________________General Description
The MAX823/MAX824/MAX825* microprocessor (µP)
supervisory circuits combine reset output, watchdog,
and manual reset input functions in 5-pin SOT23 and
SC70 packages. They significantly improve system relia-
bility and accuracy compared to separate ICs or discrete
components. The MAX823/MAX824/MAX825 are specifi-
cally designed to ignore fast transients on VCC.
Seven preprogrammed reset threshold voltages are
available (see Reset Threshold Table). All three devices
have an active-low reset output, which is guaranteed to
be in the correct state for VCC down to 1V. The MAX823
also offers a watchdog input and manual reset input.
The MAX824 offers a watchdog input and a comple-
mentary active-high reset. The MAX825 offers a manual
reset input and a complementary active-high reset. The
Selector Guide explains the functions offered in this
series of parts.
________________________Applications
Computers and Controllers
Embedded Controllers
Intelligent Instruments
Automotive Systems
Critical µP Monitoring
Portable/Battery-Powered Equipment
Features
♦Precision Monitoring of +2.5V, +3V, +3.3V, and
+5V Power Supplies
♦Operating Current: 6µA (MAX823L/M) (SC70)
2µA (MAX825T/S/R/Z/Y) (SC70)
♦Fully Specified Over Temperature
♦140ms min Power-On Reset
♦Guaranteed RESET Valid to VCC = 1V
♦Power-Supply Transient Immunity
♦Watchdog Timer with 1.6s Timeout
(MAX823/MAX824)
♦Manual Reset Input (MAX823/MAX825)
♦No External Components
MAX823/MAX824/MAX825
5-Pin Microprocessor Supervisory Circuits With
Watchdog Timer and Manual Reset
________________________________________________________________ Maxim Integrated Products 1
15
2
34
15
2
34
15
2
34
GND
WDI
VCC
MAX823
SOT23/SC70
TOP VIEW
MR
RESET
GND
WDI
RESET
VCC
MAX824
SOT23/SC70
RESET
GND
MR
RESET
VCC
MAX825
SOT23/SC70
RESET
______________________Selector Guide
19-0487; Rev 5; 12/05
†Insert the desired suffix letter (from the Reset Threshold table) into
the blank to complete the part number. All devices are available in
tape-and-reel only. There is a 2500 piece minimum order increment.
Devices are available in both leaded and lead-free packaging.
Specify lead-free by replacing “-T” with “+T” when ordering.
MAX823
Active-Low Reset ✔
Active-High Reset —
FUNCTION
Watchdog Input ✔
MAX824
✔
✔
✔
MAX825
✔
✔
—
Manual Reset Input ✔—✔
SUFFIX RESET
THRESHOLD (V)
L4.63
M4.38
T3.08
S2.93
R2.63
Typical Operating Circuit appears at end of data sheet.
Marking Information appears at end of data sheet.
Ordering Information
PART†
TEMP. RANGE PIN-PACKAGE
MAX823_EXK-T -40°C to +85°C 5 SC70-5
MAX823_EUK-T -40°C to +125°C 5 SOT23-5
MAX824_EXK-T -40°C to +85°C 5 SC70-5
Ordering Information continued at end of data sheet.
Reset Threshold Table
Z (SC70 only) 2.32
Y (SC70 only) 2.19
Pin Configurations
*Pg
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.
