MAX6821/MAX6825
Low-Voltage SOT23 µP Supervisors
with Manual Reset and Watchdog Timer
Features
General Description
The MAX6821–MAX6825 are low-voltage microproces-
sor (µP) supervisory circuits that combine voltage mon-
itoring, watchdog timer, and manual reset input func-
tions in a 5-pin SOT23 package. Microprocessor super-
visory circuits significantly improve system reliability and
accuracy compared to separate ICs or discrete compo-
nents. These devices assert a reset signal whenever the
monitored voltage drops below its preset threshold, keep-
ing it asserted for a minimum timeout period after V
CC
rises
above the threshold. In addition, a watchdog timer monitors
against code execution errors. A debounced manual reset
is also available. The MAX6821–MAX6825 monitor voltag-
es from +1.8V to +5.0V. These outputs are guaranteed 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.
●
Monitors +1.8V, +2.5V, +3.0V, +3.3V, +5.0V Supplies
●
140ms (min) Reset Timeout Delay
●
1.6s Watchdog Timeout Period (MAX6821/MAX6822/
MAX6823/MAX6824)
●
Manual Reset Input (MAX6821/MAX6822/MAX6823/
MAX6825)
●
Three Reset Output Options
Push-Pull
RESET
Push-Pull RESET
Open-Drain
RESET
●
Guaranteed Reset Valid to V
CC
= +1.0V
●
Immune to Short Negative V
CC
Transients
●
No External Components
●
Small 5-Pin SOT23 Packages
Ordering Information
PART*
MAX6821_UK-T
MAX6822_UK-T
MAX6823_UK-T
MAX6824_UK-T
TEMP RANGE
-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
Applications
●
Set-Top Boxes
●
Computers and Con-
trollers
●
Embedded Controllers
●
Intelligent Instruments
●
Critical µP Monitoring
●
Portable/Battery-
Powered Equipment
MAX6825_UK-T
-40°C to +125°C
5 SOT23-5
*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(Pb)-free packag-
ing.Specify lead-free by replacing “-T” with “+T” when ordering.
Threshold Suffix Guide
RESET
THRESHOLD (V)
L
4.63
M
4.38
T
3.08
S
2.93
R
2.63
Z
2.32
Y
2.19
W
1.67
V
1.58
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.
SUFFIX
Pin Configurations
TOP VIEW
RESET(RESET)
1
5
V
CC
GND 2
MAX6821
MAX6822
MAX6823
4
WDI
MR
3
(RESET) MAX6821 ONLY
SOT23-5
Pin Configurations continued at end of data sheet.
Typical Operating Circuit appears at end of data sheet.
19-1868; Rev 3; 7/14
MAX6821/MAX6825
Low-Voltage SOT23 µP Supervisors
with Manual Reset and Watchdog Timer
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
PARAMETER
Operating Voltage Range
(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)
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
MIN
1.0
1.2
TYP
MAX
5.5
5.5
UNITS
V
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
TA = -40°C to +85°C
4.50
10
7
5
4.63
20
30
16
25
12
20
4.75
µA
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
4.47
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
4.38
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
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
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)
2 × V
TH
20
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MAX6821/MAX6825
Low-Voltage SOT23 µP Supervisors
with Manual Reset and Watchdog Timer
Electrical Characteristics (continued)
PARAMETER
Reset Timeout Period
(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)
SYMBOL
tRP
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
MIN
140
TYP
200
MAX
280
UNITS
ms
100
320
0.3
RESET
Output LOW
(Push-Pull or Open-Drain)
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
0.8 × V
CC
0.8 × V
CC
0.8 × V
CC
0.3
0.3
0.4
V
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
V
Open-Drain
RESET
Output
Leakage Current (Note 1)
I
LKG
V
CC
> VTH, RESET not asserted
V
CC
≥
1.0V, I
SOURCE
= 1µA, reset asserted,
T
A
= 0
°
C to +85
°
C
0.8 × V
CC
1.0
µA
RESET Output HIGH
(Push-Pull Only)
V
OH
V
CC
≥
1.50V, I
SOURCE
= 100µA, reset asserted 0.8 × V
CC
V
CC
≥
2.55V, I
SOURCE
= 500µA, reset asserted 0.8 × V
CC
V
CC
≥
4.25V, I
SOURCE
= 800µA, reset asserted 0.8 × V
CC
V
CC
≥
1.8V, I
SINK
= 500µA, reset not asserted
0.3
0.3
0.4
0.3 × V
CC
V
RESET Output LOW
(Push-Pull Only)
VOL
V
CC
≥
3.15V, I
SINK
= 1.2mA, reset not asserted
V
CC
≥
4.75V, I
SINK
= 3.2mA, reset not asserted
V
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
IH
I
WDI
V
IL
T
A
= -40°C to +85°C
1.12
0.80
50
0.7 × V
CC
0.3 × V
CC
120
160
1.60
2.40
2.60
T
A
= -40°C to +125°C
s
ns
V
µA
25
V
IH
V
IL
0.7 × V
CC
1
100
200
50
75
V
µs
ns
ns
kΩ
WDI = 0, time average
-20
-15
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.
