19-1867; Rev 2; 12/05
Dual Ultra-Low-Voltage SOT23 µP Supervisors
with Manual Reset and Watchdog Timer
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/BatteryPowered Equipment
Embedded Controllers
Intelligent Instruments
Automotive Systems
Critical µP Monitoring
Multivoltage Systems
Features
♦ 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 SOT23-6
MAX6827_UT-T
-40°C to +125°C
6 SOT23-6
MAX6828_UT-T
-40°C to +125°C
6 SOT23-6
MAX6829_ _UT-T
-40°C to +125°C
6 SOT23-6
MAX6830_ _UT-T
-40°C to +125°C
6 SOT23-6
MAX6831_ _UT-T
-40°C to +125°C
6 SOT23-6
†Insert the desired suffix letter (from Standard Versions table) into
Pin Configuration
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.
TOP VIEW
RESET(RESET) 1
GND 2
6
MAX6826–
MAX6831
VCC
Standard Versions Table*
MAX6826/MAX6827/MAX6828
5
RESET IN/VCC2
L
S
MR 3
4
WDI
R
Z
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.
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.
________________________________________________________________ Maxim Integrated Products
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
1
MAX6826–MAX6831
General Description
MAX6826–MAX6831
Dual Ultra-Low-Voltage SOT23 µP Supervisors
with Manual Reset and Watchdog Timer
ABSOLUTE MAXIMUM RATINGS
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, 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
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
CONDITIONS
1.0
5.5
1.2
5.5
VCC = +3.6V,
no load
MAX68_ _L
MAX68_ _M
MAX68_ _T
MAX68_ _S
VTH
MAX68_ _R
MAX68_ _Z
MAX68_ _Y
MAX68_ _W
MAX68_ _V
2
MAX
TA = -40°C to +125°C
TA = -40°C to +85°C
10
TA = -40°C to +125°C
7
TA = -40°C to +125°C
UNITS
V
20
30
TA = -40°C to +85°C
16
µA
25
VCC2 ≤ +2.5V
VCC2 Supply Current
VCC Reset Threshold
(VCC Falling)
TYP
TA = 0°C to +85°C
VCC = +5.5V,
no load
ICC
MIN
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
Dual Ultra-Low-Voltage SOT23 µP Supervisors
with Manual Reset and Watchdog Timer
(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)
ppm/°C
2 x VTH
mV
0.630
0.645
0.650
-25
+25
TA = -40°C to +125°C
-100
+100
20
VRSTIN = VRSTINTH to (VRSTINTH - 30mV)
tRP
VOL
140
TA = -40°C to +125°C
100
200
nA
µs
15
TA = -40°C to +85°C
V
mV
TA = -40°C to +85°C
VCC = VTH to (VTH - 100mV)
V
60
2.5
IRSTIN
UNITS
µs
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
_______________________________________________________________________________________
3
MAX6826–MAX6831
ELECTRICAL CHARACTERISTICS (continued)
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
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
VCC ≥ 1.8V, ISOURCE = 200µA, reset not asserted
0.8 ✕ VCC
TYP
MAX
VCC ≥ 3.15V, ISOURCE = 500µA, reset not asserted 0.8 ✕ VCC
UNITS
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
MR Glitch Rejection
µs
100
MR to Reset Delay
ns
200
MR Pullup Resistance
V
25
50
TA = -40°C to +85°C
1.12
1.6
TA = -40°C to +125°C
0.80
ns
75
kΩ
WATCHDOG INPUT
Watchdog Timeout Period
tWD
WDI Pulse Width (Note 2)
tWDI
WDI Input Voltage
WDI Input Current
50
0.3 ✕ VCC
0.7 ✕ VCC
WDI = VCC, time average
WDI = 0, time average
120
-20
-15
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.
