MAX6826-MAX6831
Dual Ultra-Low-Voltage SOT23 µP Supervisors
with Manual Reset and Watchdog Timer
General Description
The MAX6826–MAX6831 are ultra-low-voltage microprocessor (µP) supervisory circuits designed to monitor two
power supplies and have manual reset and watchdog
input functions. These devices assert a system reset
if any of the monitored supplies fall below the preprogrammed thresholds, and maintain reset for a minimum
timeout period after the supplies rise above the threshold.
Microprocessor supervisors significantly improve system
reliability and accuracy compared to separate ICs or
discrete components. These devices monitor primary
voltages from +1.8V to +5.0V and secondary voltages
from +0.9V to +2.5V. These devices are guaranteed to be
in the correct state for VCC down to +1.0V.
A variety of preprogrammed reset threshold voltages
are available (see the Threshold Suffix Guide). The
devices include manual reset and watchdog inputs.
The MAX6829/MAX6830/MAX6831 provide a factorytrimmed threshold to monitor a 2nd voltage down to
+0.9V. The MAX6826/MAX6829 have a push-pull
RESET, the MAX6827/MAX6830 have a push-pull
RESET and the MAX6828/MAX6831 have an open-drain
RESET. The MAX6826/MAX6827/MAX6828 have an
auxiliary monitor that allows user adjustable input to
monitor voltages down to +0.6V. see Selector Guide for
functions available.
Applications
●● Portable/Battery Powered Equipment
●● Embedded Controllers
●● Intelligent Instruments
●● Critical µP Monitoring
●● Multivoltage Systems
Pin Configuration
●● Monitor Primary VCC Supplies from +1.8V
to +5.0V and Secondary VCC2 Supplies
from +0.9V to +2.5V
●● User Adjustable RESET IN Down to +0.63V
(MAX6826/MAX6827/MAX6828)
●● 140ms (min) Reset Timeout Delay
●● 1.6s Watchdog Timeout Period
●● Manual Reset Input
●● Three Reset Output Options
Push-Pull RESET
Push-Pull RESET
Open-Drain RESET
●● Guaranteed Reset Valid Down to VCC = +1.0V
●● Immune to Short Negative VCC Transients
●● No External Components
●● Small 6-pin SOT23 Packages
Ordering Information
PART†
TEMP RANGE
PIN-PACKAGE
MAX6826_UT-T
-40°C to +125°C
6 SOT23
MAX6827_UT-T
-40°C to +125°C
6 SOT23
MAX6828_UT-T
-40°C to +125°C
6 SOT23
MAX6829_ _UT-T
-40°C to +125°C
6 SOT23
MAX6830_ _UT-T
-40°C to +125°C
6 SOT23
MAX6831_ _UT-T
-40°C to +125°C
6 SOT23
†Insert the desired suffix letter (from Standard versions table)
into the blanks to complete the part number.
Devices are available in both leaded and lead-free packaging.
Specify lead-free by replacing “-T” with “+T” when ordering.
Standard Versions Table*
TOP VIEW
MAX6826/MAX6827/MAX6828
RESET(RESET) 1
GND 2
6
MAX6826–
MAX6831
MR 3
VCC
5
RESET IN/VCC2
4
WDI
SOT23-6
(RESET) MAX6827/MAX6830 ONLY
RESET IN FOR MAX6826/MAX6827/MAX6828 ONLY
VCC2 FOR MAX6829/MAX6830/MAX6831 ONLY
Typical Operating Circuit, Threshold Suffix Guide, and
Selector Guide appear at end of data sheet.
19-1867; Rev 3; 7/14
Features
L
S
R
Z
V
*Samples are typically available for standard versions only. The
MAX6826/MAX6827/MAX6828 require a 2.5k minimum order
increment for all versions. Contact factory for availability.
Standard Versions Table continued at end of data sheet.
MAX6826-MAX6831
Dual Ultra-Low-Voltage SOT23 µP Supervisors with
Manual Reset and Watchdog Timer
Absolute Maximum Ratings
VCC, VCC2 to GND...............................................-0.3V to +6.0V
Open-Drain RESET...............................................-0.3V to +6.0V
Push-Pull RESET, RESET........................ -0.3V to (VCC + 0.3V)
MR, WDI, RESET IN................................. -0.3V to (VCC + 0.3V)
Input Current (VCC).............................................................20mA
Output Current (RESET, RESET).......................................20mA
Continuous Power Dissipation (TA = +70°C)
6-Pin SOT23 (derate 8.7mW/°C above +70°C)...........696mW
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
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.
