General Description
The MAX6826–MAX6831 are ultra-low-voltage micro-
processor (µP) supervisory circuits designed to monitor
two power supplies and have manual reset and watch-
dog input functions. These devices assert a system reset
if any of the monitored supplies fall below the prepro-
grammed 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 dis-
crete components. These devices monitor primary volt-
ages 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 Threshold Suffix Guide). The devices
include manual reset and watchdog inputs. The
MAX6829/MAX6830/MAX6831 provide a factory-
trimmed 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 aux-
iliary monitor that allows user adjustable input to monitor
voltages down to +0.6V. See Selector Guide for func-
tions available.
________________________Applications
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
MAX6826–MAX6831
Dual Ultra-Low-Voltage SOT23 µP Supervisors
with Manual Reset and Watchdog Timer
________________________________________________________________ Maxim Integrated Products 1
GND
WDIMR
16VCC
5RESET IN/VCC2
RESET(RESET)
(RESET) MAX6827/MAX6830 ONLY
RESET IN FOR MAX6826/MAX6827/MAX6828 ONLY
VCC2 FOR MAX6829/MAX6830/MAX6831 ONLY
MAX6826–
MAX6831
SOT23-6
TOP VIEW
2
34
Pin Configuration
19-1867; Rev 1; 1/02
Ordering Information
Standard Versions Table*
†Insert the desired suffix letter (from Standard Versions table) into
the blanks to complete the part number.
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
M AX6831_ _UT-T -40°C to +125°C 6 SOT23-6
MAX6826/MAX6827/MAX6828
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.
Portable/Battery-
Powered Equipment
Embedded Controllers
Intelligent Instruments
Automotive Systems
Critical µP Monitoring
Multivoltage Systems
Typical Operating Circuit appears at end of data sheet.
Threshold Suffix Guide appears at end of data sheet. Selector Guide appears at end of data sheet.
Standard Versions Table continued at end of data sheet.
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.
MAX6826–MAX6831
Dual Ultra-Low-Voltage SOT23 µP Supervisors
with Manual Reset and Watchdog Timer
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
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)
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.
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
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
TA = 0°C to +85°C 1.0 5.5
Operating Voltage Range VCC TA = -40°C to +125°C 1.2 5.5 V
TA = -40°C to +85°C1020
VCC = +5.5V,
no load TA = -40°C to +125°C30
TA = -40°C to +85°C716
VCC Supply Current
MR and WDI Unconnected ICC VCC = +3.6V,
no load TA = -40°C to +125°C25
µA
VCC2 Supply Current VCC2 ≤ +2.5V 2µA
TA = -40°C to +85°C 4.50 4.63 4.75
MAX68_ _L TA = -40°C to +125°C 4.47 4.63 4.78
TA = -40°C to +85°C 4.25 4.38 4.50
MAX68_ _M TA = -40°C to +125°C 4.22 4.38 4.53
TA = -40°C to +85°C 3.00 3.08 3.15
MAX68_ _T TA = -40°C to +125°C 2.97 3.08 3.17
TA = -40°C to +85°C 2.85 2.93 3.00
MAX68_ _S TA = -40°C to +125°C 2.83 2.93 3.02
TA = -40°C to +85°C 2.55 2.63 2.70
MAX68_ _R TA = -40°C to +125°C 2.53 2.63 2.72
TA = -40°C to +85°C 2.25 2.32 2.38
MAX68_ _Z TA = -40°C to +125°C 2.24 2.32 2.40
TA = -40°C to +85°C 2.12 2.19 2.25
MAX68_ _Y TA = -40°C to +125°C 2.11 2.19 2.26
TA = -40°C to +85°C 1.62 1.67 1.71
MAX68_ _W TA = -40°C to +125°C 1.61 1.67 1.72
VCC Reset Threshold
(VCC Falling) VTH
MAX68_ _V TA = -40°C to +85°C 1.52 1.58 1.62
V
MAX6826–MAX6831
