General Description
The MAX6746–MAX6753 low-power microprocessor
(μP) supervisory circuits monitor single/dual system
supply voltages from 1.575V to 5V and provide maximum
adjustability for reset and watchdog functions. These
devices assert a reset signal whenever the VCC
supply voltage or RESET IN falls below its reset threshold
or when manual reset is pulled low. The reset output
remains asserted for the reset timeout period after VCC
and RESET IN rise above the reset threshold. The reset
function features immunity to power-supply transients.
The MAX6746–MAX6753 have ±2% factory-trimmed
reset threshold voltages in approximately 100mV
increments from 1.575V to 5.0V and/or adjustable reset
threshold voltages using external resistors.
The reset and watchdog delays are adjustable with
external capacitors. The MAX6746–MAX6751 contain
a watchdog select input that extends the watchdog
timeout period by 128x. The MAX6752/MAX6753 contain
a window watchdog timer that looks for activity outside an
expected window of operation.
The MAX6746–MAX6753 are available with a push-pull
or open-drain active-low RESET output. The MAX6746–
MAX6753 are available in an 8-pin SOT23 package and
are fully specified over the automotive temperature range
(-40°C to +125°C).
Applications
Medical Equipment
Automotive
Intelligent Instruments
Portable Equipment
Battery-Powered Computers/Controllers
Embedded Controllers
Critical μP Monitoring
Set-Top Boxes
Computers
Benets and Features
Configurable Reset and Watchdog Options Enables
Wide Variety of Applications
Factory-Set Reset Threshold Options from 1.575V
to 5V in ~100mV Increments
Adjustable Reset Threshold Options
Single/Dual Voltage Monitoring
Capacitor-Adjustable Reset Timeout
Capacitor-Adjustable Watchdog Timeout
Min/Max (Windowed) Watchdog Option
Manual-Reset Input Option
Push-Pull or Open-Drain RESET Output Options
3.7μA Supply Current Reduces System Power
Consumption
Integrated Power Supply Protection Increases
Robustness
Power-Supply Transient Immunity
Guaranteed RESET Valid for VCC ≥ 1V
8-Pin SOT23 Packages Saves Board Space
Selector Guide and Ordering Information appear at end of
data sheet.
19-2530; Rev 15; 1/17
MAX6748
MAX6749
MAX6750
MAX6751
RESET IN
GND
SRT
VCC
VCC
SWT
CSRT
CSWT
VIN
R1
R2
WDI
WDS
I/O
WDS = 0 FOR NORMAL MODE
WDS = VCC FOR EXTENDED MODE
MAX6749
MAX4751
µP
RESET RESET
Typical Operating Circuit
MAX6746–MAX6753 μP Reset Circuits with Capacitor-Adjustable
Reset/Watchdog Timeout Delay
VCC to GND...........................................................-0.3V to +6.0V
SRT, SWT, SET0, SET1, RESET IN, WDS, MR,
WDI, to GND......................................…-0.3V to (VCC + 0.3V)
RESET (Push-Pull) to GND....................…-0.3V to (VCC + 0.3V)
RESET (Open-Drain) to GND.............................…-0.3V to +6.0V
Input Current (All Pins).....................................................±20mA
Output Current (RESET) ...................................................±20mA
Continuous Power Dissipation (TA = +70°C)
8-Pin SOT23 (derate 8.9mW/°C above +70°C)...........714mW
Operating Temperature Range .........................-40°C to +125°C
Storage Temperature Range ............................-65°C to +150°C
Junction Temperature......................................................+150°C
Lead Temperature (soldering, 10s) .................................+300°C
Soldering Temperature (reflow) .......................................+260°C
(VCC = +1.2V to +5.5V, TA = TMIN to TMAX, unless otherwise specified. Typical values are at VCC = +5V and TA = +25°C.) (Note 1)
Absolute Maximum Ratings
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
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
Supply Voltage VCC
TA = 0°C to +125°C 1.0 5.5 V
TA = -40°C to 0°C 1.2 5.5
Supply Current ICC
VCC ≤ 5.5V 510
µAVCC ≤ 3.3V 4.2 9
VCC ≤ 2.0V 3.7 8
VCC Reset Threshold VTH See VTH
selection table TA = -40°C to +125°C VTH -
2% VTH +
2% V
Hysteresis VHYST 0.8 %
VCC Reset Threshold
(MAX6752AKA32 Only) TA = -40°C to +125°C 3.136 3.224 V
Hysteresis
(MAX6752AKA32 Only) VHYST 0.65 0.80 0.90 %
VCC to Reset Delay VCC falling from VTH + 100mV to VTH
-100mV at 1mV/µs 20 µs
Reset Timeout Period tRP
CSRT = 1500pF 5.692 7.590 9.487 ms
CSRT = 100pF 0.506
SRT Ramp Current IRAMP VSRT = 0 to 1.23V; VCC = 1.6V to 5V 200 250 300 nA
SRT Ramp Threshold VRAMP VCC = 1.6V to 5V (VRAMP rising) 1.173 1.235 1.297 V
Normal Watchdog Timeout Period
(MAX6746–MAX6751) tWD
CSWT = 1500pF 5.692 7.590 9.487 ms
CSWT = 100pF 0.506
Extended Watchdog Timeout
(MAX6746–MAX6751) tWD
CSWT = 1500pF 728.6 971.5 1214.4 ms
CSWT = 100pF 64.77
Slow Watchdog Period
(MAX6752/MAX6753) tWD2
CSWT = 1500pF 728.6 971.5 1214.4 ms
CSWT = 100pF 64.77
Fast Watchdog Timeout Period,
SET Ratio = 8,
(MAX6752/MAX6753) tWD1
CSWT = 1500pF 91.08 121.43 151.80 ms
CSWT = 100pF 8.09
Fast Watchdog Timeout Period,
SET Ratio = 16,
(MAX6752/MAX6753) tWD1
CSWT = 1500pF 45.53 60.71 75.89
ms
CSWT = 100pF 4.05
MAX6746–MAX6753 μP Reset Circuits with Capacitor-Adjustable
Reset/Watchdog Timeout Delay
www.maximintegrated.com Maxim Integrated
2
(VCC = +1.2V to +5.5V, TA = TMIN to TMAX, unless otherwise specified. Typical values are at VCC = +5V and TA = +25°C.) (Note 1)
Note 1: Production testing done at TA = +25°C. Over temperature limits are guaranteed by design.
