MAXIM MAX824TEXK-T

19-0487; Rev 4; 7/01
5-Pin Microprocessor Supervisory Circuits With
Watchdog Timer and Manual Reset
Features
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 reliability and accuracy compared to separate ICs or discrete
components. The MAX823/MAX824/MAX825 are specifically 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 complementary 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.
♦ 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
Ordering Information
PART†
*Patents Pending
________________________Applications
Computers and Controllers
Embedded Controllers
Intelligent Instruments
Automotive Systems
Critical µP Monitoring
Portable/Battery-Powered Equipment
RESET
THRESHOLD (V)
L
4.63
M
4.38
T
3.08
2.93
2.63
Z (SC70 only)
2.32
Y (SC70 only)
2.19
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.
SUFFIX
S
PIN-PACKAGE
-40°C to +85°C
†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.
Reset Threshold Table
R
TEMP. RANGE
MAX823_EXK-T
______________________Selector Guide
FUNCTION
MAX823
MAX824
MAX825
Active-Low Reset
✔
✔
✔
Active-High Reset
✔
✔
Watchdog Input
—
✔
✔
Manual Reset Input
✔
—
—
✔
Typical Operating Circuit appears at end of data sheet.
Marking Information appears at end of data sheet.
Pin Configurations
TOP VIEW
RESET 1
GND 2
5
VCC
MAX823
MR 3
GND 2
4
SOT23/SC70
RESET 1
WDI
5 VCC
MAX824
RESET 3
GND 2
4 WDI
SOT23/SC70
RESET 1
5 VCC
MAX825
RESET 3
4
MR
SOT23/SC70
________________________________________________________________ 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.
1
MAX823/MAX824/MAX825
________________General Description
MAX823/MAX824/MAX825
5-Pin Microprocessor Supervisory Circuits With
Watchdog Timer and Manual Reset
ABSOLUTE MAXIMUM RATINGS
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
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
(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)
PARAMETER
Operating Voltage Range
Supply Current
(SOT23 Only)
SYMBOL
VCC
ISUPPLY
CONDITIONS
1.0
TA = TMIN to TMAX
1.2
WDI and MR
unconnected
MR unconnected
Supply Current
(SC70 Only)
ISUPPLY
WDI and MR
unconnected
MR unconnected
VRST
5
12
MAX825L/M
4.5
12
MAX825T/S/R/Z/Y
3
8
MAX823L/M
MAX824L/M
6
17
MAX823T/S/R/Z/Y
MAX824T/S/R/Z/Y
4
12
MAX825L/M
3
8
MAX825T/S/R/Z/Y
2
6
4.63
4.70
4.38
4.45
3.08
3.11
4.50
4.31
TA = TMIN to TMAX
4.25
TA = +25°C
3.04
TA = TMIN to TMAX
3.00
TA = +25°C
2.89
TA = TMIN to TMAX
2.85
TA = +25°C
2.59
TA = TMIN to TMAX
2.55
MAX82_Z
(SC70 only)
TA = +25°C
2.28
TA = TMIN to TMAX
2.25
MAX82_Y
(SC70 only)
TA = +25°C
2.16
TA = TMIN to TMAX
2.13
MAX82_R
2
MAX823T/S/R/Z/Y
MAX824T/S/R/Z/Y
TA = +25°C
MAX82_S
5.5
24
TA = TMIN to TMAX
MAX82_T
MAX
10
4.56
MAX82_M
TYP
MAX823L/M
MAX824L/M
TA = +25°C
MAX82_L
Reset Threshold
MIN
TA = 0°C to +70°C
UNITS
V
µA
µA
4.75
4.50
3.15
2.93
2.96
3.00
2.63
2.66
2.70
2.32
2.35
2.19
2.22
2.38
_______________________________________________________________________________________
2.25
V
5-Pin Microprocessor Supervisory Circuits With
Watchdog Timer and Manual Reset
(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)
PARAMETER
SYMBOL
Reset Threshold Hysteresis
CONDITIONS
MIN
TYP
MAX82_L/M
10
MAX82_T/S/R/Z/Y
5
Reset Threshold Temperature
Coefficient
Reset Timeout Period
MAX
mV
40
tRP
VCC to RESET Delay
140
VOH
RESET Output Voltage
VOL
ppm/°C
