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19-1868; Rev 1; 1/01
Low-Voltage SOT23 P Supervisors with Manual Reset and Watchdog Timer
General Description
The MAX6821-MAX6825 are low-voltage microprocessor (P) supervisory circuits that combine voltage monitoring, watchdog timer, and manual reset input functions in a 5-pin SOT23 package. Microprocessor supervisory circuits significantly improve system reliability and accuracy compared to separate ICs or discrete components. These devices assert a reset signal whenever the monitored voltage drops below its preset threshold, keeping it asserted for a minimum timeout period after VCC 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 voltages from +1.8V to +5.0V. These outputs are guaranteed to be in the correct state for VCC down to +1.0V. Nine preprogrammed reset threshold voltages are available (see 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 pushpull 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 VCC = +1.0V o Immune to Short Negative VCC 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 -40C to +125C -40C to +125C -40C to +125C -40C to +125C -40C to +125C 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 P Monitoring Portable/BatteryPowered Equipment
*Insert the desired suffix letter (from the table below) into the blank to complete the part number.
Threshold Suffix Guide
SUFFIX L RESET THRESHOLD (V) 4.63 4.38 3.08 2.93 2.63 2.32 2.19 1.67 1.58
Pin Configurations
TOP VIEW
RESET(RESET) 1 5 VCC
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 price, delivery, and to place orders, please contact Maxim Distribution at 1-888-629-4642, or visit Maxim's website at www.maxim-ic.com.
Low-Voltage SOT23 P Supervisors with Manual Reset and Watchdog Timer MAX6821-MAX6825
ABSOLUTE MAXIMUM RATINGS
VCC to GND ...........................................................-0.3V to +6.0V Open-Drain RESET................................................-0.3V to +6.0V Push-Pull RESET, RESET, MR, WDI ...........-0.3V to (VCC + 0.3V) Input Current (VCC) .............................................................20mA Output Current (RESET, RESET).........................................20mA Continuous Power Dissipation (TA = +70C) 5-Pin SOT23 (derate 7.1mW/C above +70C)............571mW Operating Temperature Range .........................-40C to +125C Junction Temperature ......................................................+150C 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 = +4.5V to +5.5V for MAX682_L/M, VCC = +2.7V to +3.6V for MAX682_T/S/R, VCC = +2.1V to +2.75V for MAX682_Z/Y, VCC = +1.53V to +2.0V for MAX682_W/V, TA = -40C to +125C, unless otherwise specified. Typical values are at TA = +25C.) (Note 1)
PARAMETER Operating Voltage Range SYMBOL VCC CONDITIONS TA = 0C to +85C TA = -40C to +125C VCC = +5.5V, no load VCC Supply Current (MR and WDI Unconnected) ICC VCC = +3.6V, no load VCC = +3.6V, no load (MAX6825 only) MAX682_L MAX682_M MAX682_T MAX682_S VCC Reset Threshold (VCC Falling) VTH MAX682_R MAX682_Z MAX682_Y MAX682_W MAX682_V Reset Threshold Temperature Coefficient Reset Threshold Hysteresis VCC to Reset Output Delay tRD VCC = VTH to (VTH - 100mV) TA = -40C to +85C TA = -40C to +125C TA = -40C to +85C TA = -40C to +125C TA = -40C to +85C TA = -40C to +125C TA = -40C to +85C TA = -40C to +125C TA = -40C to +85C TA = -40C to +125C TA = -40C to +85C TA = -40C to +125C TA = -40C to +85C TA = -40C to +125C TA = -40C to +85C TA = -40C to +125C TA = -40C to +85C TA = -40C to +125C TA = -40C to +85C TA = -40C to +125C TA = -40C to +85C TA = -40C to +125C TA = -40C to +85C 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 VTH 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 s V A UNITS V
2
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Low-Voltage SOT23 P Supervisors with Manual Reset and Watchdog Timer
ELECTRICAL CHARACTERISTICS (continued)