Dual Ultra-Low-Voltage SOT23 µP Supervisors
with Manual Reset and Watchdog Timer
_______________________________________________________________________________________ 3
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 MIN TYP MAX UNITS
TA = -40°C to +85°C 2.244 2.313 2.381
ZTA = -40°C to +125°C 2.238 2.313 2.388
TA = -40°C to +85°C 2.119 2.188 2.257
YTA = -40°C to +125°C 2.113 2.188 2.263
TA = -40°C to +85°C 1.615 1.665 1.715
WTA = -40°C to +125°C 1.611 1.665 1.719
TA = -40°C to +85°C 1.525 1.575 1.625
VTA = -40°C to +125°C 1.521 1.575 1.629
TA = -40°C to +85°C 1.346 1.388 1.429
ITA = -40°C to +125°C 1.343 1.388 1.433
TA = -40°C to +85°C 1.271 1.313 1.354
HTA = -40°C to +125°C 1.268 1.313 1.358
TA = -40°C to +85°C 1.077 1.110 1.143
GTA = -40°C to +125°C 1.074 1.110 1.146
TA = -40°C to +85°C 1.017 1.050 1.083
FTA = -40°C to +125°C 1.014 1.050 1.086
TA = -40°C to +85°C 0.808 0.833 0.858
ETA = -40°C to +125°C 0.806 0.833 0.860
TA = -40°C to +85°C 0.762 0.788 0.813
VCC2 Reset Threshold VTH2
DTA = -40°C to +125°C 0.761 0.788 0.815
V
Reset Threshold Temperature
Coefficient 60 ppm/°C
Reset Threshold Hysteresis 2 x VTH mV
TA = 0°C to +85°C 0.615 0.630 0.645
RESET IN Threshold V
RS T IN TH VRSTINTH falling TA = -40°C to +125°C 0.610 0.650 V
RESET IN Hysteresis 2.5 mV
TA = -40°C to +85°C -25 +25
RESET IN Input Current (Note 2) IRSTIN TA = -40°C to +125°C -100 +100 nA
VCC to Reset Output Delay tRD VCC = VTH to (VTH - 100mV) 20 µs
RESET IN to Reset Output Delay VRSTIN = VRSTINTH to (VRSTINTH - 30mV) 15 µs
TA = -40°C to +85°C 140 200 280
Reset Timeout Period tRP TA = -40°C to +125°C 100 320 ms
VCC ≥ 1.0V, ISINK = 50µA, reset asserted,
TA = 0°C to +85°C0.3
VCC ≥ 1.2V, ISINK = 100µA, reset asserted 0.3
VCC ≥ 2.55V, ISINK = 1.2mA, reset asserted 0.3
RESET Output LOW
(Push-Pull or Open-Drain) VOL
VCC ≥ 4.25V, ISINK = 3.2mA, reset asserted 0.4
V
MAX6826–MAX6831
Dual Ultra-Low-Voltage SOT23 µP Supervisors
with Manual Reset and Watchdog Timer
4 _______________________________________________________________________________________
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 MIN TYP MAX UNITS
V
C C
≥ 1.8V , IS OURC E
= 200µA, reset not asser ted 0.8
✕ V
C
C
V
C C
≥ 3.15V , IS OURC E
= 500µA, reset not asser ted 0.8
✕ V
C
C
RESET Output HIGH
(Push-Pull Only) VOH
V
C C
≥ 4.75V , IS OURC E
= 800µA, reset not asser ted 0.8
✕ V
C
C
V
Open-Drain RESET Output
Leakage Current (Note 1) ILKG RESET not asserted 1.0 µA
VCC ≥ 1.0V, IS OU RC E
= 1µA, reset asserted,
TA = 0°C to +85°C0.8 ✕ V
C C
V
C C
≥ 1.50V , IS OU RC E
= 100µA, r eset asser ted 0.8
✕ V
C C
V
C C
≥ 2.55V , IS OU RC E
= 500µA, r eset asser ted 0.8
✕ V
C C
RESET Output HIGH
(Push-Pull Only) VOH
V
C C
≥ 4.25V , IS OU RC E
= 800µA, r eset asser ted 0.8
✕ V
C C
V
V
C C
≥ 1.8V , IS IN K = 500µA, r eset asser ted 0.3
V
C C
≥ 3.15V , IS IN K = 1.2m A, r eset asser ted 0.3
RESET Output LOW
(Push-Pull Only) VOH
V
C C
≥ 4.75V , IS IN K = 3.2m A, r eset asser ted 0.3
V
MANUAL RESET INPUT
VIL 0.3 ✕ V
C C
MR Input voltage VIH 0.7 ✕ V
C C
V
MR Minimum Input Pulse 1µs
MR Glitch Rejection 100 ns
MR to Reset Delay 200 ns
MR Pullup Resistance 25 50 75 kΩ
WATCHDOG INPUT
TA = -40°C to +85°C 1.12 1.6 2.4
Watchdog Timeout Period tWD TA = -40°C to +125°C 0.80 2.60 s
WDI Pulse Width (Note 2) tWDI 50 ns
VIL 0.3 ✕ V
C C
WDI Input Voltage VIH 0.7 ✕ V
C C
V
WDI = VCC, time average 120 160
WDI Input Current IWDI WDI = 0, time average -20 -15 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.
