19-2530; Rev 3; 12/05
µP Reset Circuits with Capacitor-Adjustable
Reset/Watchdog Timeout Delay
General Description
The MAX6746–MAX6753 low-power microprocessor
(µP) supervisory circuits monitor single/dual system
supply voltages from 1.575V to 5V and provide maxi-
mum adjustability for reset and watchdog functions.
These devices assert a reset signal whenever the V
CC
supply voltage or RESET IN falls below its reset thresh-
old or when manual reset is pulled low. The reset output
remains asserted for the reset timeout period after V
CC
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 incre-
ments 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 time-
out 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).
Features
♦
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
♦
Guaranteed
RESET
Valid for V
CC
≥
1V
♦
3.7µA Supply Current
♦
Push-Pull or Open-Drain
RESET
Output Options
♦
Power-Supply Transient Immunity
♦
Small 8-Pin SOT23 Packages
MAX6746–MAX6753
Ordering Information
PART
MAX6746KA_
_-T
MAX6747KA_
_-T
MAX6748KA-T
MAX6749KA-T
MAX6750KA_
_-T
MAX6751KA_
_-T
MAX6752KA_
_-T
MAX6753KA_
_-T
TEMP RANGE
-40°C to +125°C
-40°C to +125°C
-40°C to +125°C
-40°C to +125°C
-40°C to +125°C
-40°C to +125°C
-40°C to +125°C
-40°C to +125°C
PIN-PACKAGE
8 SOT23-8
8 SOT23-8
8 SOT23-8
8 SOT23-8
8 SOT23-8
8 SOT23-8
8 SOT23-8
8 SOT23-8
Applications
Medical Equipment
Automotive
Intelligent Instruments
Portable Equipment
Battery-Powered
Computers/Controllers
Embedded Controllers
Critical µP Monitoring
Set-Top Boxes
Computers
Pin Configurations
TOP VIEW
RESET IN (MR) 1
SWT 2
SRT
3
8
7
V
CC
RESET
WDI
WDS
MAX6746–
MAX6751
6
5
Note:
“_ _” represents the two number suffix needed when
ordering the reset threshold voltage value for the
MAX6746/MAX6747 and MAX6750–MAX6753. The reset
threshold voltages are available in approximately 100mV incre-
ments. 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 ver-
sions (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-free packaging.
Specify lead-free by replacing “-T” with “+T” when ordering.
GND 4
SOT23-8
( ) ARE FOR MAX6746 AND MAX6747 ONLY.
Selector Guide appears at end of data sheet.
Typical Operating Circuit appears at end of data sheet.
Pin Configurations continued at end of data sheet.
________________________________________________________________
Maxim Integrated Products
1
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.
µP Reset Circuits with Capacitor-Adjustable
Reset/Watchdog Timeout Delay
MAX6746–MAX6753
ABSOLUTE MAXIMUM RATINGS
V
CC
to GND ...........................................................-0.3V to +6.0V
SRT, SWT, SET0, SET1, RESET IN, WDS,
MR,
WDI, to GND .......................................…-0.3V to (V
CC
+ 0.3V)
RESET
(Push-Pull) to GND......................…-0.3V to (V
CC
+ 0.3V)
RESET
(Open Drain) to GND .............................…-0.3V to +6.0V
Input Current (All Pins) .....................................................±20mA
Output Current (RESET) ...................................................±20mA
Continuous Power Dissipation (T
A
= +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
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
(V
CC
= +1.2V to +5.5V, T
A
= T
MIN
to T
MAX
, unless otherwise specified. Typical values are at V