Electrical Characteristics (continued)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
Fast Watchdog Timeout Period,
SET Ratio = 64,
(MAX6752/MAX6753) tWD1
CSWT = 1500pF 11.38 15.18 18.98
ms
CSWT = 100pF 1.01
Fast Watchdog Minimum Period
(MAX6752/MAX6753) 2000 ns
SWT Ramp Current IRAMP VSWT = 0 to 1.23V, VCC = 1.6V to 5V 200 250 300 nA
SWT Ramp Threshold VRAMP VCC = 1.6V to 5V (VRAMP rising) 1.173 1.235 1.297 V
RESET Output-Voltage Low
Open-Drain, Push-Pull
(Asserted)
VOL
VCC ≥ 1.0V, ISINK = 50µA 0.3
VVCC ≥ 2.7V, ISINK = 1.2mA 0.3
VCC 4.5V, ISINK = 3.2mA 0.4
RESET Output-Voltage High,
Push-Pull (Not Asserted) VOH
VCC ≥ 1.8V, ISOURCE = 200µA 0.8 x VCC
VVCC ≥ 2.25V, ISOURCE = 500µA 0.8 x VCC
VCC ≥ 4.5V, ISOURCE = 800µA 0.8 x VCC
RESET Output Leakage Current,
Open Drain ILKG VCC > VTH, reset not asserted,
VRESET = 5.5V 1.0 µA
DIGITAL INPUTS (MR, SET0, SET1, WDI, WDS)
Input Logic Levels
VIL VCC 4.0V 0.8
V
VIH 2.4
VIL VCC < 4.0V 0.3 x VCC
VIH 0.7 x VCC
MR Minimum Pulse Width 1µs
MR Glitch Rejection 100 ns
MR-to-RESET Delay 200 ns
MR Pullup Resistance Pullup to VCC 12 20 28 kΩ
WDI Minimum Pulse Width 300 ns
RESET IN
RESET IN Threshold VRESET IN TA = -40°C to +125°C 1.216 1.235 1.254 V
RESET IN Leakage Current IRESET IN -50 ±1+50 nA
RESET IN to RESET Delay RESET IN falling at 1mV/µs 20 µs
MAX6746–MAX6753 μP Reset Circuits with Capacitor-Adjustable
Reset/Watchdog Timeout Delay
www.maximintegrated.com Maxim Integrated
3
(VCC = +5V, TA = +25°C, unless otherwise noted.)