Electrical Characteristics
(VCC = +4.5V to +5.5V for MAX68_ _L/M, VCC = +2.7V to +3.6V for MAX68_ _T/S/R, VCC = +2.1V to +2.75V for MAX68_ _Z/Y,
VCC = +1.53V to +2.0V for MAX68_ _W/V; TA = -40°C to +125°C, unless otherwise specified. Typical values are at TA = +25°C.) (Note 1)
PARAMETER
Operating Voltage Range
VCC Supply Current
MR and WDI Unconnected
SYMBOL
VCC
ICC
VCC2 Supply Current
CONDITIONS
TA = -40°C to +125°C
1.2
5.5
VCC = +5.5V,
no load
TA = -40°C to +85°C
VCC = +3.6V,
no load
TA = -40°C to +85°C
10
TA = -40°C to +125°C
7
TA = -40°C to +125°C
MAX68_ _T
MAX68_ _S
MAX68_ _R
MAX68_ _Z
MAX68_ _Y
MAX68_ _W
MAX68_ _V
UNITS
V
20
30
16
µA
25
VCC2 ≤ +2.5V
VTH
MAX
5.5
MAX68_ _M
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TYP
1.0
MAX68_ _L
VCC Reset Threshold
(VCC Falling)
MIN
TA = 0°C to +85°C
2
TA = -40°C to +85°C
4.50
4.63
4.75
TA = -40°C to +125°C
4.47
4.63
4.78
TA = -40°C to +85°C
4.25
4.38
4.50
TA = -40°C to +125°C
4.22
4.38
4.53
TA = -40°C to +85°C
3.00
3.08
3.15
TA = -40°C to +125°C
2.97
3.08
3.17
TA = -40°C to +85°C
2.85
2.93
3.00
TA = -40°C to +125°C
2.83
2.93
3.02
TA = -40°C to +85°C
2.55
2.63
2.70
TA = -40°C to +125°C
2.53
2.63
2.72
TA = -40°C to +85°C
2.25
2.32
2.38
TA = -40°C to +125°C
2.24
2.32
2.40
TA = -40°C to +85°C
2.12
2.19
2.25
TA = -40°C to +125°C
2.11
2.19
2.26
TA = -40°C to +85°C
1.62
1.67
1.71
TA = -40°C to +125°C
1.61
1.67
1.72
TA = -40°C to +85°C
1.52
1.58
1.62
µA
V
Maxim Integrated │ 2
MAX6826-MAX6831
Dual Ultra-Low-Voltage SOT23 µP Supervisors with
Manual Reset and Watchdog Timer
Electrical Characteristics (continued)
(VCC = +4.5V to +5.5V for MAX68_ _L/M, VCC = +2.7V to +3.6V for MAX68_ _T/S/R, VCC = +2.1V to +2.75V for MAX68_ _Z/Y,
VCC = +1.53V to +2.0V for MAX68_ _W/V; TA = -40°C to +125°C, unless otherwise specified. Typical values are at TA = +25°C.) (Note 1)
PARAMETER
SYMBOL
CONDITIONS
Z
Y
W
V
I
VCC2 Reset Threshold
VTH2
H
G
F
E
D
MIN
TYP
MAX
TA = -40°C to +85°C
2.244
2.313
2.381
TA = -40°C to +125°C
2.238
2.313
2.388
TA = -40°C to +85°C
2.119
2.188
2.257
TA = -40°C to +125°C
2.113
2.188
2.263
TA = -40°C to +85°C
1.615
1.665
1.715
TA = -40°C to +125°C
1.611
1.665
1.719
TA = -40°C to +85°C
1.525
1.575
1.625
TA = -40°C to +125°C
1.521
1.575
1.629
TA = -40°C to +85°C
1.346
1.388
1.429
TA = -40°C to +125°C
1.343
1.388
1.433
TA = -40°C to +85°C
1.271
1.313
1.354
TA = -40°C to +125°C
1.268
1.313
1.358
TA = -40°C to +85°C
1.077
1.110
1.143
TA = -40°C to +125°C
1.074
1.110
1.146
TA = -40°C to +85°C
1.017
1.050
1.083
TA = -40°C to +125°C
1.014
1.050
1.086
TA = -40°C to +85°C
0.808
0.833
0.858
TA = -40°C to +125°C
0.806
0.833
0.860
TA = -40°C to +85°C
0.762
0.788
0.813
TA = -40°C to +125°C