MAX823/MAX824/MAX825
5-Pin Microprocessor Supervisory Circuits With
Watchdog Timer and Manual Reset
2_______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(VCC = +4.75V to +5.5V for MAX82_L, VCC = +4.5V to +5.5V for MAX82_M, VCC = +3.15V to +3.6V for MAX82_T, VCC = +3V
to +3.6V for MAX82_S, VCC = +2.7V to +3.6V for MAX82_R, VCC = +2.38V to +2.75V for MAX82_Z, VCC = +2.25V to +2.75V for
MAX82_Y, TA= TMIN to TMAX, TA= -40°C to +85°C (SC70), TA= -40°C to +125°C (SOT23), unless otherwise noted. 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 ........................................................................-0.3V to +6.0V
All Other Pins..............................................-0.3V to (VCC + 0.3V)
Input Current, All Pins Except RESET and RESET..............20mA
Output Current, RESET, RESET ..........................................20mA
Continuous Power Dissipation (TA= +70°C)
5-Pin SC70 (derate 3.1mW/°C above +70°C)...............247mW
5-Pin SOT23 (derate 7.1mW/°C above +70°C).............571mW
Operating Temperature Range
MAX82_EXK......................................................-40°C to +85°C
MAX82_EUK ...................................................-40°C to +125°C
Storage Temperature Range .............................-65°C to +150°C
Lead Temperature (soldering, 10s) .................................+300°C
MAX825T/S/R/Z/Y
PARAMETER SYMBOL MIN TYP MAX UNITS
4.56 4.63 4.70
Supply Current
(SOT23 Only) ISUPPLY
38
µA
4.5 12
10 24
4.50 4.75
Operating Voltage Range
MAX825L/M
MAX823L/M
MAX824L/M
1.0 5.5
VCC 1.2 V
512
MAX823T/S/R/Z/Y
MAX824T/S/R/Z/Y
2.59 2.63 2.66
2.55 2.70TA= TMIN to TMAX
TA= +25°C
MAX82_R
3.04 3.08 3.11
3.00 3.15TA= TMIN to TMAX
TA= +25°C
MAX82_T
2.89 2.93 2.96
2.85 3.00TA= TMIN to TMAX
TA= +25°C
CONDITIONS
MAX82_S
MR unconnected
TA= TMIN to TMAX
TA= +25°C
MAX82_L
4.31 4.38 4.45
TA= 0°C to +70°C
TA= TMIN to TMAX
4.25 4.50
WDI and MR
unconnected
TA= TMIN to TMAX
TA= +25°C
MAX82_M
MAX825T/S/R/Z/Y
Supply Current
(SC70 Only) ISUPPLY
26
µA
38
617
MAX825L/M
MAX823L/M
MAX824L/M
412
MAX823T/S/R/Z/Y
MAX824T/S/R/Z/Y
MR unconnected
WDI and MR
unconnected
2.28 2.32 2.35
2.25 2.38
Reset Threshold V
TA= TMIN to TMAX
TA= +25°C
MAX82_Z
(SC70 only)
2.16 2.19 2.22
2.13 2.25TA= TMIN to TMAX
TA= +25°C
MAX82_Y
(SC70 only)
VRST
MAX823/MAX824/MAX825
5-Pin Microprocessor Supervisory Circuits With
Watchdog Timer and Manual Reset
_______________________________________________________________________________________ 3
PARAMETER
SYMBOL
CONDITIONS
MIN TYP MAX
UNITS
MAX82_L/M 10
Reset Threshold Hysteresis MAX82_T/S/R/Z/Y 5 mV
Reset Threshold Temperature
Coefficient 40
ppm/°C
Reset Timeout Period tRP
140 200 280
ms
VCC to RESET Delay VRST - VCC = 100mV 20 µs
MAX82_L/M, VCC = VRST max,
ISOURCE = 120µAVCC - 1.5
VOH MAX82_T/S/R/Z/Y, VCC = VRST max,
ISOURCE = 30µA
0.8 ✕ VCC
MAX82_L/M, VCC = VRST min,
ISINK = 3.2mA 0.4
MAX82_T/S/R/Z/Y VCC = VRST min,
ISINK = 1.2mA 0.3
TA = 0°C to +70°C, VCC = 1V,
VCC falling, ISINK = 50µA0.3
RESET Output Voltage
VOL
TA = TMIN to TMAX, VCC = 1.2V,
VCC falling, VBATT = 0V, ISINK = 100µA
V
MAX82_L/M, RESET = 0V, VCC = 5.5V
800
RESET Output Short-Circuit
Current (Note 2)
ISOURCE
MAX82_T/S/R/Z/Y, RESET = 0V, VCC = 3.6V
400
µA
VOH VCC > 1.8V, ISOURCE = 150µA
0.8 ✕ VCC
MAX824L/M, MAX825L/M,
VCC = VRST max, ISINK = 3.2mA 0.4
RESET Output Voltage VOL MAX824T/S/R/Z/Y, MAX825T/S/R/Z/Y,
VCC = VRST max, ISINK = 1.2mA 0.3
V
WATCHDOG INPUT (MAX823/MAX824)
Watchdog Timeout Period tWD
1.12 1.60 2.40
s
WDI Pulse Width tWDI VIL = 0.4V, VIH = 0.8 ✕ VCC 50 ns
VIL
0.3 ✕ VCC
WDI Input Voltage (Note 3) VIH 0.7 ✕ VCC
V
WDI = VCC, time average
120 160
WDI Input Current (Note 4) WDI = 0, time average -20
-15
µA
ELECTRICAL CHARACTERISTICS (continued)
(VCC = +4.75V to +5.5V for MAX82_L, VCC = +4.5V to +5.5V for MAX82_M, VCC = +3.15V to +3.6V for MAX82_T, VCC = +3V
to +3.6V for MAX82_S, VCC = +2.7V to +3.6V for MAX82_R, VCC = +2.38V to +2.75V for MAX82_Z, VCC = +2.25V to +2.75V for
MAX82_Y, TA= TMIN to TMAX, TA= -40°C to +85°C (SC70), TA= -40°C to +125°C (SOT23), unless otherwise noted. Typical values
are at TA= +25°C.) (Note 1)
MAX823/MAX824/MAX825
5-Pin Microprocessor Supervisory Circuits With
Watchdog Timer and Manual Reset
4_______________________________________________________________________________________
Note 1: Over-temperature limits are guaranteed by design and not production tested.