Typical Operating Characteristics
WATCHDOG TIMEOUT PERIOD vs. CSWT
MAX6746 toc02
CSWT (pF)
WATCHDOG TIMEOUT PERIOD (ms)
10,0001000
1
10
100
1000
10,000
100,000
0.1
100
100,000
MAX6746–MAX6751
EXTENDED MODE
NORMAL MODE
SUPPLY CURRENT
vs. SUPPLY VOLTAGE
MAX6746 toc03
SUPPLY VOLTAGE (V)
SUPPLY CURRENT (µA)
5432
2
1
3
4
5
6
0
1 6
NORMALIZED RESET TIMEOUT PERIOD
vs. TEMPERATURE
MAX6746 toc04
TEMPERATURE (°C)
NORMALIZED TIMEOUT PERIOD
1007550250-25
0.95
1.00
1.05
1.10
1.15
1.20
0.90
-50 125
CSRT = 100pF
CSRT = 1500pF
NORMALIZED WATCHDOG TIMEOUT PERIOD
vs. TEMPERATURE
MAX6746 toc05
TEMPERATURE (°C)
NORMALIZED TIMEOUT PERIOD
1007550250-25
0.95
0.90
0.85
1.00
1.05
1.10
1.15
1.20
0.80
-50 125
CSWT = 100pF
CSWT = 1500pF
MAXIMUM TRANSIENT DURATION
vs. RESET THRESHOLD OVERDRIVE
MAX6746 toc06
RESET THRESHOLD OVERDRIVE (mV)
TRANSIENT DURATION (µs)
800600400200
25
50
75
100
125
150
175
0
0 1000
RESET OCCURS
ABOVE THE CURVE
VTH = 2.92V
SUPPLY CURRENT
vs. TEMPERATURE
MAX6746 toc07
TEMPERATURE (°C)
SUPPLY CURRENT (µA)
1007525 500-25
1
2
3
4
5
6
0
-50 125
VCC = 3.3V
VCC = 1.8V
VCC = 5V
RESET TIMEOUT PERIOD vs. CSRT
MAX6746 toc01
CSRT (pF)
RESET TIMEOUT PERIOD (ms)
10,0001000
1
10
100
1000
0.1
100 100,000
NORMALIZED RESET IN THRESHOLD VOLTAGE
vs. TEMPERATURE
MAX6746 toc08
TEMPERATURE (°C)
NORMALIZED RESET THRESHOLD VOLTAGE
1007550250-25
0.994
0.992
0.996
1.000
0.998
1.004
1.002
1.008
1.006
1.010
0.990
-50 125
VCC = 5V
RESET IN THRESHOLD
vs. SUPPLY VOLTAGE
MAX6746 toc08b
SUPPLY VOLTAGE (V)
RESET IN THRESHOLD (V)
5432
1.236
1.237
1.238
1.239
1.240
1.235
1 6
Maxim Integrated
4
www.maximintegrated.com
MAX6746–MAX6753 μP Reset Circuits with Capacitor-Adjustable
Reset/Watchdog Timeout Delay
(VCC = +5V, TA = +25°C, unless otherwise noted.)
Typical Operating Characteristics (continued)
Pin Descriptions
( ) ARE FOR MAX6746 AND MAX6747 ONLY.
TOP VIEW
WDI
WDSGND
1
2
8
7
VCC
RESETSWT
SRT
RESET IN (MR)
3
4
6
5
MAX6746–
MAX6751
SOT23
+
WDI
SET1GND
1
2
8
7
V
CC
RESETSWT
SRT
SET0
3
4
6
5
MAX6752
MAX6753
SOT23
Pin Congurations
VCC TO RESET DELAY
vs. TEMPERATURE (VCC FALLING)
MAX6746 toc09
TEMPERATURE (°C)
VCC TO RESET DELAY (µs)
1007550250-25
25.4
25.8
26.2
26.6
27.0
25.0
-50 125
VCC FALLING AT 1mV/µs
RESET AND WATCHDOG
TIMEOUT PERIOD vs. SUPPLY VOLTAGE
MAX6746 toc10
VCC (V)
TIMEOUT PERIOD (ms)
5.55.04.0 4.52.5 3.0 3.52.0
0.44
0.48
0.52
0.56
0.60
0.40
1.5 6.0
CSWT = CSRT = 100pF
RESET AND WATCHING TIMEOUT
PERIOD vs. SUPPLY VOLTAGE
MAX6746 toc11
VCC (V)
TIMEOUT PERIOD (ms)
5.55.04.54.03.53.02.52.0
6.5
7.0
7.5
8.0
8.5
9.0
6.0
1.5 6.0
CSWT = CSRT = 1500pF
RESET
WATCHDOG
PIN
NAME FUNCTION
MAX6746
MAX6747
MAX6748–
MAX6751
MAX6752
MAX6753
1 MR Manual-Reset Input. Pull MR low to manually reset the device. Reset
remains asserted for the reset timeout period after MR is released.
1RESET IN Reset Input. High-impedance input to the adjustable reset comparator.
Connect RESET IN to the center point of an external resistor-divider to
set the threshold of the externally monitored voltage.
1 SET0 Logic Input. SET0 selects watchdog window ratio or disables the
watchdog timer. See Table 1.
Maxim Integrated
5
www.maximintegrated.com
MAX6746–MAX6753 μP Reset Circuits with Capacitor-Adjustable
Reset/Watchdog Timeout Delay
Pin Descriptions (continued)
PIN
NAME FUNCTION
MAX6746
MAX6747
MAX6748–
MAX6751
MAX6752
MAX6753
2 2 2 SWT
Watchdog Timeout Input.
MAX6746–MAX6751: Connect a capacitor between SWT and ground to
set the basic watchdog timeout period (tWD). Determine the period by
the formula tWD = 4.94 x 106 x CSWT with tWD in seconds and CSWT
in Farads. Extend the basic watchdog timeout period by using the WDS
input. Connect SWT to ground to disable the watchdog timer function.
MAX6752/MAX6753: Connect a capacitor between SWT and ground
to set the slow watchdog timeout period (tWD2). Determine the slow
watchdog period by the formula: tWD2 = 0.65 x 109 x CSWT with tWD2 in
seconds and CSWT in Farads. The fast watchdog timeout period is set
by pin strapping SET0 and SET1 (Connect SET0 high and SET1 low to
disable the watchdog timer function.) See Table 1.