0.761
0.788
0.815
Reset Threshold Temperature
Coefficient
Reset Threshold Hysteresis
RESET IN Threshold
VRSTINTH VRSTINTH falling
TA = 0°C to +85°C
0.615
TA = -40°C to +125°C
0.610
RESET IN Hysteresis
RESET IN Input Current (Note 2)
VCC to Reset Output Delay
tRD
RESET IN to Reset Output Delay
Reset Timeout Period
RESET Output LOW
(Push-Pull or Open-Drain)
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tRP
VOL
V
60
ppm/°C
2 x VTH
mV
0.630
0.645
0.650
2.5
IRSTIN
UNITS
V
mV
TA = -40°C to +85°C
-25
+25
TA = -40°C to +125°C
-100
+100
nA
VCC = VTH to (VTH - 100mV)
20
µs
VRSTIN = VRSTINTH to (VRSTINTH - 30mV)
15
µs
TA = -40°C to +85°C
140
TA = -40°C to +125°C
100
200
280
320
VCC ≥ 1.0V, ISINK = 50µA, reset asserted,
TA = 0°C to +85°C
0.3
VCC ≥ 1.2V, ISINK = 100µA, reset asserted
0.3
VCC ≥ 2.55V, ISINK = 1.2mA, reset asserted
0.3
VCC ≥ 4.25V, ISINK = 3.2mA, reset asserted
0.4
ms
V
Maxim Integrated │ 3
MAX6826-MAX6831
Dual Ultra-Low-Voltage SOT23 µP Supervisors with
Manual Reset and Watchdog Timer
Electrical Characteristics (continued)
(VCC = +4.5V to +5.5V for MAX68_ _L/M, VCC = +2.7V to +3.6V for MAX68_ _T/S/R, VCC = +2.1V to +2.75V for MAX68_ _Z/Y,
VCC = +1.53V to +2.0V for MAX68_ _W/V; TA = -40°C to +125°C, unless otherwise specified. Typical values are at TA = +25°C.) (Note 1)
PARAMETER
SYMBOL
VCC ≥ 1.8V, ISOURCE = 200µA, reset not asserted
RESET Output HIGH
(Push-Pull Only)
VOH
Open-Drain RESET Output
Leakage Current (Note 1)
ILKG
RESET Output HIGH
(Push-Pull Only)
RESET Output LOW
(Push-Pull Only)
CONDITIONS
MIN
TYP
MAX
UNITS
0.8 × VCC
VCC ≥ 3.15V, ISOURCE = 500µA, reset not asserted 0.8 × VCC
V
VCC ≥ 4.75V, ISOURCE = 800µA, reset not asserted 0.8 × VCC
VOH
VOH
RESET not asserted
1.0
VCC ≥ 1.0V, ISOURCE = 1µA, reset asserted,
TA = 0°C to +85°C
0.8 × VCC
VCC ≥ 1.50V, ISOURCE = 100µA, reset asserted
0.8 × VCC
VCC ≥ 2.55V, ISOURCE = 500µA, reset asserted
0.8 × VCC
VCC ≥ 4.25V, ISOURCE = 800µA, reset asserted
0.8 × VCC
µA
V
VCC ≥ 1.8V, ISINK = 500µA, reset asserted
0.3
VCC ≥ 3.15V, ISINK = 1.2mA, reset asserted
0.3
VCC ≥ 4.75V, ISINK = 3.2mA, reset asserted
0.3
V
MANUAL RESET INPUT
MR Input voltage
0.3 × VCC
VIL
0.7 × VCC
VIH
MR Minimum Input Pulse
1
V
µs
MR Glitch Rejection
100
ns
MR to Reset Delay
200
ns
MR Pullup Resistance
25
50
75
TA = -40°C to +85°C
1.12
1.6
2.4
TA = -40°C to +125°C
0.80
kΩ
WATCHDOG INPUT
Watchdog Timeout Period
tWD
WDI Pulse Width (Note 2)
tWDI
WDI Input Voltage
WDI Input Current
2.60
50
ns
0.3 × VCC
VIL
0.7 × VCC
VIH
IWDI
WDI = VCC, time average
WDI = 0, time average
120
-20
s
-15
160
V
µA
Note 1: Over-temperature limits are guaranteed by design and not production tested. Devices tested at +25°C.