CC
= +5V and T
A
= +25°C.) (Note 1)
PARAMETER
Supply Voltage
SYMBOL
V
CC
CONDITIONS
T
A
= 0°C to +125°C
T
A
= -40°C to 0°C
V
CC
≤
5.5V
Supply Current
I
CC
V
CC
≤
3.3V
V
CC
≤
2.0V
V
CC
Reset Threshold
Hysteresis
V
CC
to Reset Delay
Reset Timeout Period
SRT Ramp Current
SRT Ramp Threshold
Normal Watchdog Timeout Period
(MAX6746–MAX6751)
Extended Watchdog Timeout
(MAX6746–MAX6751)
Slow Watchdog Period
(MAX6752/MAX6753)
Fast Watchdog Timeout Period,
SET Ratio = 8,
(MAX6752/MAX6753)
Fast Watchdog Timeout Period,
SET Ratio = 16,
(MAX6752/MAX6753)
t
RP
I
RAMP
V
RAMP
t
WD
t
WD
t
WD2
V
TH
V
HYST
V
CC
falling from V
TH
+ 100mV to V
TH
-
100mV at 1mV/µs
C
SRT
= 1500pF
C
SRT
= 100pF
V
SRT
= 0 to 1.23V; V
CC
= 1.6V to 5V
V
CC
= 1.6V to 5V (V
RAMP
rising)
C
SWT
= 1500pF
C
SWT
= 100pF
C
SWT
= 1500pF
C
SWT
= 100pF
C
SWT
= 1500pF
C
SWT
= 100pF
C
SWT
= 1500pF
t
WD1
C
SWT
= 100pF
C
SWT
= 1500pF
t
WD1
C
SWT
= 100pF
4.05
45.53
8.09
60.71
75.89
ms
91.08
728.6
728.6
200
1.173
5.692
5.692
See V
TH
selection table
TA = -40°C to+125°C
V
TH
-
2%
0.8
20
7.590
0.506
250
1.235
7.590
0.506
971.5
64.77
971.5
64.77
121.43
151.80
ms
1214.4
1214.4
300
1.297
9.487
9.487
MIN
1.0
1.2
5
4.2
3.7
TYP
MAX
5.5
5.5
10
9
8
V
TH
+
2%
V
%
µs
ms
nA
V
ms
ms
ms
µA
UNITS
V
2
_______________________________________________________________________________________
µP Reset Circuits with Capacitor-Adjustable
Reset/Watchdog Timeout Delay
ELECTRICAL CHARACTERISTICS (continued)
(V
CC
= +1.2V to +5.5V, T
A
= T
MIN
to T
MAX
, unless otherwise specified. Typical values are at V
CC
= +5V and T
A
= +25°C.) (Note 1)
PARAMETER
Fast Watchdog Timeout Period,
SET Ratio = 64,
(MAX6752/MAX6753)
Fast Watchdog Minimum Period
(MAX6752/MAX6753)
SWT Ramp Current
SWT Ramp Threshold
RESET
Output-Voltage LOW
Open-Drain, Push-Pull
(Asserted)
RESET
Output-Voltage HIGH,
Push-Pull (Not Asserted)
RESET
Output Leakage Current,
Open Drain
I
RAMP
V
RAMP
V
OL
V
SWT
= 0 to 1.23V, V
CC
= 1.6V to 5V
V
CC
= 1.6V to 5V (V
RAMP
rising)
V
CC
≥
1.0V, I
SINK
= 50µA
V
CC
≥
2.7V, I
SINK
= 1.2mA
V
CC
≥
4.5V, I
SINK
= 3.2mA
V
CC
≥
1.8V, I
SOURCE
= 200µA
V
OH
V
CC
≥
2.25V, I
SOURCE
= 500µA
V
CC
≥
4.5V, I
SOURCE
= 800µA
I
LKG
V
CC
> V
TH
, reset not asserted,
V
RESET
= 5.5V
0.8 x V
CC
0.8 x V
CC
0.8 x V
CC
1.0
µA
V
SYMBOL
t
WD1
C
SWT
= 100pF
2000
200
1.173
250
1.235
300
1.297
0.3
0.3
0.4
V
1.01
ns
nA
V
CONDITIONS
C
SWT
= 1500pF
MIN
11.38
TYP
15.18
MAX
18.98
ms
UNITS
MAX6746–MAX6753
DIGITAL INPUTS (MR, SET0, SET1, WDI, WDS)
V
IL
Input Logic Levels
V
IH
V
IL
V
IH
MR
Minimum Pulse Width
MR
Glitch Rejection
MR
to
RESET
Delay
MR
Pullup Resistance
WDI Minimum Pulse Width
RESET IN
RESET IN Threshold
RESET IN Leakage Current
RESET IN to
RESET
Delay
V
RESET IN
I
RESET IN
RESET IN falling at 1mV/µs
TA = -40°C to +125°C
1.216
-50
1.235
±1
20
1.254
+50
V
nA
µs
Pullup to V
CC
12
300
V
CC
≥
4.0V
V
CC
< 4.0V
0.7 x V
CC
1
100
200
20
28
µs
ns
ns
kΩ
ns
0.8
2.4
0.3 x V
CC
V
Note 1:
Production testing done at T
A
= +25°C. Over temperature limits are guaranteed by design.
_______________________________________________________________________________________
3
µP Reset Circuits with Capacitor-Adjustable
Reset/Watchdog Timeout Delay
MAX6746–MAX6753
Typical Operating Characteristics
(V
CC
= +5V, T
A
= +25°C, unless otherwise noted.)