333SRT Reset Timeout Input. Connect a capacitor from SRT to GND to select
the reset timeout period. Determine the period as follows: tRP = 4.94 x
106 x CSRT with tRP in seconds and CSRT in Farads.
444GND Ground
5 5 WDS
Watchdog Select Input. WDS selects the watchdog mode. Connect
WDS to ground to select normal mode and the watchdog timeout
period. Connect WDS to VCC to select extended mode, multiplying the
basic timeout period by a factor of 128. A change in the state of WDS
clears the watchdog timer.
5 SET1 Logic Input. SET1 selects the watchdog window ratio or disables the
watchdog timer. See Table 1.
666WDI
Watchdog Input.
MAX6746–MAX6751: A falling transition must occur on WDI within
the selected watchdog timeout period or a reset pulse occurs. The
watchdog timer clears when a transition occurs on WDI or whenever
RESET is asserted. Connect SWT to ground to disable the watchdog
timer function.
MAX6752/MAX6753: WDI falling transitions within periods shorter than
tWD1 or longer than tWD2 force RESET to assert low for the reset
timeout period. The watchdog timer begins to count after RESET is
deasserted. The watchdog timer clears when a valid transition occurs
on WDI or whenever RESET is asserted. Connect SET0 high and SET1
low to disable the watchdog timer function. See the Watchdog Timer
section.
777RESET
Push/Pull or Open-Drain Reset Output. RESET asserts whenever VCC
or RESET IN drops below the selected reset threshold voltage (VTH or
VRESET IN, respectively) or manual reset is pulled low. RESET remains
low for the reset timeout period after all reset conditions are deasserted,
and then goes high. The watchdog timer triggers a reset pulse (tRP)
whenever a watchdog fault occurs.
8 8 8 VCC Supply Voltage. VCC is the power-supply input and the input for xed
threshold VCC monitor.
MAX6746–MAX6753 μP Reset Circuits with Capacitor-Adjustable
Reset/Watchdog Timeout Delay
www.maximintegrated.com Maxim Integrated
6
Detailed Description
The MAX6746–MAX6753 assert a reset signal whenever
the VCC supply voltage or RESET IN falls below its reset
threshold. The reset output remains asserted for the reset
timeout period after VCC and RESET IN rise above its
respective reset threshold. A watchdog timer triggers a
reset pulse whenever a watchdog fault occurs.
The reset and watchdog delays are adjustable with
external capacitors. The MAX6746–MAX6751 contain a
watchdog select input that extends the watchdog timeout
period to 128x.
The MAX6752 and MAX6753 have a sophisticated watchdog
timer that detects when the processor is running outside
an expected window of operation. The watchdog signals a
fault when the input pulses arrive too early (faster that the
selected tWD1 timeout period) or too late (slower than the
selected tWD2 timeout period) (see Figure 1).
Reset Output
The reset output is typically connected to the reset input
of a μP. A μP’s reset input starts or restarts the μP in a
known state. The MAX6746–MAX6753 μP supervisory
circuits provide the reset logic to prevent code-execution
errors during power-up, power-down, and brownout conditions
(see the Typical Operating Circuit). RESET changes from
high to low whenever the monitored voltage, RESET
IN and/or VCC drop below the reset threshold voltages.
Once VRESET IN and/or VCC exceeds its respective reset
threshold voltage(s), RESET remains low for the reset
timeout period, then goes high.
RESET is guaranteed to be in the correct logic
state for VCC greater than 1V. For applications
requiring valid reset logic when VCC is less than 1V,
see the Ensuring a Valid RESET Down to VCC = 0V
(Push-Pull RESET) section.
RESET IN Threshold
The MAX6748–MAX6751 monitor the voltage on RESET
IN using an adjustable reset threshold (VRESET IN) set
with an external resistor voltage-divider (Figure 2). Use
the following formula to calculate the externally monitored
voltage (VMON_TH):
VMON_TH = VRESET IN x (R1 + R2)/R2
Figure 1. MAX6752/MAX6753 Detailed Watchdog Input Timing Relationship
Figure 2. Calculating the Monitored Threshold Voltage
(VMON_TH)
WDI CONDITION 1
WDI CONDITION 2
WDI CONDITION 3
GUARANTEED TO
NOT ASSERT
RESET
GUARANTEED TO
ASSERT
RESET
tWD1 (MIN) tWD1 (MAX)
*UNDETERMINED *UNDETERMINED
FAST FAULT
NORMAL OPERATION
SLOW FAULT
*UNDETERMINED STATES MAY OR MAY NOT GENERATE A FAULT CONDITION
GUARANTEED
TO ASSERT
RESET
tWD2 (MIN) tWD2 (MAX)
MAX6748
MAX6749
MAX6750
MAX6751
RESET IN
GND
VCC
VCC
VMON_TH
VMON_TH = 1.235 x (R1 + R2) / R2
R1
R2
MAX6746–MAX6753 μP Reset Circuits with Capacitor-Adjustable
Reset/Watchdog Timeout Delay
www.maximintegrated.com Maxim Integrated
7
where VMON_TH is the desired reset threshold voltage
and VTH is the reset input threshold (1.235V). Resistors
R1 and R2 can have very high values to minimize
current consumption due to low leakage currents. Set R2
to some conveniently high value (500kΩ, for example)
and calculate R1 based on the desired reset threshold
voltage, using the following formula:
R1 = R2 x (VMON_TH/VRESET IN - 1) (Ω)
The MAX6748 and MAX6749 do not monitor VCC
supply voltage; therefore, VCC must be greater than
1.5V to guarantee RESET IN threshold accuracy and
timing performance. The MAX6748 and MAX6749 can be
configured to monitor VCC voltage by connecting VCC to
VMON_TH.