Note 2: The RESET short-circuit current is the maximum pullup current when RESET is driven low by a µP bidirectional reset pin.
Note 3: WDI is internally serviced within the watchdog period if WDI is left unconnected.
Note 4: The WDI input current is specified as the average input current when the WDI input is driven high or low. The WDI input is
designed to drive a three-stated output device with a 10µA maximum leakage current and a maximum capacitive load of
200pF. This output device must be able to source and sink at least 200µA when active.
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
MANUAL RESET INPUT (MAX823/MAX825)
VIL
0.3 ✕ VCC
MR Input Voltage VIH 0.7 ✕ VCC
V
MR Pulse Width 1.0 µs
MR Noise Immunity (pulse width
with no reset)
100
ns
MR to Reset Delay
500
ns
MR Pullup Resistance
(internal) 35 52 75 kΩ
ELECTRICAL CHARACTERISTICS (continued)
(VCC = +4.75V to +5.5V for MAX82_L, VCC = +4.5V to +5.5V for MAX82_M, VCC = +3.15V to +3.6V for MAX82_T, VCC = +3V
to +3.6V for MAX82_S, VCC = +2.7V to +3.6V for MAX82_R, VCC = +2.38V to +2.75V for MAX82_Z, VCC = +2.25V to +2.75V for
MAX82_Y, TA= TMIN to TMAX, TA= -40°C to +85°C (SC70), TA= -40°C to +125°C (SOT23), unless otherwise noted. Typical values
are at TA= +25°C.) (Note 1)
MAX823/MAX824/MAX825
5-Pin Microprocessor Supervisory Circuits With
Watchdog Timer and Manual Reset
_______________________________________________________________________________________ 5
__________________________________________Typical Operating Characteristics
MAX823_, VCC = +5V, TA= +25°C, unless otherwise noted.)
1
3
2
6
5
4
8
7
9
-40 20 40-20 0 60 80 100 120
MAX823/4/5 toc01
TEMPERATURE (°C)
SUPPLY CURRENT (µA)
VCC SUPPLY CURRENT
vs. TEMPERATURE
MAX823L
(SC70 ONLY)
MAX824Y
MAX825R
250
150
-40 -20 40 100
RESET TIMEOUT PERIOD
vs. TEMPERATURE
170
160
180
230
240
MAX823/4/5 toc02
TEMPERATURE (°C)
RESET TIMEOUT PERIOD (ms)
020 8060
210
220
190
200
30
0
-40 -20 40 100
RESET COMPARATOR PROPAGATION DELAY
vs. TEMPERATURE
5
25
MAX823/4/5 toc03
TEMPERATURE (°C)
PROPAGATION DELAY (µs)
020 8060
20
10
15
VCC FALLING
2.0
1.0
-40 -20 40 100
WATCHDOG TIMEOUT PERIOD
vs. TEMPERATURE
1.2
1.1
1.3
1.8
1.9
MAX823/4/5 toc04
TEMPERATURE (°C)
WATCHDOG TIMEOUT PERIOD (s)
020 8060
1.6
1.7
1.4
1.5
1.06
0.94
0.96
0.98
1.00
1.02
1.04
-40 -20 40 100
NORMALIZED RESET THRESHOLD
VOLTAGE vs. TEMPERATURE
MAX823/4/5 toc05
TEMPERATURE (°C)
NORMALIZED RESET THRESHOLD (V)
020 8060
0
10
5
20
15
30
25
35
45
40
50
040608020 100 120 140 180160 200
MAX823/4/5 toc06
RESET THRESHOLD OVERDRIVE (mV), VRST - VCC
TRANSIENT DURATION (µs)
(SC70 ONLY)
MAXIMUM VCC TRANSIENT DURATION
vs. RESET THRESHOLD OVERDRIVE
RESET OCCURS
ABOVE CURVE
MAX82_Y
MAX82_R
MAX82_L
MAX823/MAX824/MAX825
5-Pin Microprocessor Supervisory Circuits With
Watchdog Timer and Manual Reset
6_______________________________________________________________________________________
Pin Description
MAX823
MAX824
MAX825
VCC
VCC
WDI
(MAX823/MAX824
ONLY)
1.25V
GND
RESET
(MAX824/MAX825
ONLY)
RESET
MR
(MAX823/MAX825
ONLY)
RESET
GENERATOR
WATCHDOG
TIMER
WATCHDOG
TRANSITION
DETECTOR
FUNCTION
1 1
Active-Low Reset Output. Pulses low for 200ms when triggered, and remains
low whenever VCC is below the reset threshold or when MR is a logic low. It