SUPPLY CURRENT
vs. SUPPLY VOLTAGE
MAX6746 toc02
MAX6746 toc03
RESET TIMEOUT PERIOD vs. C
SRT
MAX6746 toc01
WATCHDOG TIMEOUT PERIOD vs. C
SWT
100,000
WATCHDOG TIMEOUT PERIOD (ms)
10,000
EXTENDED MODE
1000
100
10
1
0.1
NORMAL MODE
MAX6746–MAX6751
6
5
SUPPLY CURRENT (µA)
4
3
2
1
0
100
1000
C
SWT
(pF)
10,000
100,000
1
2
10,000
RESET TIMEOUT PERIOD (ms)
1000
100
10
1
0.1
100
1000
C
SRT
(pF)
10,000
100,000
3
4
5
6
SUPPLY VOLTAGE (V)
NORMALIZED RESET TIMEOUT PERIOD
vs. TEMPERATURE
MAX6746 toc04
NORMALIZED WATCHDOG TIMEOUT PERIOD
vs. TEMPERATURE
1.15
NORMALIZED TIMEOUT PERIOD
1.10
1.05
1.00
0.95
0.90
0.85
0.80
C
SWT
= 100pF
C
SWT
= 1500pF
MAX6746 toc05
MAXIMUM TRANSIENT DURATION
vs. RESET THRESHOLD OVERDRIVE
150
TRANSIENT DURATION (µs)
125
100
75
50
25
0
V
TH
= 2.92V
0
200
400
600
800
1000
RESET OCCURS
ABOVE THE CURVE
MAX6746 toc06
1.20
NORMALIZED TIMEOUT PERIOD
1.15
1.10
C
SRT
= 100pF
1.05
1.00
0.95
0.90
-50
-25
0
25
50
75
100
1.20
175
C
SRT
= 1500pF
125
-50
-25
0
25
50
75
100
125
TEMPERATURE (°C)
TEMPERATURE (°C)
RESET THRESHOLD OVERDRIVE (mV)
SUPPLY CURRENT
vs. TEMPERATURE
MAX6746 toc07
NORMALIZED RESET IN THRESHOLD VOLTAGE
vs. TEMPERATURE
MAX6746 toc08
RESET IN THRESHOLD
vs. SUPPLY VOLTAGE
MAX6746 toc08b
NORMALIZED RESET THRESHOLD VOLTAGE
6
5
SUPPLY CURRENT (µA)
4
3
V
CC
= 3.3V
2
1
0
-50
-25
0
25
50
75
100
V
CC
= 1.8V
V
CC
= 5V
1.010
1.008
1.006
1.004
1.002
1.000
0.998
0.996
0.994
0.992
0.990
V
CC
= 5V
1.240
RESET IN THRESHOLD (V)
-50
-25
0
25
50
75
100
125
1.239
1.238
1.237
1.236
1.235
1
2
3
4
5
6
TEMPERATURE (°C)
SUPPLY VOLTAGE (V)
125
TEMPERATURE (°C)
4
_______________________________________________________________________________________
µP Reset Circuits with Capacitor-Adjustable
Reset/Watchdog Timeout Delay
MAX6746–MAX6753
Typical Operating Characteristics (continued)
(V
CC
= +5V, T
A
= +25°C, unless otherwise noted.)
V
CC
TO RESET DELAY
vs. TEMPERATURE (V
CC
FALLING)
MAX6746 toc09
RESET AND WATCHDOG
TIMEOUT PERIOD vs. SUPPLY VOLTAGE
C
SWT
= C
SRT
= 100pF
MAX6746 toc10
RESET AND WATCHING TIMEOUT
PERIOD vs. SUPPLY VOLTAGE
C
SWT
= C
SRT
= 1500pF
MAX6746 toc11
27.0
V
CC
FALLING AT 1mV/µs
0.60
9.0
8.5
TIMEOUT PERIOD (ms)
V
CC
TO RESET DELAY (µs)
26.6
0.56
TIMEOUT PERIOD (ms)
RESET
8.0
WATCHDOG
7.5
7.0
6.5
6.0
26.2
0.52
25.8
0.48
25.4
0.44
25.0
-50
-25
0
25
50
75
100
125
TEMPERATURE (°C)
0.40
1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0
V
CC
(V)
1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0
V
CC
(V)
Pin Description
PIN
MAX6746
MAX6747
1
MAX6748–
MAX6751
—
MAX6752
MAX6753
—
NAME
FUNCTION
Manual Reset Input. Pull
MR
low to manually reset the device. Reset
remains asserted for the reset timeout period after
MR
is released.
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.
Logic Input. SET0 selects watchdog window ratio or disables the
watchdog timer. See Table 1.
Watchdog Timeout Input.
MAX6746–MAX6751: Connect a capacitor between SWT and ground to
set the basic watchdog timeout period (t
WD
). Determine the period by
the formula t
WD
= 5.06 x 10
6
x C
SWT
with t
WD
in seconds and C
SWT
in
Farads. Extend the basic watchdog timeout period by using the WDS
input. Connect SWT to ground to disable the watchdog timer function.
2
2
2
SWT
MAX6752/MAX6753: Connect a capacitor between SWT and ground to
set the slow watchdog timeout period (t
WD2
). Determine the slow
watchdog period by the formula: t
WD2
= 0.65 x 10
9
x C
SWT
with t
WD2
in
seconds and C
SWT
in Farads. The fast watchdog timeout period is set
by pinstrapping SET0 and SET1 (Connect SET0 high and SET1 low to
disable the watchdog timer function.) See Table 1.
3
4
3
4
3
4
SRT
GND
Reset Timeout Input. Connect a capacitor from SRT to GND to select
the reset timeout period. Determine the period as follows: t
RP
= 5.06 x
10
6
x C
SRT
with t
RP
in seconds and C
SRT
in Farads.
Ground
MR
—
1
—
RESET IN
—
—
1
SET0
_______________________________________________________________________________________
5
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