Dual-Voltage Monitoring (MAX6750/MAX6751)
The MAX6750 and MAX6751 contain both factory-trimmed
threshold voltages and an adjustable reset threshold input,
allowing the monitoring of two voltages, V
CC
and V
MON_
TH
(see Figure 2). RESET is asserted when either of the
voltages fall below its respective threshold voltages.
Manual Reset (MAX6746/MAX6747)
Many μP-based products require manual-reset capability
to allow an operator or external logic circuitry to initiate a
reset. The manual-reset input (MR) can connect directly
to a switch without an external pullup resistor or debouncing
network. MR is internally pulled up to VCC and, therefore,
can be left unconnected if unused.
MR is designed to reject fast, falling transients (typically
100ns pulses) and must be held low for a minimum of
1μs to assert the reset output. A 0.1μF capacitor from MR
to ground provides additional noise immunity. After MR
transitions from low to high, reset remains asserted for the
duration of the reset timeout period.
A manual-reset option can easily be implemented with
the MAX6748–MAX6751 by connecting a normally open
momentary switch in parallel with R2 (Figure 3). When
the switch is closed, the voltage on RESET IN goes to
zero, initiating a reset. Similar to the MAX6746/MAX6747
manual reset, reset remains asserted while the voltage at
RESET IN is zero and for the reset timeout period after
the switch is opened.
Figure 4a. Watchdog Timing Diagram, WDS = GND
Figure 3. Adding an External Manual-Reset Function to the
MAX6748–MAX6751
VCC
WDI tWD tRP
RESET
NORMAL MODE (WDS = GND)
VCC
OV
OV
MAX6748
MAX6749
MAX6750
MAX6751
RESET IN
GND
VCC
VCC
VMON_TH
R1
R2
MAX6746–MAX6753 μP Reset Circuits with Capacitor-Adjustable
Reset/Watchdog Timeout Delay
www.maximintegrated.com Maxim Integrated
8
Watchdog Timer
MAX6746–MAX6751
The watchdog’s circuit monitors the μP’s activity. It the μP
does not toggle the watchdog input (WDI) within tWD (user-
selected), RESET asserts for the reset timeout period. The
internal watchdog timer is cleared by any event that asserts
RESET, by a falling transition at WDI (which can detect
pulses as short as 300ns), or by a transition at WDS. The
watchdog timer remains cleared while reset is asserted; as
soon as reset is released, the timer starts counting.
The MAX6746–MAX6751 feature two modes of watch-
dog operation: normal mode and extended mode. In
normal mode (Figure 4a), the watchdog timeout period
is determined by the value of the capacitor connected
between SWT and ground. In extended mode (Figure
4b), the watchdog timeout period is multiplied by 128. For
example, in extended mode, a 0.1μF capacitor gives a
watchdog timeout period of 65s (see the Extended-Mode
Watchdog Timeout Period vs. CSWT graph in the Typical
Operating Circuit). To disable the watchdog timer function,
connect SWT to ground.
MAX6752/MAX6753
The MAX6752 and MAX6753 have a windowed watchdog
timer that asserts RESET for the adjusted reset timeout
period when the watchdog recognizes a fast watchdog fault
(tWDI < tWD1), or a slow watchdog fault (period > tWD2).
The reset timeout period is adjusted independently of the
watchdog timeout period.
The slow watchdog period (tWD2) is calculated as follows:
tWD2 = 0.65 x 109 x CSWT
with tWD2 in seconds and CSWT in Farads.
The fast watchdog period (tWD1) is selectable as a ratio
from the slow watchdog fault period (tWD2). Select the
fast watchdog period by pin strapping SET0 and SET1,
where high is VCC and low is GND. Table 1 illustrates
the SET0 and SET1 configuration for the 8, 16, and 64
window ratio ( tWD2/tWD1).
For example, if CSWT is 1500pF, and SET0 and SET1 are
low, then tWD2 is 975ms (typ) and tWD1 is 122ms (typ).
RESET asserts if the watchdog input has two falling edges
too close to each other (faster than tWD1) (Figure 5a) or
falling edges that are too far apart (slower than tWD2)
(Figure 5b). Normal watchdog operation is displayed in
Figure 5c. The internal watchdog timer is cleared when
a WDI falling edge is detected within the valid watchdog
window or when RESET is deasserted. All WDI inputs are
ignored while RESET is asserted.