Note 2: Guaranteed by design and not production tested.
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Maxim Integrated │ 4
MAX6826-MAX6831
Dual Ultra-Low-Voltage SOT23 µP Supervisors with
Manual Reset and Watchdog Timer
Typical Operating Characteristics
(TA = +25°C, unless otherwise noted.)
10
9
VCC = +1.8V, V VERSION
4
-40 -20
0
20
40
60
170
20
15
10
5
-40 -20
0
20
40
60
0
80 100 120
-40 -20
0
20
40
60
80 100 120
TEMPERATURE (°C)
TEMPERATURE (C)
WATCHDOG TIMEOUT PERIOD
vs. TEMPERATURE
NORMALIZED RESET THRESHOLD
DELAY vs. TEMPERATURE
MAXIMUM VCC TRANSIENT DURATION
vs. RESET THRESHOLD OVERDRIVE
1.06
1.04
1.7
1.6
1.5
1.4
1.3
1.2
1.02
1.00
0.98
0.96
1.1
-40 -20
0
20
40
60
0.94
-40 -20
80 100 120
40
60
80 100 120
VRSTIN FALLING
VRSTIN = VRSTINTH - 30mV
100
80
RESET OCCURS
ABOVE CURVE
60
40
20
0
0
20 40 60 80 100 120 140 160 180 200
RESET THRESHOLD OVERDRIVE (mV), VTH - VCC
MAXIMUM VRSTIN TRANSIENT DURATION
vs. RESET THRESHOLD OVERDRIVE
VRSTIN TO RESET OUTPUT DELAY
vs. TEMPERATURE
MAX6826 toc07
PROPAGATION DELAY (µs)
20
20
TEMPERATURE (°C)
TEMPERATURE (°C)
25
0
120
MAX6826 toc06
1.8
MAX6826 toc03
25
TEMPERATURE (°C)
1.9
1.0
180
150
80 100 120
RESET THRESHOLD (V)
WATCHDOG TIMEOUT PERIOD (s)
2.0
190
160
MAX6826 toc04
3
200
VCC FALLING, VCC = VTH - 100mV
30
15
10
5
100
MAX6826 toc08
5
210
VCC TO RESET OUTPUT DELAY
vs. TEMPERATURE
35
TRANSIENT DURATION (µs)
6
220
MAX6826 toc05
7
VCC = +3.3V, S VERSION
230
90
TRANSIENT DURATION (µs)
8
MAX6826 toc02
VCC = +5V, L VERSION
240
RESET TIMEOUT PERIOD (ms)
SUPPLY CURRENT (µA)
12
11
250
MAX6826 toc01
13
RESET TIMEOUT PERIOD
vs. TEMPERATURE
PROPAGATION DELAY (µs)
SUPPLY CURRENT
vs. TEMPERATURE
80
70
60
50
40
RESET OCCURS
ABOVE CURVE
30
20
10
0
-40 -20
0
20
40
60
80 100 120
TEMPERATURE (C)
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0
0
20 40 60 80 100 120 140 160 180 200
RESET THRESHOLD OVERDRIVE (mV), VRSTINTH - VRSTIN
Maxim Integrated │ 5
MAX6826-MAX6831
Dual Ultra-Low-Voltage SOT23 µP Supervisors with
Manual Reset and Watchdog Timer
Typical Operating Characteristics (continued)
(TA = +25°C, unless otherwise noted.)
