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19-0487; Rev 4; 7/01
5-Pin Microprocessor Supervisory Circuits With Watchdog Timer and Manual Reset
________________General Description
The MAX823/MAX824/MAX825* microprocessor (P) 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.
*Patents Pending
Features
o Precision Monitoring of +2.5V, +3V, +3.3V, and +5V Power Supplies o Operating Current: 6A (MAX823L/M) (SC70) 2A (MAX825T/S/R/Z/Y) (SC70) o Fully Specified Over Temperature o 140ms min Power-On Reset o Guaranteed RESET Valid to VCC = 1V o Power-Supply Transient Immunity o Watchdog Timer with 1.6s Timeout (MAX823/MAX824) o Manual Reset Input (MAX823/MAX825) o No External Components
MAX823/MAX824/MAX825
Ordering Information
PART MAX823_EXK-T MAX823_EUK-T MAX824_EXK-T TEMP. RANGE -40C to +85C -40C to +125C -40C to +85C PIN-PACKAGE 5 SC70-5 5 SOT23-5 5 SC70-5
________________________Applications
Computers and Controllers Embedded Controllers Intelligent Instruments Automotive Systems Critical P Monitoring Portable/Battery-Powered Equipment
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. Ordering Information continued at end of data sheet.
Reset Threshold Table
SUFFIX L M T S R Z (SC70 only) Y (SC70 only) RESET THRESHOLD (V) 4.63 4.38 3.08 2.93 2.63 2.32 2.19
______________________Selector Guide
FUNCTION Active-Low Reset Active-High Reset Watchdog Input Manual Reset Input MAX823 -- MAX824 -- MAX825 --
Typical Operating Circuit appears at end of data sheet. Marking Information appears at end of data sheet.
Pin Configurations
TOP VIEW
RESET 1 5 VCC RESET 1 5 VCC RESET 1 5 VCC
GND 2
MAX823
GND 2
MAX824
GND 2
MAX825
MR 3
4
WDI
RESET 3
4 WDI
RESET 3
4
MR
SOT23/SC70
SOT23/SC70
SOT23/SC70
________________________________________________________________ Maxim Integrated Products
1
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5-Pin Microprocessor Supervisory Circuits With Watchdog Timer and Manual Reset MAX823/MAX824/MAX825
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 = +70C) 5-Pin SC70 (derate 3.1mW/C above +70C) ...............247mW 5-Pin SOT23 (derate 7.1mW/C above +70C).............571mW Operating Temperature Range MAX82_EXK......................................................-40C to +85C MAX82_EUK ...................................................-40C to +125C Storage Temperature Range .............................-65C to +150C Lead Temperature (soldering, 10s) .................................+300C
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 = -40C to +85C (SC70), TA = -40C to +125C (SOT23), unless otherwise noted. Typical values are at TA = +25C.) (Note 1) PARAMETER Operating Voltage Range SYMBOL VCC CONDITIONS TA = 0C to +70C TA = TMIN to TMAX WDI and MR unconnected MAX823L/M MAX824L/M MAX823T/S/R/Z/Y MAX824T/S/R/Z/Y MAX825L/M MAX825T/S/R/Z/Y MAX823L/M MAX824L/M MAX823T/S/R/Z/Y MAX824T/S/R/Z/Y MAX825L/M MAX825T/S/R/Z/Y TA = +25C TA = TMIN to TMAX TA = +25C TA = TMIN to TMAX TA = +25C TA = TMIN to TMAX TA = +25C TA = TMIN to TMAX TA = +25C TA = TMIN to TMAX TA = +25C TA = TMIN to TMAX TA = +25C TA = TMIN to TMAX 4.56 4.50 4.31 4.25 3.04 3.00 2.89 2.85 2.59 2.55 2.28 2.25 2.16 2.13 2.19 2.32 2.63 2.93 3.08 4.38 MIN 1.0 1.2 10 5 4.5 3 6 4 3 2 4.63 24 12 12 8 17 12 8 6 4.70 4.75 4.45 4.50 3.11 3.15 2.96 3.00 2.66 2.70 2.35 2.38 2.22 2.25 V A A TYP MAX 5.5 UNITS V