The watchdog timer begins to count after RESET is
deasserted. The watchdog timer clears and begins to
count after a valid WDI falling logic input. WDI falling
transitions within periods shorter than tWD1 or longer than
tWD2 force RESET to assert low for the reset timeout
period. WDI falling transitions within the tWD1 and tWD2
window do not assert RESET. WDI transitions between
tWD1(min) and tWD1(max) or tWD2(min) and tWD2(max)
are not guaranteed to assert or deassert RESET. To
guarantee that the window watchdog does not assert
RESET, strobe WDI between tWD1(max) and tWD2(min).
The watchdog timer is cleared when RESET is asserted
or after a falling transition on WDI, or after a state
change on SET0 or SET1. Disable the watchdog timer by
connecting SET0 high and SET1 low.
Figure 4b. Watchdog Timing Diagram, WDS = VCC
Table 1. Min/Max Watchdog Setting
SET0 SET1 RATIO
Low Low 8
Low High 16
High Low Watchdog Disabled
High High 64
tWD x 128 tRP
VCC
WDI
RESET
EXTENDED MODE (WDS = VCC)
VCC
OV
OV
MAX6746–MAX6753 μP Reset Circuits with Capacitor-Adjustable
Reset/Watchdog Timeout Delay
www.maximintegrated.com Maxim Integrated
9
Applications Information
Selecting Reset/Watchdog Timeout Capacitor
The reset timeout period is adjustable to accommodate a
variety of μP applications. Adjust the reset timeout period
(tRP) by connecting a capacitor (CSRT) between SRT and
ground. Calculate the reset timeout capacitor as follows:
CSRT = tRP/(4.94 x 106)
with tRP in seconds and CSRT in Farads.
The watchdog timeout period is adjustable to
accommodate a variety of μP applications. With this
feature, the watchdog timeout can be optimized for soft-
ware execution. The programmer can determine how
often the watchdog timer should be serviced. Adjust
the watchdog timeout period (tWD) by connecting a
specific value capacitor (CSWT) between SWT and GND.
For normal mode operation, calculate the watchdog
timeout capacitor as follows:
CSWT = tWD/(4.94 x 106)
with tWD in seconds and CSWT in Farads.
For the MAX6752 and MAX6753 windowed watchdog
function, calculate the slow watchdog period, tWD2 as
follows:
tWD2 = 0.65 x 109 x CSWT
CSRT and CSWT must be a low-leakage (< 10nA) type
capacitor. Ceramic capacitors are recommended.
Transient Immunity
In addition to issuing a reset to the μP during power-up,
power-down, and brownout conditions, these supervisors
are relatively immune to short-duration supply transients
(glitches). The Maximum Transient Duration vs. Reset
Threshold Overdrive graph in the Typical Operating
Characteristics shows this relationship.
The area below the curves of the graph is the region in
which these devices typically do not generate a reset
pulse. This graph was generated using a falling pulse
applied to VCC, starting above the actual reset threshold
(VTH) and ending below it by the magnitude indicated
(reset threshold overdrive). As the magnitude of the transient
increases (farther below the reset threshold), the maxi-
mum allowable pulse width decreases. Typically, a VCC
transient that goes 100mV below the reset threshold and
lasts 50μs or less does not cause a reset pulse to be
issued. For applications where the power supply to VCC
has high transient rates, dV/dt > 5V/50µS, an RC filter on
VCC is required. See Figure 8.
Figure 5. MAX6752/MAX6753 Window Watchdog Diagram
Figure 6. Interfacing to Other Voltage Levels
WDI
(a) FAST FAULT
(b) SLOW FAULT
WDI
RESET
(c) NORMAL OPERATION (NO PULSING, OUTPUT STAYS HIGH)
RESET
WDI
RESET
tWDI < tWD1 (MIN)
tWDI > tWD2 (MAX)
tWD1 (MAX) < tWDI < tWD2 (MIN)
MAX6747
MAX6749
MAX6451
MAX6753
GND
N
RESET RESET
5V
VCC
VCC
GND
3.3V
µP
100k
MAX6746–MAX6753 μP Reset Circuits with Capacitor-Adjustable
Reset/Watchdog Timeout Delay
www.maximintegrated.com Maxim Integrated
10
Interfacing to Other Voltages for
Logic Compatibility
The open-drain RESET output can be used to interface
to a μP with other logic levels. As shown in Figure 6, the
open-drain output can be connected to voltages from 0
to 6V.
Generally, the pullup resistor connected to RESET
connects to the supply voltage that is being monitored at
the IC’s VCC pin. However, some systems can use the
open-drain output to level-shift from the monitored supply
to reset circuitry powered by some other supply. Keep
in mind that as the supervisor’s VCC decreases towards
1V, so does the IC’s ability to sink current at RESET.
Also, with any pullup resistor, RESET is pulled high as
VCC decays toward zero. The voltage where this occurs
depends on the pullup resistor value and the voltage to
which it is connected.
Ensuring a Valid RESET Down to VCC = 0V
(Push-Pull RESET)
When VCC falls below 1V, RESET current sinking capabilities
decline drastically. The high-impedance CMOS logic
inputs connected to RESET can drift to undetermined
voltages. This presents no problems in most applications,
since most μPs and other circuitry do not operate with
VCC below 1V.