remains low for 200ms after one of the following occurs: VCC rises above the
reset threshold, the watchdog triggers a reset, or MR goes low to high.
2 2 Ground
3 —
Manual Reset Input. A logic low on MR asserts reset. Reset remains asserted as
long as MR is held low and for 200ms after MR returns high. The active-low input
has an internal 52kΩpullup resistor. It can be driven from a CMOS logic line or
shorted to ground with a switch. Leave open or connect to VCC if unused.
— 3 Active-High Reset Output. Inverse of RESET.
5 5 Supply Voltage
4 4
Watchdog Input. If WDI remains either high or low for longer than the watch-
dog timeout period, the internal watchdog timer runs out and a reset is trig-
gered. The internal watchdog timer clears whenever reset is asserted, or
whenever 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.
NAME
1RESET
2GND
4MR
3RESET
5 VCC
—WDI
Figure 1. Functional Diagram
MAX824MAX823 MAX825
PIN
MAX823/MAX824/MAX825
5-Pin Microprocessor Supervisory Circuits With
Watchdog Timer and Manual Reset
_______________________________________________________________________________________ 7
_______________Detailed Description
RESET Output
A microprocessor’s (µP’s) reset input starts the µP in a
known state. The MAX823/MAX824/MAX825 µP super-
visory circuits assert a reset to prevent code-execution
errors during power-up, power-down, and brownout
conditions. RESET is guaranteed to be a logic low for
VCC down to 1V. Once VCC exceeds the reset thresh-
old, an internal timer keeps RESET low for the specified
reset timeout period (tRP); after this interval, RESET
returns high (Figure 2).
If a brownout condition occurs (VCC dips below the
reset threshold), RESET goes low. Each time RESET is
asserted it stays low for the reset timeout period. Any
time VCC goes below the reset threshold the internal
timer restarts. RESET both sources and sinks current.
RESET on the MAX824/MAX825 is the inverse of
RESET.
Manual Reset Input (MAX823/MAX825)
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 MAX823/
MAX825, a logic low on MR asserts reset. Reset remains
asserted while MR is low, and for tRP (200ms nominal)
after it returns high. MR has an internal 52kΩpullup
resistor, so it can be left open if not used. This input can
be driven 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 func-
tion; external debounce circuitry is not required. If MR is
driven 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 (MAX823/MAX824)
In the MAX823/MAX824, the watchdog circuit monitors
the µP’s activity. If the µP does not toggle the watchdog
input (WDI) within tWD (1.6s), reset asserts. The internal
1.6s timer is cleared by either a reset pulse or by tog-
gling WDI, which detects 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 3).
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 uncon-
nected, the maximum allowable leakage current is
10µA and the maximum allowable load capacitance is
200pF.
Applications Information
Watchdog Input Current
The MAX823/MAX824 WDI inputs are internally driven
through a buffer and series resistor from the watchdog
counter (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 consumption), leave WDI low for the majority of
the watchdog 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.