MAX6826–MAX6831
Dual Ultra-Low-Voltage SOT23 µP Supervisors
with Manual Reset and Watchdog Timer
_______________________________________________________________________________________ 5
3
5
4
7
6
9
8
10
12
11
13
-40 0 20 40-20 60 80 100 120
SUPPLY CURRENT
vs. TEMPERATURE
MAX6826 toc01
TEMPERATURE (°C)
SUPPLY CURRENT (µA)
VCC = +5V, L VERSION
VCC = +3.3V, S VERSION
VCC = +1.8V, V VERSION
150
170
160
190
180
210
200
220
240
230
250
-40 0 20 40-20 60 80 100 120
RESET TIMEOUT PERIOD
vs. TEMPERATURE
MAX6826 toc02
TEMPERATURE (°C)
RESET TIMEOUT PERIOD (ms)
0
10
5
20
15
30
25
35
-40 0 20-20 40 60 80 100 120
VCC TO RESET OUTPUT DELAY
vs. TEMPERATURE
MAX6826 toc03
TEMPERATURE (°C)
PROPAGATION DELAY (µs)
VCC FALLING, VCC = VTH - 100mV
1.0
1.2
1.1
1.4
1.3
1.6
1.5
1.7
1.9
1.8
2.0
-40 0 20 40-20 60 80 100 120
WATCHDOG TIMEOUT PERIOD
vs. TEMPERATURE
MAX6826 toc04
TEMPERATURE (°C)
WATCHDOG TIMEOUT PERIOD (s)
0.94
0.96
1.00
0.98
1.04
1.02
1.06
-40 0 20-20 40 60 80 100 120
NORMALIZED RESET THRESHOLD
DELAY vs. TEMPERATURE
MAX6826 toc05
TEMPERATURE (°C)
RESET THRESHOLD (V)
0
60
40
20
80
100
120
0806020 40 100 120 140 160 180 200
MAXIMUM VCC TRANSIENT DURATION
vs. RESET THRESHOLD OVERDRIVE
MAX6826 toc06
RESET THRESHOLD OVERDRIVE (mV), VTH - VCC
TRANSIENT DURATION (µs)
RESET OCCURS
ABOVE CURVE
0
10
5
20
15
25
-40 0 20-20 40 60 80 100 120
VRSTIN TO RESET OUTPUT DELAY
vs. TEMPERATURE
MAX6826 toc07
TEMPERATURE (°C)
PROPAGATION DELAY (µs)
VRSTIN FALLING
VRSTIN = VRSTINTH - 30mV
0
40
30
20
10
50
60
70
80
90
100
0806020 40 100 120 140 160 180 200
MAXIMUM VRSTIN TRANSIENT DURATION
vs. RESET THRESHOLD OVERDRIVE
MAX6826 toc08
RESET THRESHOLD OVERDRIVE (mV), VRSTINTH - VRSTIN
TRANSIENT DURATION (µs)
RESET OCCURS
ABOVE CURVE
Typical Operating Characteristics
(TA = +25°C, unless otherwise noted.)
MAX6826–MAX6831
Dual Ultra-Low-Voltage SOT23 µP Supervisors
with Manual Reset and Watchdog Timer
6 _______________________________________________________________________________________
0
0.010
0.005
0.200
0.150
0.300
0.250
0.350
0231 4567
VOLTAGE OUTPUT LOW vs. ISINK
MAX6826 toc09
ISINK (mA)
VOUT (V)
VCC = +2.9V
Typical Operating Characteristics (continued)
(TA = +25°C, unless otherwise noted.)
2.74
2.78
2.76
2.82
2.80
2.84
2.86
2.90
2.88
2.92
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
VOLTAGE OUTPUT HIGH vs. ISOURCE
MAX6826 toc10
ISOURCE (mA)
VOUT (V)
VCC = +2.9V
Pin Description
PIN NUMBER
MAX
6826
MAX
6827
MAX
6828
MAX
6829
MAX
6830
MAX
6831
PIN
NAME FUNCTION
1 1 1 1 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.
1 1 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 Ground
3 3 3 3 3 3 MR
M anual Reset Inp ut, Acti ve- Low , Inter nal 50kΩ p ul l up to V
C C
. P ul l l ow to for ce a
r eset. Reset r em ai ns acti ve as l ong as M R i s l ow and for the r eset ti m eout p er i od
after M R g oes hi g h. Leave unconnected or connect to V
C C
, i f unused .
4 4 4 4 4 4 WDI
Watchd og Inp ut. If WD I r em ai ns hi g h or l ow for l ong er than the w atchd og ti m eout
p er i od , the i nter nal w atchd og ti m er r uns out and a r eset i s tr i g g er ed for the r eset
ti m eout p er i od . The i nter nal w atchd og ti m er cl ear s w henever r eset i s asser ted , the
m anual r eset i s asser ted , or WD I sees a r i si ng or fal l i ng ed g e. If WD I i s l eft
unconnected or i s connected to a thr ee- stated b uffer outp ut, the w atchd og featur e
i s d i sab l ed .
