19-1868; Rev 2; 12/05
Low-Voltage SOT23 µP Supervisors with
Manual Reset and Watchdog Timer
General Description
The MAX6821–MAX6825 are low-voltage microprocessor
(µP) supervisory circuits that combine voltage monitor-
ing, watchdog timer, and manual reset input functions in
a 5-pin SOT23 package. Microprocessor supervisory cir-
cuits significantly improve system reliability and accura-
cy compared to separate ICs or discrete components.
These devices assert a reset signal whenever the moni-
tored voltage drops below its preset threshold, keeping it
asserted for a minimum timeout period after V
CC
rises
above the threshold. In addition, a watchdog timer moni-
tors against code execution errors. A debounced manual
reset is also available. The MAX6821–MAX6825 monitor
voltages from +1.8V to +5.0V. These outputs are guaran-
teed to be in the correct state for V
CC
down to +1.0V.
Nine preprogrammed reset threshold voltages are
available (see the
Threshold Suffix Guide).
The
MAX6821, MAX6822, and MAX6823 all have a manual
reset input and a watchdog timer. The MAX6821 has
push-pull RESET, the MAX6822 has open-drain
RESET,
and the MAX6823 has push-pull
RESET.
The MAX6824
has a watchdog timer and both push-pull
RESET
and
push-pull RESET. The MAX6825 has a manual reset
input and both push-pull
RESET
and push-pull RESET.
The
Selector Guide
explains the functions offered in
this series of parts.
Features
o
Monitors +1.8V, +2.5V, +3.0V, +3.3V, +5.0V
Supplies
o
140ms (min) Reset Timeout Delay
o
1.6s Watchdog Timeout Period
(MAX6821/MAX6822/MAX6823/MAX6824)
o
Manual Reset Input
(MAX6821/MAX6822/MAX6823/MAX6825)
o
Three Reset Output Options
Push-Pull
RESET
Push-Pull RESET
Open-Drain
RESET
o
Guaranteed Reset Valid to V
CC
= +1.0V
o
Immune to Short Negative V
CC
Transients
o
No External Components
o
Small 5-Pin SOT23 Packages
MAX6821–MAX6825
Ordering Information
PART*
MAX6821_UK-T
MAX6822_UK-T
MAX6823_UK-T
MAX6824_UK-T
MAX6825_UK-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
PIN-PACKAGE
5 SOT23-5
5 SOT23-5
5 SOT23-5
5 SOT23-5
5 SOT23-5
________________________Applications
Set-Top Boxes
Computers and
Controllers
Embedded Controllers
Intelligent Instruments
Automotive Systems
Critical µP Monitoring
Portable/Battery-
Powered Equipment
*Insert
the desired suffix letter (from the table below) into the blank
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.
Threshold Suffix Guide
Pin Configurations
SUFFIX
L
RESET
THRESHOLD (V)
4.63
4.38
3.08
2.93
2.63
2.32
2.19
1.67
1.58
TOP VIEW
RESET(RESET)
1
5
V
CC
M
T
S
R
Z
Y
4
WDI
GND
2
MAX6821
MAX6822
MAX6823
MR
3
W
V
(RESET) MAX6821 ONLY
SOT23-5
Pin Configurations continued at end of data sheet.
Typical Operating Circuit appears at end of data sheet.
Note:
Bold indicates standard versions. Samples are typically
available for standard versions only. All parts require a 2.5k
minimum order increment. Contact factory for availability.
Selector Guide appears at end of data sheet.
1
________________________________________________________________
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.