4
s
ns
VIL
VIH
IWDI
2.4
2.60
_______________________________________________________________________________________
160
V
µA
Dual Ultra-Low-Voltage SOT23 µP Supervisors
with Manual Reset and Watchdog Timer
RESET TIMEOUT PERIOD
vs. TEMPERATURE
9
VCC = +1.8V, V VERSION
5
MAX6826 toc02
200
190
180
-40 -20
0
20
40
60
80
20
15
10
5
150
3
25
170
160
4
0
-40 -20
100 120
0
20
40
60
80
100 120
-40 -20
0
20
40
60
80
100 120
TEMPERATURE (°C)
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
MAX6826 toc04
2.0
1.9
1.04
RESET THRESHOLD (V)
1.8
1.7
1.6
1.5
1.4
1.3
1.2
1.02
1.00
0.98
0.96
120
100
80
RESET OCCURS
ABOVE CURVE
60
40
20
1.1
0.94
-40 -20
1.0
20
40
60
80
100 120
TEMPERATURE (°C)
0
0
20
40
60
80
100 120
TEMPERATURE (°C)
VRSTIN FALLING
VRSTIN = VRSTINTH - 30mV
20
15
10
20 40 60 80 100 120 140 160 180 200
RESET THRESHOLD OVERDRIVE (mV), VTH - VCC
VRSTIN TO RESET OUTPUT DELAY
vs. TEMPERATURE
25
0
MAXIMUM VRSTIN TRANSIENT DURATION
vs. RESET THRESHOLD OVERDRIVE
100
MAX6826 toc08
0
MAX6826 toc07
-40 -20
PROPAGATION DELAY (µs)
WATCHDOG TIMEOUT PERIOD (s)
210
MAX6826 toc06
6
VCC = +3.3V, S VERSION
220
VCC FALLING, VCC = VTH - 100mV
30
TRANSIENT DURATION (µs)
7
230
MAX6826 toc05
8
35
PROPAGATION DELAY (µs)
10
90
TRANSIENT DURATION (µs)
SUPPLY CURRENT (µA)
VCC = +5V, L VERSION
240
RESET TIMEOUT PERIOD (ms)
12
11
250
MAX6826 toc01
13
VCC TO RESET OUTPUT DELAY
vs. TEMPERATURE
MAX6826 toc03
SUPPLY CURRENT
vs. TEMPERATURE
80
70
60
50
40
RESET OCCURS
ABOVE CURVE
30
20
5
10
0
0
-40 -20
0
20
40
60
TEMPERATURE (°C)
80
100 120
0
20 40 60 80 100 120 140 160 180 200
RESET THRESHOLD OVERDRIVE (mV), VRSTINTH - VRSTIN
_______________________________________________________________________________________
5
MAX6826–MAX6831
Typical Operating Characteristics
(TA = +25°C, unless otherwise noted.)
Typical Operating Characteristics (continued)
(TA = +25°C, unless otherwise noted.)
MAX6826 toc09
2.92
VCC = +2.9V
0.300
VCC = +2.9V
2.90
2.88
0.250
MAX6826 toc10
VOLTAGE OUTPUT HIGH vs. ISOURCE
VOLTAGE OUTPUT LOW vs. ISINK
0.350
2.86
VOUT (V)
VOUT (V)
MAX6826–MAX6831
Dual Ultra-Low-Voltage SOT23 µP Supervisors
with Manual Reset and Watchdog Timer
0.200
0.150
2.84
2.82
2.80
0.010
2.78
0.005
2.76
2.74
0
0
1
2
3
4
5
6
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
7
ISOURCE (mA)
ISINK (mA)
Pin Description
PIN
MAX
6826
MAX
6827
1
MAX
6828
1
MAX
6829
1
1
MAX
6831
1
1
NAME
FUNCTION
RESET
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
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.
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
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.
2
2
2
2
2
2
GND
3
3
3
3
3
3
MR
Manual Reset Input, Active-Low, 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.