In those applications where RESET must be valid down to
0V, add a pulldown resistor between RESET and GND for
the MAX6746/MAX6748/MAX6750/MAX6752 push/pull
outputs. The resistor sinks any stray leakage currents,
holding RESET low (Figure 7). The value of the pulldown
resistor is not critical; 100kΩ is large enough not to load
RESET and small enough to pull RESET to ground. The
external pulldown cannot be used with the open-drain
reset outputs.
Figure 7. Ensuring RESET Valid to VCC = 0V Figure 8. Application Circuit for High-Input Voltage Transient
Applications
MAX6746
MAX6748
MAX6450
MAX6752
GND
RESET
VCC
VCC
100k
MAX6753
RESET
V
CC
GND
100
1µF
3.3V
MAX6746–MAX6753 μP Reset Circuits with Capacitor-Adjustable
Reset/Watchdog Timeout Delay
www.maximintegrated.com Maxim Integrated
11
Table 2. Reset Threshold Voltage Suffix
(TA = -40°C to +125°C)
Table 3. Standard Version Table
Note: Standard versions are shown in bold. There is a 2500-piece
minimum order increment for standard versions.
Sample stock is typically held on standard versions only.
Nonstandard versions require a minimum order increment
of 10,000 pieces. Contact factory for availability
SUFFIX MIN TYP MAX
50 4.900 5.000 5.100
49 4.802 4.900 4.998
48 4.704 4.800 4.896
47 4.606 4.700 4.794
46 4.533 4.625 4.718
45 4.410 4.500 4.590
44 4.288 4.375 4.463
43 4.214 4.300 4.386
42 4.116 4.200 4.284
41 4.018 4.100 4.182
40 3.920 4.000 4.080
39 3.822 3.900 3.978
38 3.724 3.800 3.876
37 3.626 3.700 3.774
36 3.528 3.600 3.672
35 3.430 3.500 3.570
34 3.332 3.400 3.468
33 3.234 3.300 3.366
32 3.136 3.200 3.264
32A
(MAX6752AKA32 Only) 3.136 3.200 3.224
31 3.014 3.075 3.137
30 2.940 3.000 3.060
29 2.867 2.925 2.984
28 2.744 2.800 2.856
27 2.646 2.700 2.754
26 2.573 2.625 2.678
25 2.450 2.500 2.550
24 2.352 2.400 2.448
23 2.267 2.313 2.359
22 2.144 2.188 2.232
21 2.058 2.100 2.142
20 1.960 2.000 2.040
19 1.862 1.900 1.938
18 1.764 1.800 1.836
17 1.632 1.665 1.698
16 1.544 1.575 1.607
PART TOP MARK
MAX6746KA16 AEDI
MAX6746KA23 AEDJ
MAX6746KA26 AEDK
MAX6746KA29 AALN
MAX6746KA46 AEDL
MAX6747KA16 AALO
MAX6747KA23 AEDM
MAX6747KA26 AEDN
MAX6747KA29 AEDO
MAX6747KA46 AEDP
MAX6748KA AALP
MAX6749KA AALQ
MAX6750KA16 AEDQ
MAX6750KA23 AALR
MAX6750KA26 AEDR
MAX6750KA29 AEDS
MAX6750KA46 AEDT
MAX6751KA16 AEDU
MAX6751KA23 AEDV
MAX6751KA26 AEDW
MAX6751KA29 AEDX
MAX6751KA46 AEDY
MAX6752KA16 AEDZ
MAX6752KA23 AEEA
MAX6752KA26 AALT
MAX6752KA29 AEEB
MAX6752KA46 AEEC
MAX6753KA16 AEED
MAX6753KA23 AEEE
MAX6753KA26 AEEF
MAX6753KA29 AEEG
MAX6753KA46 AEEH
MAX6746–MAX6753 μP Reset Circuits with Capacitor-Adjustable
Reset/Watchdog Timeout Delay
www.maximintegrated.com Maxim Integrated
12
Selector Guide
PART
FIXED VCC
RESET
THRESHOLD
ADJUSTABLE
RESET
THRESHOLD
STANDARD
WATCHDOG
TIMER
MIN/MAX
WATCHDOG
TIMER
PUSH/ PULL
RESET
OPEN-DRAIN
RESET
MANUAL-
RESET
INPUT
MAX6746 X X X X
MAX6747 X X X X
MAX6748 X X X
MAX6749 X X X
MAX6750 X X X X
MAX6751 X X X X
MAX6752 X X X
MAX6753 X X X
MAX6746–MAX6753 μP Reset Circuits with Capacitor-Adjustable
Reset/Watchdog Timeout Delay
www.maximintegrated.com Maxim Integrated
13
Note: “_ _” represents the two number suffix needed when order-
ing the reset threshold voltage value for the MAX6746/MAX6747
and MAX6750–MAX6753. The reset threshold
voltages are available in approximately 100mV increments. Table 2
contains the suffix and reset factory-trimmed voltages. All devices
are available in tape-and-reel only. There is a
2500-piece minimum order increment for standard versions (see
Table 3). Sample stock is typically held on standard
versions only. Nonstandard versions require a minimum order
increment of 10,000 pieces. Contact factory for availability.