Low-Voltage SOT23 µP Supervisors with
Manual Reset and Watchdog Timer
MAX6821–MAX6825
ABSOLUTE MAXIMUM RATINGS
V
CC
to GND ...........................................................-0.3V to +6.0V
Open-Drain
RESET................................................-0.3V
to +6.0V
Push-Pull
RESET,
RESET,
MR,
WDI ...........-0.3V to (V
CC
+ 0.3V)
Input Current (V
CC
) .............................................................20mA
Output Current (RESET, RESET).........................................20mA
Continuous Power Dissipation (T
A
= +70°C)
5-Pin SOT23 (derate 7.1mW/°C above +70°C)............571mW
Operating Temperature Range .........................-40°C to +125°C
Junction Temperature ......................................................+150°C
Storage Temperature Range .............................-65°C to +150°C
Lead Temperature (soldering, 10s) .................................+300°C
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
ELECTRICAL CHARACTERISTICS
(V
CC
= +4.5V to +5.5V for MAX682_L/M, V
CC
= +2.7V to +3.6V for MAX682_T/S/R, V
CC
= +2.1V to +2.75V for MAX682_Z/Y, V
CC
=
+1.53V to +2.0V for MAX682_W/V, T
A
= -40°C to +125°C, unless otherwise specified. Typical values are at T
A
= +25°C.) (Note 1)
PARAMETER
Operating Voltage Range
SYMBOL
V
CC
CONDITIONS
T
A
= 0°C to +85°C
T
A
= -40°C to +125°C
V
CC
= +5.5V, no load
V
CC
Supply Current
(MR
and WDI Unconnected)
I
CC
V
CC
= +3.6V, no load
V
CC
= +3.6V, no load
(MAX6825 only)
MAX682_L
MAX682_M
MAX682_T
MAX682_S
V
CC
Reset Threshold
(V
CC
Falling)
V
TH
MAX682_R
MAX682_Z
MAX682_Y
MAX682_W
MAX682_V
Reset Threshold Temperature
Coefficient
Reset Threshold Hysteresis
V
CC
to Reset Output Delay
t
RD
V
CC
= V
TH
to (V
TH
- 100mV)
T
A
= -40°C to +85°C
T
A
= -40°C to +125°C
T
A
= -40°C to +85°C
T
A
= -40°C to +125°C
T
A
= -40°C to +85°C
T
A
= -40°C to +125°C
T
A
= -40°C to +85°C
T
A
= -40°C to +125°C
T
A
= -40°C to +85°C
T
A
= -40°C to +125°C
T
A
= -40°C to +85°C
T
A
= -40°C to +125°C
T
A
= -40°C to +85°C
T
A
= -40°C to +125°C
T
A
= -40°C to +85°C
T
A
= -40°C to +125°C
T
A
= -40°C to +85°C
T
A
= -40°C to +125°C
T
A
= -40°C to +85°C
T
A
= -40°C to +125°C
T
A
= -40°C to +85°C
T
A
= -40°C to +125°C
T
A
= -40°C to +85°C
4.50
4.47
4.25
4.22
3.00
2.97
2.85
2.83
2.55
2.53
2.25
2.24
2.12
2.11
1.62
1.61
1.52
4.63
4.63
4.38
4.38
3.08
3.08
2.93
2.93
2.63
2.63
2.32
2.32
2.19
2.19
1.67
1.67
1.58
60
2
✕
V
TH
20
5
7
MIN
1.0
1.2
10
TYP
MAX
5.5
5.5
20
30
16
25
12
20
4.75
4.78
4.50
4.53
3.15
3.17
3.00
3.02
2.70
2.72
2.38
2.40
2.25
2.27
1.71
1.72
1.62
ppm/°C
mV
µs
V
µA
UNITS
V
2