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
6
MAX
6830
4
4
4
4
4
Ground
_______________________________________________________________________________________
Dual Ultra-Low-Voltage SOT23 µP Supervisors
with Manual Reset and Watchdog Timer
PIN
MAX
6826
MAX
6827
MAX
6828
5
5
5
6
6
6
MAX
6829
MAX
6830
MAX
6831
NAME
FUNCTION
RESET
IN
Input for User Adjustable RESET IN Monitor. High-impedance input for
internal reset comparator. Connect this pin to an external resistor-divider
network to set the reset threshold voltage. 0.63V (typ) threshold.
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
_______________________________________________________________________________________
7
MAX6826–MAX6831
Pin Description (continued)
MAX6826–MAX6831
Dual Ultra-Low-Voltage SOT23 µP Supervisors
with Manual Reset and Watchdog Timer
VCC
MAX6829/MAX6830/MAX6831
RESET
OR
RESET
RESET TIMEOUT
DELAY GENERATOR
1.26V
0.63V
VCC2
VCC
MR
WATCHDOG
TRANSITION
DETECTOR
WDI
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 code-execution 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 MR
8
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
_______________________________________________________________________________________
Dual Ultra-Low-Voltage SOT23 µP Supervisors
with Manual Reset and Watchdog Timer
tRST
VCC
VCC
MAX6828
MAX6831 RESET
RESET*
tRP
tWD
RESET
tRP
RESET
GENERATOR
WDI
GND
*RESET IS THE INVERSE OF RESET.
µP
GND
Figure 6. Interfacing Open-Drain RESET to µPs with
Bidirectional Reset I/O
Figure 4. Watchdog Timing Relationship
the maximum allowable leakage current is 10µA and the
maximum allowable load capacitance is 200pF.
VMONITOR
R1
MAX6826
MAX6827
MAX6828
RSTIN
R2
VCC ≥ VRSTIN
Adjustable Reset Thresholds
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,
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 lowhigh-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 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
_______________________________________________________________________________________
9
MAX6826–MAX6831
VCC
MAX6826–MAX6831
Dual Ultra-Low-Voltage SOT23 µP Supervisors
with Manual Reset and Watchdog Timer
directly to the microcontroller’s RESET pin with a single
pullup resistor allows the device to assert a reset
(Figure 6).
Negative-Going VCC Transients
These supervisors are relatively immune to short-duration, negative-going V CC transients (glitches), which
usually do not require the entire system to shut down.
Resets are issued to the µP during power-up, powerdown, 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.
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-highlow. 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.
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.
START
SET WDI
HIGH
PROGRAM
CODE
SUBROUTINE OR
PROGRAM LOOP
SET WDI LOW
VCC
RETURN
Figure 8. Watchdog Flow Diagram
MAX6826
MAX6829
RESET
GND
R1
100kΩ
Figure 7. RESET Valid to VCC = Ground Circuit
10
______________________________________________________________________________________
Dual Ultra-Low-Voltage SOT23 µP Supervisors
with Manual Reset and Watchdog Timer
VCC THRESHOLD
RESET THRESHOLD (V)
VCC2 THRESHOLD
RESET THRESHOLD (V)
2.313
L
4.63
Z
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
E
0.833
D
0.788
V
1.58
Selector Guide
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
—
—
✔
✔
✔
✔
—
FUNCTION
Standard Versions
Table* (continued)
MAX6829/MAX6830/MAX6831
VCC
3.3V
Chip Information
TRANSISTOR COUNT: 750
PROCESS TECHNOLOGY: BiCMOS
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.
Typical Operating Circuit
VCC
CORE
SUPPLY
VCC2
I/O
SUPPLY
VCC
VCC2
RESET
MAX6829
MAX6830
MAX6831 WDI
MANUAL
RESET
MR
RESET
µP
I/O
GND
______________________________________________________________________________________
11
MAX6826–MAX6831
Threshold Suffix Guide
Package Information
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information,
go to www.maxim-ic.com/packages.)
6LSOT.EPS
MAX6826–MAX6831
Dual Ultra-Low-Voltage SOT23 µP Supervisors
with Manual Reset and Watchdog Timer
PACKAGE OUTLINE, SOT 6L BODY
21-0058
G
1
1
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
12
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