MAX6826–MAX6831
Dual Ultra-Low-Voltage SOT23 µP Supervisors
with Manual Reset and Watchdog Timer
_______________________________________________________________________________________ 7
Pin Description (continued)
PIN NUMBER
MAX
6826
MAX
6827
MAX
6828
MAX
6829
MAX
6830
MAX
6831
PIN
NAME FUNCTION
5 5 5
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 power-
supply voltage.
6 6 6 6 6 6 VCC Supply Voltage. Input for primary reset threshold monitor.
MAX6826/MAX6827/MAX6828
VCC
VCC
WDI
OR
RESET
RESET
MR
RESET TIMEOUT
DELAY GENERATOR
1.26V
0.63V
WATCHDOG
TIMER
WATCHDOG
TRANSITION
DETECTOR
RESET IN
Figure 1. Functional Diagram of RESET IN
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 condi-
tions. 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 capabil-
ity, allowing the operator, a test technician, or external
logic circuitry to initiate a reset. 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 50kΩpullup 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
MAX6826–MAX6831
Dual Ultra-Low-Voltage SOT23 µP Supervisors
with Manual Reset and Watchdog Timer
8 _______________________________________________________________________________________
MAX6829/MAX6830/MAX6831
VCC
VCC2 VCC
WDI
OR
RESET
RESET
MR
RESET TIMEOUT
DELAY GENERATOR
1.26V
0.63V
WATCHDOG
TIMER
WATCHDOG
TRANSITION
DETECTOR
Figure 2. Functional Diagram of VCC2
VCC
1V
1V
tRD
VTH VTH
tRD
RESET
GND
RESET
tRP
tRP
Figure 3. Reset Timing Diagram
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 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 peri-
od (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 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.
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 moni-
tor a voltage higher than 0.63V, connect a resistor-
divider to the circuit as shown in Figure 5. The
threshold at VMONITOR is:
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 con-
sumption), 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
VV
RR
R
MONITOR TRIP_ . =+
063 12
2
MAX6826–MAX6831
Dual Ultra-Low-Voltage SOT23 µP Supervisors
with Manual Reset and Watchdog Timer
_______________________________________________________________________________________ 9
Figure 5. Monitoring a Voltage
VMONITOR
R1
R2
VCC ≥ VRSTIN
RSTIN
MAX6826
MAX6827
MAX6828
VCC
tWD tRP
tRP
tRST
WDI
RESET*
*RESET IS THE INVERSE OF RESET.
Figure 4. Watchdog Timing Relationship
Figure 6. Interfacing Open-Drain
RESET
to µPs with
Bidirectional Reset I/O
MAX6828
MAX6831
RESET
GENERATOR
GND GND
VCC VCC
RESET RESET
µP
MAX6826–MAX6831
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-dura-
tion, 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 criti-
cal, 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 100kΩis 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 begin-
ning of the program, set low at the beginning of every
subroutine or loop, then set high again when the pro-
gram 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.
Dual Ultra-Low-Voltage SOT23 µP Supervisors
with Manual Reset and Watchdog Timer
10 ______________________________________________________________________________________
Figure 8. Watchdog Flow Diagram
START
SET WDI
HIGH
PROGRAM
CODE
SUBROUTINE OR
PROGRAM LOOP
SET WDI LOW
RETURN
MAX6826
MAX6829
VCC
R1
100kΩ
RESET
GND
Figure 7. RESET Valid to VCC = Ground Circuit
MAX6826–MAX6831
Dual Ultra-Low-Voltage SOT23 µP Supervisors
with Manual Reset and Watchdog Timer
______________________________________________________________________________________ 11
Typical Operating Circuit
MAX6829
MAX6830
MAX6831
µP
VCC
VCC
VCC2
VCC2
GND
MANUAL
RESET
RESET
I/O
CORE
SUPPLY
I/O
SUPPLY
RESET
MR
WDI
Chip Information
TRANSISTOR COUNT: 750
PROCESS TECHNOLOGY: BiCMOS
Standard Versions
Table* (continued)
MAX6829/MAX6830/MAX6831
VCC VCC2
3.3V 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
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
E 0.833
V 1.58 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 — — ✔ ✔ ✔ ✔ —
*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.
MAX6826–MAX6831
Dual Ultra-Low-Voltage SOT23 µP Supervisors
with Manual Reset and Watchdog Timer
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 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
© 2002 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.
Package Information
6LSOT.EPS