_______________________________________________________________________________________
Low-Voltage SOT23 µP Supervisors with
Manual Reset and Watchdog Timer
ELECTRICAL CHARACTERISTICS (continued)
(V
CC
= +4.5V to +5.5V for MAX682_L/M, V
CC
= +2.7V to +3.6V for MAX682_T/S/R, V
CC
= +2.1V to +2.75V for MAX682_Z/Y, V
CC
=
+1.53V to +2.0V for MAX682_W/V, T
A
= -40°C to +125°C, unless otherwise specified. Typical values are at T
A
= +25°C.) (Note 1)
PARAMETER
Reset Timeout Period
SYMBOL
t
RP
CONDITIONS
T
A
= -40°C to +85°C
T
A
= -40°C to +125°C
V
CC
≥
1.0V, I
SINK
= 50µA, reset asserted,
T
A
= 0°C to +85°C
V
OL
V
CC
≥
1.2V, I
SINK
= 100µA, reset asserted
V
CC
≥
2.55V, I
SINK
= 1.2mA, reset asserted
V
CC
≥
4.25V, I
SINK
= 3.2mA, reset asserted
V
CC
≥
1.8V, I
SOURCE
= 200µA, reset not
asserted
RESET
Output HIGH
(Push-Pull Only)
V
OH
V
CC
≥
3.15V, I
SOURCE
= 500µA, reset not
asserted
V
CC
≥
4.75V, I
SOURCE
= 800µA, reset not
asserted
Open-Drain
RESET
Output
Leakage Current (Note 1)
I
LKG
V
CC
> V
TH
,
RESET
not asserted
V
CC
≥
1.0V, I
SOURCE
= 1µA, reset asserted,
T
A
= 0°C to +85°C
RESET Output HIGH
(Push-Pull Only)
V
OH
V
CC
≥
1.50V, I
SOURCE
= 100µA, reset asserted
V
CC
≥
2.55V, I
SOURCE
= 500µA, reset asserted
V
CC
≥
4.25V, I
SOURCE
= 800µA, reset asserted
RESET Output LOW
(Push-Pull Only)
V
CC
≥
1.8V, I
SINK
= 500µA, reset not asserted
VOL
V
CC
≥
3.15V, I
SINK
= 1.2mA, reset not asserted
V
CC
≥
4.75V, I
SINK
= 3.2mA, reset not asserted
V
IL
V
IH
0.7
✕
V
CC
1
100
200
25
T
A
= -40°C to +85°C
T
A
= -40°C to +125°C
1.12
0.80
50
0.3
✕
V
CC
0.7
✕
V
CC
WDI = V
CC
, time average
WDI = 0, time average
-20
120
-15
160
50
1.60
75
2.40
2.60
0.8
✕
V
CC
0.8
✕
VCC
0.8
✕
VCC
0.8
✕
VCC
0.3
0.3
0.4
0.3
✕
V
CC
V
V
0.8
✕
V
CC
0.8
✕
V
CC
0.8
✕
V
CC
1.0
µA
V
MIN
140
100
TYP
200
MAX
280
320
0.3
0.3
0.3
0.4
V
UNITS
ms
MAX6821–MAX6825
RESET
Output LOW
(Push-Pull or Open-Drain)
MANUAL RESET INPUT (MAX6821/MAX6822/MAX6823/MAX6825)
MR
Input Voltage
MR
Minimum Input Pulse
MR
Glitch Rejection
MR
to Reset Delay
MR
Pullup Resistance
WATCHDOG INPUT (MAX6821/MAX6822/MAX6823/MAX6824)
Watchdog Timeout Period
WDI Pulse Width (Note 2)
WDI Input Voltage
WDI Input Current
t
WD
t
WDI
V
IL
V
IH
I
WDI
s
ns
V
µA
V
µs
ns
ns
kΩ
Note 1:
Over-temperature limits are guaranteed by design and not production tested. Devices tested at T
A
= +25°C.
Note 2:
Guaranteed by design and not production tested.
_______________________________________________________________________________________
3
Low-Voltage SOT23 µP Supervisors with
Manual Reset and Watchdog Timer
MAX6821–MAX6825
Typical Operating Characteristics
(T
A
= +25°C, unless otherwise noted.)