Supply Current (SOT23 Only)
ISUPPLY
MR unconnected
Supply Current (SC70 Only)
ISUPPLY
WDI and MR unconnected
MR unconnected MAX82_L MAX82_M MAX82_T Reset Threshold VRST MAX82_S MAX82_R MAX82_Z (SC70 only) MAX82_Y (SC70 only)
2
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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 = -40C to +85C (SC70), TA = -40C to +125C (SOT23), unless otherwise noted. Typical values are at TA = +25C.) (Note 1)
PARAMETER Reset Threshold Hysteresis Reset Threshold Temperature Coefficient Reset Timeout Period VCC to RESET Delay tRP VRST - VCC = 100mV MAX82_L/M, VCC = VRST max, ISOURCE = 120A MAX82_T/S/R/Z/Y, VCC = VRST max, ISOURCE = 30A MAX82_L/M, VCC = VRST min, ISINK = 3.2mA MAX82_T/S/R/Z/Y VCC = VRST min, ISINK = 1.2mA TA = 0C to +70C, VCC = 1V, VCC falling, ISINK = 50A TA = TMIN to TMAX, VCC = 1.2V, VCC falling, VBATT = 0V, ISINK = 100A RESET Output Short-Circuit Current (Note 2) ISOURCE VOH RESET Output Voltage MAX82_L/M, RESET = 0V, VCC = 5.5V MAX82_T/S/R/Z/Y, RESET = 0V, VCC = 3.6V VCC > 1.8V, ISOURCE = 150A MAX824L/M, MAX825L/M, VCC = VRST max, ISINK = 3.2mA MAX824T/S/R/Z/Y, MAX825T/S/R/Z/Y, VCC = VRST max, ISINK = 1.2mA 1.12 VIL = 0.4V, VIH = 0.8 VCC 50 0.3 VCC 0.7 VCC WDI = VCC, time average WDI = 0, time average -20 120 -15 160 1.60 0.8 VCC 0.4 0.3 V 800 400 A VCC - 1.5 0.8 VCC 0.4 V 0.3 0.3 140 SYMBOL MAX82_L/M MAX82_T/S/R/Z/Y CONDITIONS MIN TYP 10 5 40 200 20 280 MAX UNITS mV ppm/C ms s
MAX823/MAX824/MAX825
VOH
RESET Output Voltage VOL
VOL
WATCHDOG INPUT (MAX823/MAX824) Watchdog Timeout Period WDI Pulse Width WDI Input Voltage (Note 3) WDI Input Current (Note 4) tWD tWDI VIL VIH 2.40 s ns V A
_______________________________________________________________________________________
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5-Pin Microprocessor Supervisory Circuits With Watchdog Timer and Manual Reset MAX823/MAX824/MAX825
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 = -40C to +85C (SC70), TA = -40C to +125C (SOT23), unless otherwise noted. Typical values are at TA = +25C.) (Note 1)
PARAMETER SYMBOL VIL VIH 0.7 VCC 1.0 100 500 35 52 75 CONDITIONS MIN TYP MAX UNITS MANUAL RESET INPUT (MAX823/MAX825) MR Input Voltage MR Pulse Width MR Noise Immunity (pulse width with no reset) MR to Reset Delay MR Pullup Resistance (internal) 0.3 VCC V s ns ns k
Note 1: Note 2: Note 3: Note 4:
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 P 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 10A maximum leakage current and a maximum capacitive load of 200pF. This output device must be able to source and sink at least 200A when active.
4
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5-Pin Microprocessor Supervisory Circuits With Watchdog Timer and Manual Reset
__________________________________________Typical Operating Characteristics
MAX823_, VCC = +5V, TA = +25C, unless otherwise noted.)
