RESET
tRP
tRP
MAX6821–
MAX6825
VCC
VCC
WDI
(MAX6821–MAX6824)
1.26V
GND
RESET
(MAX6821/MAX6824/MAX6825)
RESET (MAX6822–MAX6825)
(MAX6821–MAX6823,
MAX6825)
RESET
GENERATOR
WATCHDOG
TIMER
WATCHDOG
TRANSITION
DETECTOR
MAX6821/MAX6825Low-Voltage SOT23 µP Supervisors
with Manual Reset and Watchdog Timer