Devices are available in both leaded and lead(Pb)-free packaging.
+Denotes a lead(Pb)-free/RoHS-compliant package.
T = Tape and reel.
/V denotes an automotive qualified part.
*Future product—contact factory for availability.
Chip Information
PROCESS: BiCMOS
PART TEMP RANGE PIN-PACKAGE
MAX6746KA_ _-T -40°C to +125°C 8 SOT23
MAX6746KA_ _+T -40°C to +125°C 8 SOT23
MAX6747KA_ _+T -40°C to +125°C 8 SOT23
MAX6746KA_ _/V+T -40°C to +125°C 8 SOT23
MAX6747KA_ _-T -40°C to +125°C 8 SOT23
MAX6747KA_ _/V+T -40°C to +125°C 8 SOT23
MAX6748KA+T -40°C to +125°C 8 SOT23
MAX6749KA+T -40°C to +125°C 8 SOT23
MAX6750KA_ _+T -40°C to +125°C 8 SOT23
MAX6750KA_ __/V+T -40°C to +125°C 8 SOT23
MAX6751KA_ _-T -40°C to +125°C 8 SOT23
MAX6751KA_ _+T -40°C to +125°C 8 SOT23
MAX6751KA_ _/V+T* -40°C to +125°C 8 SOT23
MAX6752KA_ _+T -40°C to +125°C 8 SOT23
MAX6752KA_ _/V+T* -40°C to +125°C 8 SOT23
MAX6752AKA32+T -40°C to +125°C 8 SOT23
MAX6752AKA32/V+T* -40°C to +125°C 8 SOT23
MAX6753KA_ _-T -40°C to +125°C 8 SOT23
MAX6753KA_ _+T -40°C to +125°C 8 SOT23
MAX6753KA_ _/V+T -40°C to +125°C 8 SOT23
PACKAGE
TYPE
PACKAGE
CODE
OUTLINE
NO.
LAND
PATTERN NO.
8 SOT23 K8+5, K8-5 21-0078 90-0176
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.
Ordering Information
MAX6746–MAX6753 μP Reset Circuits with Capacitor-Adjustable
Reset/Watchdog Timeout Delay
www.maximintegrated.com Maxim Integrated
14
Revision History
REVISION
NUMBER
REVISION
DATE DESCRIPTION PAGES
CHANGED
0 7/02 Initial release
312/05 Added the lead-free notation 1
49/10 Added the automotive version of the MAX6746 and the MAX6753 and
revised the Typical Operating Characteristics 1, 4
512/10 Added the automotive version of the MAX6750 1
64/11 Added the automotive version of the MAX6747 1
712/13 Added the automotive version of the MAX6751 1
8 2/14 Added a future product reference to MAX6751KA_ _ /V+T 1
9 5/14 Corrected typo 10
10 6/14 Added the automotive version of the MAX6752 1
11 9/15 Added MAX6752A to data sheet with new limits 2, 12, 14
12 12/15 Added lead-free part numbers to Ordering Information table and lead-free
package code to Package Information table 14
13 2/16 Added MAX6752AKA32+T to Ordering Information table 14
14 9/16 Updated tWD equation value in Pin Conguration table and Applications
Information section 6, 10
15 1/17 Added text to Transient Immunity section and added Figure 8 10, 11
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 specications 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. © 2017 Maxim Integrated Products, Inc.
15
MAX6746–MAX6753 μP Reset Circuits with Capacitor-Adjustable
Reset/Watchdog Timeout Delay
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.
Mouser Electronics
Authorized Distributor
Click to View Pricing, Inventory, Delivery & Lifecycle Information:
Maxim Integrated:
MAX6751KA16+T MAX6746KA29+T MAX6747KA29+T MAX6747KA46+T MAX6749KA+T MAX6750KA29+T
MAX6751KA29+T MAX6752KA46+T MAX6753KA46+T MAX6746KA16+T MAX6746KA23+T MAX6746KA26+T
MAX6746KA31+T MAX6747KA23+T MAX6747KA31+T MAX6748KA+T MAX6751KA+T MAX6751KA22+T
MAX6751KA26+T MAX6751KA31+T MAX6751KA46+T MAX6752KA29+T MAX6753KA29+T MAX6753KA29/V+T
MAX6751KA30/V+T MAX6752KA31+T MAX6747KA46/V+T MAX6751KA30+T MAX6751KA17/V+T MAX6747KA23+
MAX6747KA16+T MAX6747KA26+ MAX6750KA46+T MAX6753KA26+T MAX6751KA43+T MAX6753KA30/V+T
MAX6747KA33+T MAX6747KA31+ MAX6753KA16+T MAX6752KA16+T MAX6747KA30/V+T MAX6747KA26+T
MAX6753KA31+T MAX6750KA32/V+T MAX6746KA29/V+T MAX6753KA28/V+T MAX6751KA50/V+T
MAX6753KA42/V+T