200
VRST - VCC = 100mV
280
VCC - 1.5
MAX82_T/S/R/Z/Y, VCC = VRST max,
ISOURCE = 30µA
0.8 ✕ VCC
ms
µs
20
MAX82_L/M, VCC = VRST max,
ISOURCE = 120µA
UNITS
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 = 50µA
0.3
V
TA = TMIN to TMAX, VCC = 1.2V,
VCC falling, VBATT = 0V, ISINK = 100µA
RESET Output Short-Circuit
Current (Note 2)
ISOURCE
VOH
RESET Output Voltage
VOL
MAX82_L/M, RESET = 0V, VCC = 5.5V
800
MAX82_T/S/R/Z/Y, RESET = 0V, VCC = 3.6V
400
VCC > 1.8V, ISOURCE = 150µA
µA
0.8 ✕ VCC
MAX824L/M, MAX825L/M,
VCC = VRST max, ISINK = 3.2mA
0.4
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
WDI Pulse Width
tWDI
WDI Input Voltage (Note 3)
WDI Input Current (Note 4)
1.12
VIL = 0.4V, VIH = 0.8 ✕ VCC
1.60
2.40
50
ns
0.3 ✕ VCC
VIL
0.7 ✕ VCC
VIH
WDI = VCC, time average
WDI = 0, time average
120
-20
s
-15
160
V
µA
_______________________________________________________________________________________
3
MAX823/MAX824/MAX825
ELECTRICAL CHARACTERISTICS (continued)
MAX823/MAX824/MAX825
5-Pin Microprocessor Supervisory Circuits With
Watchdog Timer and Manual Reset
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)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
MANUAL RESET INPUT (MAX823/MAX825)
MR Input Voltage
MR Pulse Width
0.3 ✕ VCC
VIL
VIH
0.7 ✕ VCC
V
µs
1.0
MR Noise Immunity (pulse width
with no reset)
100
ns
MR to Reset Delay
500
ns
MR Pullup Resistance
(internal)
Note 1:
Note 2:
Note 3:
Note 4:
4
35
52
75
kΩ
Over-temperature limits are guaranteed by design and not production tested.
The RESET short-circuit current is the maximum pullup current when RESET is driven low by a µP bidirectional reset pin.
WDI is internally serviced within the watchdog period if WDI is left unconnected.
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.
_______________________________________________________________________________________
5-Pin Microprocessor Supervisory Circuits With
Watchdog Timer and Manual Reset
RESET TIMEOUT PERIOD
vs. TEMPERATURE
MAX823L
7
6
5
MAX824Y
4
3
MAX825R
2
220
210
200
190
180
170
VCC FALLING
25
20
15
10
5
160
150
-40 -20
0
20
40
60
80
0
-40
100 120
-20
0
20
40
60
80
100
-20
0
20
40
60
80
100
TEMPERATURE (°C)
TEMPERATURE (°C)
WATCHDOG TIMEOUT PERIOD
vs. TEMPERATURE
NORMALIZED RESET THRESHOLD
VOLTAGE vs. TEMPERATURE
MAXIMUM VCC TRANSIENT DURATION
vs. RESET THRESHOLD OVERDRIVE
1.8
1.7
1.6
1.5
1.4
1.3
1.2
1.1
1.06
1.04
1.02
1.00
0.98
0.96
-20
0
20
40
60
TEMPERATURE (°C)
80
100
(SC70 ONLY)
45
40
35
30
25
RESET OCCURS
ABOVE CURVE
20
MAX82_Y
15
10
MAX82_R
5
0.94
1.0
50
TRANSIENT DURATION (µs)
1.9
NORMALIZED RESET THRESHOLD (V)
MAX823/4/5 toc04
2.0
-40
-40
TEMPERATURE (°C)
MAX823/4/5 toc06
1
WATCHDOG TIMEOUT PERIOD (s)
230
30
MAX823/4/5 toc03
240
MAX823/4/5 toc05
SUPPLY CURRENT (µA)
8
250
MAX823/4/5 toc02
(SC70 ONLY)
RESET TIMEOUT PERIOD (ms)
MAX823/4/5 toc01
9
RESET COMPARATOR PROPAGATION DELAY
vs. TEMPERATURE
PROPAGATION DELAY (µs)
VCC SUPPLY CURRENT
vs. TEMPERATURE
MAX82_L
0
-40
-20
0
20
40
60
TEMPERATURE (°C)
80
100
0
20 40 60 80 100 120 140 160 180 200
RESET THRESHOLD OVERDRIVE (mV), VRST - VCC
_______________________________________________________________________________________
5
MAX823/MAX824/MAX825
__________________________________________Typical Operating Characteristics
MAX823_, VCC = +5V, TA = +25°C, unless otherwise noted.)