2.92
MAX6826 toc09
VCC = +2.9V
0.300
2.88
2.86
0.200
VOUT (V)
VOUT (V)
VCC = +2.9V
2.90
0.250
0.150
2.84
2.82
2.80
0.010
2.78
0.005
0
VOLTAGE OUTPUT HIGH vs. ISOURCE
MAX6826 toc10
VOLTAGE OUTPUT LOW vs. ISINK
0.350
2.76
0
1
2
3
4
5
6
2.74
7
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
ISINK (mA)
ISOURCE (mA)
Pin Description
PIN
MAX MAX
6826 6827
1
MAX
6828
1
MAX
6829
MAX
6830
1
1
MAX
6831
1
NAME
FUNCTION
Active-Low Open-Drain or Push-Pull Reset Output. RESET changes from high
to low when VCC1, VCC2, or RESET IN input drops below the selected reset
RESET threshold, MR is pulled low, or the watchdog triggers a reset. RESET remains
low for the reset timeout period after all voltages exceed the device reset
threshold, MR goes low to high, or the watchdog triggers a reset.
Active-High Push-Pull Reset Output. RESET changes from low to high when
VCC1, VCC2, or RESET IN input drops below the selected reset threshold, MR
RESET is pulled low, or the watchdog triggers a reset. RESET remains HIGH for the
reset timeout period after all voltages exceed the device reset threshold, MR
goes low to high, or the watchdog triggers a reset.
1
2
2
2
2
2
2
GND
3
3
3
3
3
3
MR
Manual-Reset Input, Active-Low, Internal 50kW 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.
WDI
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.
4
4
4
4
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4
4
Ground
Maxim Integrated │ 6
MAX6826-MAX6831
Dual Ultra-Low-Voltage SOT23 µP Supervisors with
Manual Reset and Watchdog Timer
Pin Description (continued)
PIN
MAX MAX
6826 6827
5
6
5
6
MAX
6828
MAX
6829
MAX
6830
MAX
6831
FUNCTION
RESET Input for User-Adjustable RESET IN Monitor. High-impedance input for
internal reset comparator. Connect this pin to an external resistor-divider
IN
network to set the reset threshold voltage. 0.63V (typ) threshold.
5
6
NAME
5
5
5
VCC2
Factory-Trimmed VCC2 Monitor. Connect this pin to a secondary powersupply voltage.
6
6
6
VCC
Supply Voltage. Input for primary reset threshold monitor.
VCC
MAX6826/MAX6827/MAX6828
RESET TIMEOUT
DELAY GENERATOR
RESET
OR
RESET
1.26V
0.63V
VCC
RESET IN
MR
WDI
WATCHDOG
TRANSITION
DETECTOR
WATCHDOG
TIMER
Figure 1. Functional Diagram of RESET IN
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Maxim Integrated │ 7
MAX6826-MAX6831
Dual Ultra-Low-Voltage SOT23 µP Supervisors with
Manual Reset and Watchdog Timer
MAX6829/MAX6830/MAX6831
VCC
RESET
OR
RESET
RESET TIMEOUT
DELAY GENERATOR
1.26V
0.63V
VCC2
VCC
MR
WDI
WATCHDOG
TRANSITION
DETECTOR
WATCHDOG
TIMER
Figure 2. Functional Diagram of VCC2
Detailed Description
RESET/RESET Output
A microprocessor’s (µP’s) reset input starts the
µP in a known state. The MAX6826–MAX6831 µP
supervisory circuits assert a reset to prevent codeexecution errors during power-up, power-down, and
brownout conditions. Whenever a monitored voltage falls
below the reset threshold, the reset output asserts low for
RESET and high for RESET. Once all monitored voltages
exceed their reset thresholds, an internal timer keeps
the reset output asserted for the specified reset timeout
period (tRP); after this interval, reset output returns to its
original state (Figure 3).
Manual-Reset Input
Many µP-based products require manual-reset
capability, allowing the operator, a test technician, or
external logic circuitry to initiate a reset. A logic low on
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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 driven with CMOS logic levels or with open-drain/collector
VCC
1V
VTH
VTH
1V
RESET
tRP
tRD
RESET
tRP
tRD
GND
Figure 3. Reset Timing Diagram
Maxim Integrated │ 8
MAX6826-MAX6831
VCC
RESET*
Dual Ultra-Low-Voltage SOT23 µP Supervisors with
Manual Reset and Watchdog Timer
VCC
tRST
MAX6828
MAX6831 RESET
tRP
tWD
VCC
RESET
tRP
RESET
GENERATOR
WDI
GND
*RESET IS THE INVERSE OF RESET.