SUPPLY CURRENT
vs. TEMPERATURE
MAX6821 toc01
RESET TIMEOUT PERIOD
vs. TEMPERATURE
MAX6821 toc02
V
CC
TO RESET OUTPUT DELAY
vs. TEMPERATURE
V
CC
FALLING, V
CC
= V
TH
- 100mV
MAX6821 toc03
13
12
11
SUPPLY CURRENT (µA)
10
9
8
7
6
5
4
3
-40 -20
0
20
40
60
80
100 120
TEMPERATURE (°C)
V
CC
= +3.3V, S VERSION
V
CC
= +1.8V, V VERSION
V
CC
= +5V, L VERSION
250
240
RESET TIMEOUT PERIOD (ms)
230
220
210
200
190
180
170
160
150
-40 -20
0
20
40
60
80
100 120
TEMPERATURE (°C)
35
30
PROPAGATION DELAY (µs)
25
20
15
10
5
0
-40 -20
0
20
40
60
80
100 120
TEMPERATURE (°C)
WATCHDOG TIMEOUT PERIOD
vs. TEMPERATURE
MAX6821 toc04
NORMALIZED RESET THRESHOLD
DELAY vs. TEMPERATURE
MAX6821 toc05
MAXIMUM V
CC
TRANSIENT DURATION
vs. RESET THRESHOLD OVERDRIVE
MAX6821 toc06
2.0
1.9
WATCHDOG TIMEOUT PERIOD (s)
1.8
1.7
1.6
1.5
1.4
1.3
1.2
1.1
1.0
-40 -20
0
20
40
60
80
100 120
TEMPERATURE (°C)
1.06
1.04
RESET THRESHOLD (V)
1.02
1.00
0.98
0.96
0.94
-40 -20
120
100
80
60
40
20
0
TRANSIENT DURATION (µs)
RESET OCCURS
ABOVE CURVE
0
20
40
60
80
100 120
0
20 40 60 80 100 120 140 160 180 200
RESET THRESHOLD OVERDRIVE (mV), V
TH
- V
CC
TEMPERATURE (°C)
VOLTAGE OUTPUT LOW
vs. SINK CURRENT
MAX6821 toc07
VOLTAGE OUTPUT HIGH
vs. SOURCE CURRENT
V
CC
= +2.9V
2.90
2.88
2.86
V
OUT
(V)
2.84
2.82
2.80
2.78
MAX6821 toc08
0.35
0.30
0.25
V
OUT
(V)
0.20
0.15
0.10
0.05
0
0
V
CC
= +2.9V
2.92
2.76
2.74
1
2
3
4
5
6
7
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
I
SOURCE
(mA)
I
SINK
(mA)
4
_______________________________________________________________________________________
Low-Voltage SOT23 µP Supervisors with
Manual Reset and Watchdog Timer
Pin Description
PIN
MAX6821 MAX6822 MAX6823 MAX6824 MAX6825 NAME
PIN NUMBERS
FUNCTION
Active-Low Open-Drain or Push-Pull Reset Output.
RESET
changes from high to low when the V
CC
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 V
CC
exceeds the device reset threshold,
MR
goes low to
high, or the watchdog triggers a reset.
Active-High Push-Pull Reset Output. RESET changes from low to
high when the V
CC
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 V
CC
exceeds the device
reset threshold,
MR
goes low to high, or the watchdog triggers a
reset.
Ground
Active-Low Manual Reset Input. Internal 50kΩ pullup to V
CC
. 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 V
CC
if unused.
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.
Supply Voltage and Input for Reset Threshold Monitor
MAX6821–MAX6825
1
1
1
1
RESET
1
3
3
RESET
2
2
2
2
2
GND
3
3
3
4
MR
4
4
4
4
WDI
5
5
5
5
5
V
CC
Detailed Description
RESET
/RESET Output
A µP’s reset input starts the µP in a known state. The
MAX6821–MAX6825 µP supervisory circuits assert a
reset to prevent code-execution errors during power-
up, power-down, and brownout conditions. Whenever
V
CC
falls below the reset threshold, the reset output
asserts low for
RESET
and high for RESET. Once V
CC
exceeds the reset threshold, an internal timer keeps the
reset output asserted for the specified reset timeout
period (t
RP
); after this interval, reset output returns to its
original state (see Figure 2).
returns high.
MR
has an internal 50kΩ pullup 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
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
In the MAX6821–MAX6824, the watchdog circuit moni-
tors 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 timoeout 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 (see Figure 3).
5
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. On the MAX6821/
MAX6822/MAX6823/MAX6825, a logic low on
MR
asserts a reset. Reset remains asserted while
MR
is
low, and for the timeout period (140ms min) after it
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