(VCC = +4.5V to +5.5V for MAX682_L/M, VCC = +2.7V to +3.6V for MAX682_T/S/R, VCC = +2.1V to +2.75V for MAX682_Z/Y, VCC = +1.53V to +2.0V for MAX682_W/V, TA = -40C to +125C, unless otherwise specified. Typical values are at TA = +25C.) (Note 1)
PARAMETER Reset Timeout Period SYMBOL tRP CONDITIONS TA = -40C to +85C TA = -40C to +125C VCC 1.0V, ISINK = 50A, reset asserted, TA = 0C to +85C VOL VCC 1.2V, ISINK = 100A, reset asserted VCC 2.55V, ISINK = 1.2mA, reset asserted VCC 4.25V, ISINK = 3.2mA, reset asserted VCC 1.8V, ISOURCE = 200A, reset not asserted RESET Output HIGH (Push-Pull Only) VOH VCC 3.15V, ISOURCE = 500A, reset not asserted VCC 4.75V, ISOURCE = 800A, reset not asserted Open-Drain RESET Output Leakage Current (Note 1) ILKG VCC > VTH, RESET not asserted VCC 1.0V, ISOURCE = 1A, reset asserted, TA = 0C to +85C RESET Output HIGH (Push-Pull Only) VOH VCC 1.50V, ISOURCE = 100A, reset asserted VCC 2.55V, ISOURCE = 500A, reset asserted VCC 4.25V, ISOURCE = 800A, reset asserted RESET Output LOW (Push-Pull Only) VCC 1.8V, ISINK = 500A, reset not asserted VOL VCC 3.15V, ISINK = 1.2mA, reset not asserted VCC 4.75V, ISINK = 3.2mA, reset not asserted VIL VIH 0.7 VCC 1 100 200 25 TA = -40C to +85C TA = -40C to +125C 1.12 0.80 50 0.3 VCC 0.7 VCC WDI = VCC, time average WDI = 0, time average -20 120 -15 160 50 1.60 75 2.40 2.60 0.8 VCC 0.8 VCC 0.8 VCC 0.8 VCC 0.3 0.3 0.4 0.3 VCC V V 0.8 VCC 0.8 VCC 0.8 VCC 1.0 A 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 tWD tWDI VIL VIH IWDI s ns V A V s ns ns k
Note 1: Over-temperature limits are guaranteed by design and not production tested. Devices tested at TA = +25C. Note 2: Guaranteed by design and not production tested. _______________________________________________________________________________________ 3
Low-Voltage SOT23 P Supervisors with Manual Reset and Watchdog Timer MAX6821-MAX6825
Typical Operating Characteristics
(TA = +25C, unless otherwise noted.)
SUPPLY CURRENT vs. TEMPERATURE
MAX6821 toc01
RESET TIMEOUT PERIOD vs. TEMPERATURE
MAX6821 toc02
VCC TO RESET OUTPUT DELAY vs. TEMPERATURE
VCC FALLING, VCC = VTH - 100mV
MAX6821 toc03
13 12 11 SUPPLY CURRENT (A) 10 9 8 7 6 5 4 3 -40 -20 0 20 40 60 80 100 120 TEMPERATURE (C) VCC = +3.3V, S VERSION VCC = +1.8V, V VERSION VCC = +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 (s) 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 VCC 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 (s)
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), VTH - VCC
TEMPERATURE (C)
VOLTAGE OUTPUT LOW vs. ISINK
MAX6821 toc07
VOLTAGE OUTPUT HIGH vs. ISOURCE
VCC = +2.9V 2.90 2.88 2.86 VOUT (V) 2.84 2.82 2.80
MAX6821 toc08
0.35 0.30 0.25 VOUT (V) 0.20 0.15 0.10
VCC = +2.9V
2.92
2.78 0.05 0 0 1 2 3 4 5 6 7 ISINK (mA) 2.76 2.74 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 ISOURCE (mA)
4
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Low-Voltage SOT23 P 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 VCC 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 VCC 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 VCC 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 VCC exceeds the device reset threshold, MR goes low to high, or the watchdog triggers a reset. Ground Active-Low Manual Reset Input. Internal 50k pullup to VCC. 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 VCC 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
VCC
Detailed Description
RESET/RESET Output
A P's reset input starts the P in a known state. The MAX6821-MAX6825 P supervisory circuits assert a reset to prevent code-execution errors during powerup, power-down, and brownout conditions. Whenever VCC falls below the reset threshold, the reset output asserts low for RESET and high for RESET. Once VCC exceeds the reset threshold, an internal timer keeps the reset output asserted for the specified reset timeout period (tRP); after this interval, reset output returns to its original state (see Figure 2).
returns high. MR has an internal 50k 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.