Figure 4. Watchdog Timing Relationship
µP
GND
Figure 6. Interfacing Open-Drain RESET to µPs with
Bidirectional Reset I/O
Adjustable Reset Thresholds
VMONITOR
R1
MAX6826
MAX6827
MAX6828
RSTIN
R2
VCC ≥ VRSTIN
The MAX6826/MAX6827/MAX6828 provide a user
adjustable input to monitor a second voltage. The
threshold voltage at RSTIN is typically 0.63V. To monitor a voltage higher than 0.63V, connect a resistordivider to the circuit as shown in Figure 5. The
threshold at VMONITOR is:
R1 + R2
VMONITOR_TRIP = 0.63V
R2
Figure 5. Monitoring a Voltage
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 driven 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 Input
The watchdog circuit monitors 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 timeout
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 (Figure 4).
Disable the watchdog function by leaving WDI unconnected 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.
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Note that RSTIN is powered by VCC, and its voltage must
therefore remain lower than VCC.
Applications Information
Watchdog Input Current
The 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 watch-dog 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 Pins
Since the RESET output on the MAX6828/MAX6831
is open drain, these devices interface easily with µPs
that have bidirectional reset pins, such as the Motorola
68HC11. Connecting the µP supervisor’s RESET output
directly to the microcontroller’s RESET pin with a single
pullup resistor allows the device to assert a reset
(Figure 6).
Maxim Integrated │ 9
MAX6826-MAX6831
Dual Ultra-Low-Voltage SOT23 µP Supervisors with
Manual Reset and Watchdog Timer
Negative-Going VCC Transients
These supervisors are relatively immune to shortduration, negative-going VCC transients (glitches),
which usually do not require the entire system to shut
down. Resets are issued to the µP during power-up,
power-down, and brownout conditions. The Typical
Operating Characteristics show a graph of the Maximum
VCC Transient Duration vs. Reset Threshold Overdrive,
for which reset pulses are not generated. The graph
was produced using negative-going VCC pulses, starting at the standard monitored voltage and ending below
the reset threshold by the magnitude indicated (reset
threshold overdrive). The graph shows the maximum
pulse width that a negative-going VCC transient can
typically have without triggering a reset pulse. As the
amplitude of the transient increases (i.e., goes farther
below the reset threshold), the maximum allowable pulse
width decreases. Typically, a VCC transient that goes
100mV below the reset threshold and lasts for 20µs or
less will not trigger a reset pulse.
Ensuring a Valid RESET Output Down to
VCC = 0
The MAX6826–MAX6831 are guaranteed to operate
properly down to VCC = 1V. In applications that require
valid reset levels down to VCC = 0, a pulldown resistor to
active-low outputs (push/pull only, Figure 7) and a pullup
resistor to active-high outputs (push/pull only) will ensure
that the reset line is valid while the reset output can no
longer sink or source current. This scheme does not work
with the open-drain outputs of the MAX6828/MAX6831.
The resistor value used is not critical, but it must be small
enough not to load the reset output when VCC is above
the reset threshold. For falling slew rates greater than
1V/s, a 100kΩ is adequate.
Watchdog Software Considerations
One way to help the watchdog timer monitor software
execution more closely is to set and reset the watchdog
input at different points in the program, rather than pulsing
the watchdog input high-low-high or low-high-low. This
technique avoids a stuck loop, in which the watchdog
timer would continue to be reset inside the loop, keeping
the watchdog from timing out.
Figure 8 shows an example of a flow diagram where the
I/O driving the watchdog input is set high at the beginning of the program, set low at the beginning of every
subroutine or loop, then set high again when the program returns to the beginning. If the program should
hang in any subroutine, the problem would quickly be
corrected, since the I/O is continually set low and the
watchdog timer is allowed to time out, causing a reset
or interrupt to be issued. As described in the Watchdog
Input Current section, this scheme results in higher time
average WDI input current than does leaving WDI low
for the majority of the timeout period and periodically
pulsing it low-high-low.