5-Pin Microprocessor Supervisory Circuits With
Watchdog Timer and Manual Reset
MAX823/MAX824/MAX825
Pin Description
MAX823
PIN
MAX824
MAX825
NAME
FUNCTION
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.
1
1
1
RESET
2
2
2
GND
3
—
4
MR
—
3
3
RESET
Ground
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 52kΩ pullup 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.
Active-High Reset Output. Inverse of RESET.
4
4
—
WDI
Watchdog Input. If WDI remains either high or low for longer than the watchdog timeout period, the internal watchdog timer runs out and a reset is triggered. 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.
5
5
5
VCC
Supply Voltage
VCC
MAX823
MAX824
MAX825
RESET
GENERATOR
VCC
RESET
RESET
(MAX824/MAX825
ONLY)
1.25V
MR
(MAX823/MAX825
ONLY)
WDI
(MAX823/MAX824
ONLY)
WATCHDOG
TRANSITION
DETECTOR
WATCHDOG
TIMER
GND
Figure 1. Functional Diagram
6
_______________________________________________________________________________________
5-Pin Microprocessor Supervisory Circuits With
Watchdog Timer and Manual Reset
RESET Output
A microprocessor’s (µP’s) reset input starts the µP in a
known state. The MAX823/MAX824/MAX825 µP supervisory 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 threshold, 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.
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 toggling 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 unconnected 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 unconnected, the maximum allowable leakage current is
10µA and the maximum allowable load capacitance is
200pF.
Manual Reset Input (MAX823/MAX825)
Applications Information
Many µP-based products require manual reset capability, 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 52kΩ pullup
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 function; 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.
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
VCC
1V
Watchdog Input Current
VRST
VRST
tRST
1V
RESET*
RESET
tRP
tRD
RESET
tRP
tRD
tRP
tWD
tRP
WDI
GND
*RESET ON THE MAX824/MAX825 IS THE INVERSE OF RESET.
Figure 2. Reset Timing Diagram
Figure 3. MAX823/MAX824 Watchdog Timing Relationship
_______________________________________________________________________________________
7
MAX823/MAX824/MAX825
_______________Detailed Description
MAX823/MAX824/MAX825
5-Pin Microprocessor Supervisory Circuits With
Watchdog Timer and Manual Reset
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 shortduration, 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, powerdown, 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 negative-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-highlow. 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 beginning of the program, set low at the beginning of every
subroutine or loop, then set high again when the program 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.
VCC
START
VCC
SET WDI
HIGH
VCC
MAX823
MAX824
MAX825
ISOURCE MAX = 800µA L, M
400µA T, S, R, Z, Y
RESET
GENERATOR
VCC
PROGRAM
CODE
RESET
µP
SUBROUTINE OR
PROGRAM LOOP
SET WDI LOW
GND
GND
RETURN
Figure 4. Interfacing to µPs with Bidirectional Resets
8
Figure 5. Watchdog Flow Diagram
_______________________________________________________________________________________
5-Pin Microprocessor Supervisory Circuits With
Watchdog Timer and Manual Reset
____________________Chip Information
TRANSISTOR COUNT: 607
VCC
VCC
PROCESS TECHNOLOGY: BiCMOS
VCC
RESET
RESET
MAX823
µP
WDI
I/O
MR
MANUAL
RESET
GND
GND
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.
Marking Information
MARKING INFORMATION (TOP)
XXXX
(SC70 ONLY)
MARKING INFORMATION (TOP)
XXXX
(SOT ONLY)
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
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
_______________________________________________________________________________________
9
MAX823/MAX824/MAX825
Typical Operating Circuit
5-Pin Microprocessor Supervisory Circuits With
Watchdog Timer and Manual Reset
SC70, 5L.EPS
SOT5L.EPS
MAX823/MAX824/MAX825
Package Information
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
© 2001 Maxim Integrated Products
Printed USA
is a registered trademark of Maxim Integrated Products.