Watchdog Input
In the MAX6821-MAX6824, the watchdog circuit monitors the P's activity. If the P 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 P-based products require manual reset capability, 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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Low-Voltage SOT23 P Supervisors with Manual Reset and Watchdog Timer MAX6821-MAX6825
VCC
MAX6821- MAX6825
RESET (MAX6822- MAX6825) RESET (MAX6821/MAX6824/ MAX6825)
RESET GENERATOR VCC 1.26V
MR (MAX6821/MAX6822/MAX6823, MAX6825) WDI (MAX6821- MAX6824) WATCHDOG TRANSITION DETECTOR WATCHDOG TIMER
GND
Figure 1. Functional Diagram
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.
VCC 1V VTH VTH 1V
RESET
tRP
tRD
RESET GND
tRP
tRD
Applications Information
Watchdog Input Current
The MAX6821/MAX6822/MAX6823/MAX6824 WDI inputs are internally driven through a buffer and series resistor from the watchdog timer (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.
6
Figure 2. Reset Timing Diagram
Interfacing to Ps with Bidirectional Reset Pins
Since the RESET output on the MAX6822 is open drain, it interfaces easily with Ps that have bidirectional reset pins, such as the Motorola 68HC11. Connecting the P supervisor's RESET output directly to the microcontroller's RESET pin with a single pullup resistor allows either device to assert reset (see 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.
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Low-Voltage SOT23 P Supervisors with Manual Reset and Watchdog Timer MAX6821-MAX6825
VCC tRST RESET* tRP tWD tRP RESET GENERATOR GND *RESET IS THE INVERSE OF RESET. VCC VCC
MAX6822
RESET RESET
P
GND
WDI
Figure 3. Watchdog Timing Relationship
Figure 4. Interfacing Open-Drain RESET to Ps with Bidirectional Reset I/O
Resets are issued to the P during power-up, powerdown, and brownout conditions. The Typical Operating Characteristics show a graph of the MAX6821- MAX6825's Maximum VCC Transient Duration vs. Reset Threshold Overdrive, for which reset pulses are not generated. The graph was produced using negativegoing VCC pulses, starting at the standard monitored voltage and ending below the reset threshold by the magnitude indicated (reset threshold overdrive). The graph shows the maximum pulse width that a negativegoing 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. Typically, a VCC transient that goes 100mV below the reset threshold and lasts for 20s or less will not trigger a reset pulse.
START
SET WDI HIGH PROGRAM CODE
SUBROUTINE OR PROGRAM LOOP SET WDI LOW
Watchdog Software Considerations
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.
RETURN
Figure 5. Watchdog Flow Diagram
Typical Operating Circuit
VCC VCC VCC RESET RESET
MAX6823
WDI MANUAL RESET MR GND I/O
P
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7
Low-Voltage SOT23 P Supervisors with Manual Reset and Watchdog Timer MAX6821-MAX6825
Selector Guide
FUNCTION MAX6821 MAX6822 MAX6823 MAX6824 MAX6825 ACTIVE-LOW RESET -- -- ACTIVE-HIGH RESET -- -- OPEN-DRAIN RESET -- -- -- -- WATCHDOG INPUT -- MANUAL RESET INPUT --
Pin Configurations (continued)
TOP VIEW
RESET 1 5 VCC RESET 1 5 VCC
GND 2
MAX6824
GND 2
MAX6825
RESET 3
4
WDI
RESET 3
4
MR
SOT23-5
SOT23-5
Chip Information
TRANSISTOR COUNT: 750 PROCESS: BiCMOS
8
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Low-Voltage SOT23 P Supervisors with Manual Reset and Watchdog Timer
Package Information
SOT5L.EPS
MAX6821-MAX6825
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.
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 _____________________ 9 (c) 2001 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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