MAX823/MAX824/MAX825
VCC SUPPLY CURRENT vs. TEMPERATURE
MAX823/4/5 toc01
RESET TIMEOUT PERIOD vs. TEMPERATURE
MAX823/4/5 toc02
RESET COMPARATOR PROPAGATION DELAY vs. TEMPERATURE
VCC FALLING PROPAGATION DELAY (s) 25 20 15 10 5 0
MAX823/4/5 toc03
9 (SC70 ONLY) 8 SUPPLY CURRENT (A) 7 6 5 4 3 MAX825R 2 1 -40 -20 0 20 40 60 80 100 120 TEMPERATURE (C) MAX824Y MAX823L
250 240 RESET TIMEOUT PERIOD (ms) 230 220 210 200 190 180 170 160 150 -40 -20 0 20 40 60 80
30
100
-40
-20
0
20
40
60
80
100
TEMPERATURE (C)
TEMPERATURE (C)
WATCHDOG TIMEOUT PERIOD vs. TEMPERATURE
MAX823/4/5 toc04
NORMALIZED RESET THRESHOLD VOLTAGE vs. TEMPERATURE
MAX823/4/5 toc05
MAXIMUM VCC TRANSIENT DURATION vs. RESET THRESHOLD OVERDRIVE
45 TRANSIENT DURATION (s) 40 35 30 25 20 15 10 5 MAX82_L 0 20 40 60 80 100 120 140 160 180 200 RESET OCCURS ABOVE CURVE MAX82_Y MAX82_R (SC70 ONLY)
MAX823/4/5 toc06
2.0 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
1.06 NORMALIZED RESET THRESHOLD (V) 1.04 1.02 1.00 0.98 0.96 0.94
50
0 -40 -20 0 20 40 60 80 100 TEMPERATURE (C) RESET THRESHOLD OVERDRIVE (mV), VRST - VCC
100
TEMPERATURE (C)
_______________________________________________________________________________________
5
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. 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 52k 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. 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. Supply Voltage
1
1
1
RESET
2
2
2
GND
3
--
4
MR
--
3
3
RESET
4
4
--
WDI
5
5
5
VCC
VCC
MAX823 MAX824 MAX825
RESET GENERATOR VCC 1.25V RESET RESET (MAX824/MAX825 ONLY)
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
_______________Detailed Description
RESET Output
A microprocessor's (P's) reset input starts the P in a known state. The MAX823/MAX824/MAX825 P 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 P's activity. If the P 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 10A and the maximum allowable load capacitance is 200pF.
MAX823/MAX824/MAX825
Manual Reset Input (MAX823/MAX825)
Many P-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 52k 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 0.1F capacitor from MR to GND to provide additional noise immunity.
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 160A can flow into WDI.
VCC 1V VRST VRST 1V
VCC tRST RESET*
RESET
tRP
tRD
tRP
tWD
tRP
RESET GND
tRP
tRD
WDI
*RESET ON THE MAX824/MAX825 IS THE INVERSE OF RESET.
Figure 2. Reset Timing Diagram
Figure 3. MAX823/MAX824 Watchdog Timing Relationship 7
_______________________________________________________________________________________
5-Pin Microprocessor Supervisory Circuits With Watchdog Timer and Manual Reset MAX823/MAX824/MAX825
Interfacing to Ps with Bidirectional Reset Pins
The RESET output maximum pullup current is 800A for L/M versions (400A for T/S/R/Z/Y versions). This allows Ps with bidirectional resets, such as the 68HC11, to force RESET low when the MAX823/MAX824/MAX825 are pulling RESET high (Figure 4). An optional 0.1F 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.
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 P 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.
VCC
START
VCC VCC
SET WDI HIGH PROGRAM CODE
MAX823 MAX824 MAX825
RESET GENERATOR
ISOURCE MAX = 800A L, M 400A T, S, R, Z, Y
VCC
RESET
P
SUBROUTINE OR PROGRAM LOOP SET WDI LOW
GND GND
RETURN
Figure 4. Interfacing to Ps with Bidirectional Resets 8
Figure 5. Watchdog Flow Diagram
_______________________________________________________________________________________
5-Pin Microprocessor Supervisory Circuits With Watchdog Timer and Manual Reset
Typical Operating Circuit
VCC VCC VCC RESET RESET
____________________Chip Information
TRANSISTOR COUNT: 607 PROCESS TECHNOLOGY: BiCMOS
MAX823/MAX824/MAX825
MAX823
WDI MANUAL RESET MR I/O
P
GND GND
Ordering Information (continued)
PART MAX824_EUK-T MAX825_EXK-T MAX825_EUK-T TEMP. RANGE -40C to +125C -40C to +85C -40C to +125C PIN-PACKAGE 5 SOT23-5 5 SC70-5 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
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5-Pin Microprocessor Supervisory Circuits With Watchdog Timer and Manual Reset MAX823/MAX824/MAX825
Package Information
SOT5L.EPS
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 (c) 2001 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.
SC70, 5L.EPS

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