START
SET WDI
HIGH
PROGRAM
CODE
SUBROUTINE OR
PROGRAM LOOP
SET WDI LOW
RETURN
VCC
Figure 8. Watchdog Flow Diagram
MAX6826
MAX6829
RESET
GND
R1
100kΩ
Figure 7. RESET Valid to VCC = Ground Circuit
www.maximintegrated.com
Maxim Integrated │ 10
MAX6826-MAX6831
Dual Ultra-Low-Voltage SOT23 µP Supervisors with
Manual Reset and Watchdog Timer
Threshold Suffix Guide
VCC THRESHOLD
RESET THRESHOLD (V)
VCC2 THRESHOLD
RESET THRESHOLD (V)
L
4.63
Z
2.313
M
4.38
Y
2.188
T
3.08
W
1.665
S
2.93
V
1.575
R
2.63
I
1.388
Z
2.32
H
1.313
Y
2.19
G
1.110
W
1.67
F
1.050
V
1.58
E
0.833
D
0.788
Selector Guide
FUNCTION
ACTIVE-LOW
RESET
ACTIVE-HIGH
RESET
OPEN-DRAIN
RESET
WATCHDOG
INPUT
MANUAL
RESET INPUT
FIXED VCC2
MONITOR
ADJUSTABLE
RESET
INPUT
MAX6826
✔
—
—
✔
✔
—
✔
MAX6827
—
✔
—
✔
✔
—
✔
MAX6828
—
—
✔
✔
✔
—
✔
MAX6829
✔
—
—
✔
✔
✔
—
MAX6830
—
✔
—
✔
✔
✔
—
MAX6831
—
—
✔
✔
✔
✔
—
Standard Versions Table* (continued)
MAX6829/MAX6830/MAX6831
VCC
3.3V
VCC2
2.5V
1.8V
—
TZ
—
—
2.5V
SV
ZW
—
1.8V
SH
YH
WI
1.5V
SF
YG
VF
1.2V
SD
YD
VD
0.9V
*Samples are typically available for standard versions only. For the MAX6829/MAX6830/MAX6831, standard versions require a 2.5k
minimum order increment, while nonstandard versions require a 10k minimum order increment and are not typically available in samples. Contact factory for availability.
www.maximintegrated.com
Maxim Integrated │ 11
MAX6826-MAX6831
Dual Ultra-Low-Voltage SOT23 µP Supervisors with
Manual Reset and Watchdog Timer
Typical Operating Circuit
Chip Information
TRANSISTOR COUNT: 750
PROCESS TECHNOLOGY: BiCMOS
VCC
CORE
I/O
SUPPLY SUPPLY
VCC2
VCC2
VCC
RESET
MAX6829
MAX6830
MAX6831
MANUAL
RESET
MR
www.maximintegrated.com
GND
RESET
µP
WDI
I/O
Package Information
For the latest package outline information and land patterns
(footprints), go to www.maximintegrated.com/packages. Note
that a “+”, “#”, or “-” in the package code indicates RoHS status
only. Package drawings may show a different suffix character, but
the drawing pertains to the package regardless of RoHS status.
PACKAGE
TYPE
PACKAGE
CODE
OUTLINE
NO.
LAND
PATTERN NO.
6 SOT
U6+1
21-0058
90-0175
Maxim Integrated │ 12
MAX6826-MAX6831
Dual Ultra-Low-Voltage SOT23 µP Supervisors with
Manual Reset and Watchdog Timer
Revision History
REVISION
NUMBER
REVISION
DATE
3
7/14
PAGES
CHANGED
DESCRIPTION
No /V OPNs; removed Automotive reference from Applications section
1
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim Integrated’s website at www.maximintegrated.com.
Maxim Integrated cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim Integrated product. No circuit patent licenses
are implied. Maxim Integrated reserves the right to change the circuitry and specifications without notice at any time. The parametric values (min and max limits)
shown in the Electrical Characteristics table are guaranteed. Other parametric values quoted in this data sheet are provided for guidance.
Maxim Integrated and the Maxim Integrated logo are trademarks of Maxim Integrated Products, Inc.
© 2014 Maxim Integrated Products, Inc. │ 13
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