VCC
1V
1V
tRD
VRST VRST
tRD
RESET
GND
RESET
tRP
tRP
Figure 2. Reset Timing Diagram
VCC
tWD tRP
tRP
tRST
WDI
RESET*
*RESET ON THE MAX824/MAX825 IS THE INVERSE OF RESET.
Figure 3. MAX823/MAX824 Watchdog Timing Relationship
MAX823/MAX824/MAX825
5-Pin Microprocessor Supervisory Circuits With
Watchdog Timer and Manual Reset
8_______________________________________________________________________________________
Interfacing to µPs with
Bidirectional Reset Pins
The RESET output maximum pullup current is 800µA for
L/M versions (400µA for T/S/R/Z/Y versions). This allows
µPs with bidirectional resets, such as the 68HC11, to
force RESET low when the MAX823/MAX824/MAX825
are pulling RESET high (Figure 4).
Negative-Going VCC Transients
These supervisors are relatively immune to short-
duration, 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 MAX823_’s Maximum VCC Transient Duration vs.
Reset Threshold Overdrive, for which reset pulses are
not generated. The graph was produced using nega-
tive-going VCC pulses, starting at 5V 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.
An optional 0.1µF bypass capacitor mounted close to
VCC provides additional transient immunity.
Watchdog Software Considerations
(MAX823/MAX824)
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 5 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.
MAX823
MAX824
MAX825
µP
VCC
VCC
VCC
VCC
GND
GND
RESET
ISOURCE MAX = 800µA L, M
400µA T, S, R, Z, Y
RESET
GENERATOR
Figure 4. Interfacing to µPs with Bidirectional Resets
START
SET WDI
HIGH
PROGRAM
CODE
SUBROUTINE OR
PROGRAM LOOP
SET WDI LOW
RETURN
Figure 5. Watchdog Flow Diagram
MAX823/MAX824/MAX825
5-Pin Microprocessor Supervisory Circuits With
Watchdog Timer and Manual Reset
_______________________________________________________________________________________ 9
Typical Operating Circuit ____________________Chip Information
TRANSISTOR COUNT: 607
PROCESS TECHNOLOGY: BiCMOS
MAX823 µP
VCC
VCC
VCC
GND
GND
MANUAL
RESET
RESET
I/O
RESET
MR
WDI
Ordering Information (continued)
PART†
TEMP. RANGE
PIN-PACKAGE
MAX824_EUK-T
-40°C to +125°C
5 SOT23-5
MAX825_EXK-T -40°C to +85°C 5 SC70-5
MAX825_EUK-T
-40°C to +125°C
5 SOT23-5
†Insert the desired suffix letter (from the Reset Threshold table) into
the blank to complete the part number. All devices are available in
tape-and-reel only. There is a 2,500 piece minimum order increment.
Devices are available in both leaded and lead-free packaging.
Specify lead-free by replacing “-T” with “+T” when ordering.
MARKING INFORMATION (TOP)
AAAI = MAX823L
AAAJ = MAX823M
AAAK = MAX823T
AAAL = MAX823S
AAAM = MAX823R
AAAN = MAX824L
AAAO = MAX824M
AAAP = MAX824T
AAAQ = MAX824S
AAAR = MAX824R
AAAS = MAX825L
AAAT = MAX825M
AAAU = MAX825T
AAAV = MAX825S
AAAW = MAX825R
XXXX (SOT ONLY)
MARKING INFORMATION (TOP)
XXXX (SC70 ONLY)
AAL = MAX823L
AAM = MAX823M
AAP = MAX823R
AAO = MAX823S
AAN = MAX823T
AAR = MAX823Y
AAQ = MAX823Z
AAS = MAX824L
AAT = MAX824M
AAW = MAX824R
AAV = MAX824S
AAU = MAX824T
AAY = MAX824Y
AAX = MAX824Z
AAZ = MAX825L
ABA = MAX825M
ABD = MAX825R
ABC = MAX825S
ABB = MAX825T
ABF = MAX825Y
ABE = MAX825Z
Marking Information
MAX823/MAX824/MAX825
5-Pin Microprocessor Supervisory Circuits With
Watchdog Timer and Manual Reset
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.
10 __________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 (408) 737-7600
©2005 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products, Inc.
SOT-23 5L .EPS
E
1
1
21-0057
PACKAGE OUTLINE, SOT-23, 5L
Package Information
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information,
go to www.maxim-ic.com/packages.)