WDI = V
CC
, time average
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MAX6821/MAX6825
Low-Voltage SOT23 µP Supervisors
with Manual Reset and Watchdog Timer
Typical Operating Characteristics
(T
A
= +25°C, unless otherwise noted.)
MAX6821 toc02
MAX6821 toc01
12
SUPPLY CURRENT (µA)
11
10
9
8
7
6
5
4
3
RESET TIMEOUT PERIOD (ms)
PROPAGATION DELAY (µs)
V
CC
= +5V, L VERSION
240
230
220
210
200
190
180
170
160
150
V
CC
FALLING, V
CC
= V
TH
- 100mV
30
25
20
15
10
5
V
CC
= +3.3V, S VERSION
V
CC
= +1.8V, V VERSION
-40 -20
0
20
40
60
80 100 120
-40 -20
0
20
40
60
80 100 120
0
-40 -20
0
20
40
60
80 100 120
TEMPERATURE (°C)
TEMPERATURE (°C)
TEMPERATURE (°C)
WATCHDOG TIMEOUT PERIOD (s)
1.9
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
MAX6821 toc04
1.02
1.00
0.98
0.96
0.94
-40 -20
TRANSIENT DURATION (µs)
1.04
RESET THRESHOLD (V)
MAX6821 toc05
100
80
60
40
20
0
RESET OCCURS
ABOVE CURVE
0
20
40
60
80 100 120
0
20 40 60 80 100 120 140 160 180 200
TEMPERATURE (°C)
TEMPERATURE (°C)
RESET THRESHOLD OVERDRIVE (mV), V
TH
- V
CC
MAX6821 toc07
V
CC
= +2.9V
0.30
0.25
2.90
2.88
2.86
V
OUT
(V)
2.84
2.82
2.80
2.78
2.76
V
CC
= +2.9V
V
OUT
(V)
0.20
0.15
0.10
0.05
0
0
1
2
3
4
5
6
7
2.74
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)
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MAX6821 toc08
0.35
VOLTAGE OUTPUT LOW
vs. SINK CURRENT
2.92
VOLTAGE OUTPUT HIGH
vs. SOURCE CURRENT
MAX6821 toc06
2.0
WATCHDOG TIMEOUT PERIOD
vs. TEMPERATURE
1.06
NORMALIZED RESET THRESHOLD
DELAY vs. TEMPERATURE
MAXIMUM V
CC
TRANSIENT DURATION
vs. RESET THRESHOLD OVERDRIVE
120
MAX6821 toc03
13
SUPPLY CURRENT
vs. TEMPERATURE
250
RESET TIMEOUT PERIOD
vs. TEMPERATURE
35
V
CC
TO RESET OUTPUT DELAY
vs. TEMPERATURE
MAX6821/MAX6825
Low-Voltage SOT23 µP Supervisors
with Manual Reset and Watchdog Timer
Pin Description
PIN
NAME
MAX6821 MAX6822 MAX6823 MAX6824 MAX6825
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
1
1
1
1
RESET
1
3
3
RESET
2
3
2
3
2
3
2
2
4
GND
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 out-
put 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
Manual Reset Input
Many µP-based products require manual reset capabili-
ty, 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
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).
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