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19-1676; Rev 2; 2/03
Pin-Selectable Watchdog Timers
General Description
The MAX6369-MAX6374 are pin-selectable watchdog timers that supervise microprocessor (P) activity and signal when a system is operating improperly. During normal operation, the microprocessor should repeatedly toggle the watchdog input (WDI) before the selected watchdog timeout period elapses to demonstrate that the system is processing code properly. If the P does not provide a valid watchdog input transition before the timeout period expires, the supervisor asserts a watchdog (WDO) output to signal that the system is not executing the desired instructions within the expected time frame. The watchdog output pulse can be used to reset the P or interrupt the system to warn of processing errors. The MAX6369-MAX6374 are flexible watchdog timer supervisors that can increase system reliability through notification of code execution errors. The family offers several pin-selectable watchdog timing options to match a wide range of system timing applications: * Watchdog startup delay: provides an initial delay before the watchdog timer is started. * Watchdog timeout period: normal operating watchdog timeout period after the initial startup delay. * Watchdog output/timing options: open drain (100ms) or push-pull (1ms). The MAX6369-MAX6374 operate over a +2.5V to +5.5V supply range and are available in miniature 8-pin SOT23 packages.
Features
o Precision Watchdog Timer for Critical P Applications o Pin-Selectable Watchdog Timeout Periods o Pin-Selectable Watchdog Startup Delay Periods o Ability to Change Watchdog Timing Characteristics Without Power Cycling o Open-Drain or Push-Pull Pulsed Active-Low Watchdog Output o Watchdog Timer Disable Feature o +2.5V to +5.5V Operating Voltage o 8A Low Supply Current o No External Components Required o Miniature 8-Pin SOT23 Package
MAX6369-MAX6374
Ordering Information
PART MAX6369KA-T MAX6370KA-T MAX6371KA-T MAX6372KA-T MAX6373KA-T MAX6374KA-T TEMP RANGE -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C PINPACKAGE 8 SOT23-8 8 SOT23-8 8 SOT23-8 8 SOT23-8 8 SOT23-8 8 SOT23-8 TOP MARKS AADC AADD AADE AADF AADG AADH
________________________Applications
Embedded Control Systems Industrial Controllers Critical P and Microcontroller (C) Monitoring Automotive Telecommunications Networking
Note: All devices are available in tape-and-reel only. Required order increment is 2,500 pieces.
Pin Configuration appears at end of data sheet.
Selector Guide
PART MAX6369 MAX6370 MAX6371 MAX6372 MAX6373 MAX6374 OUTPUT Open Drain Push-Pull Open Drain Push-Pull Open Drain Push-Pull WDO PULSE WIDTH (ms) 100 1 100 1 100 1 MINIMUM STARTUP DELAY Selectable: 1ms to 60s Selectable: 1ms to 60s 60s 60s Selectable: 200s to 60s or first edge Selectable: 200s to 60s or first edge MINIMUM WATCHDOG TIMEOUT Selectable: 1ms to 60s Selectable: 1ms to 60s Selectable: 1ms to 60s Selectable: 1ms to 60s Selectable: 30s to 10s Selectable: 30s to 10s
________________________________________________________________ Maxim Integrated Products
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Pin-Selectable Watchdog Timers MAX6369-MAX6374
ABSOLUTE MAXIMUM RATINGS
Terminal Voltage (with respect to GND) VCC .....................................................................-0.3V to +6V WDI.....................................................................-0.3V to +6V WDO (Open Drain: MAX6369/71/73) .................-0.3V to +6V WDO (Push-Pull: MAX6370/72/74 .......-0.3V to (VCC + 0.3V) SET0, SET1, SET2 ................................-0.3V to (VCC + 0.3V) Maximum Current, Any Pin (input/output)...........................20mA Continuous Power Dissipation (TA = +70C) SOT23-8 (derate 8.75mW/C above +70C)...............700mW Operating Temperature Range ...........................-40C to +85C Storage Temperature Range .............................-65C to +150C Junction Temperature ......................................................+150C Lead Temperature (soldering, 10s) .................................+300C VCC Rise or Fall Rate......................................................0.05V/s
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 = +2.5V to +5.5V, SET_ = VCC or GND, TA = -40C to +85C, unless otherwise noted. Typical values are at TA = +25C and VCC = +3V.) (Note 1)
PARAMETER Operating Voltage Range Supply Current Input High Voltage Input Low Voltage Logic Input Current (Note 2) WDO Output Low Voltage SYMBOL VCC ICC VIH VIL No load WDI, SET0, SET1, SET2 WDI, SET0, SET1, SET2 WDI or SET_ = 0 or VCC ISINK = 1.2mA, VCC > 2.7V, watchdog output asserted VOL ISINK = 6mA, VCC > 4.5V, watchdog output asserted V NDO = 0 to +5.5V, output deasserted, MAX6369/MAX6371/MAX6373 ISOURCE = 500A, VCC > 2.7V, watchdog output deasserted VOH ISOURCE = 800A, VCC > 4.5V, watchdog output deasserted SET2 = 0, SET1 = 0, SET0 = 0 SET2 = 0, SET1 = 0, SET0 = VCC SET2 = 0, SET1 = VCC, SET0 = 0 SET2 = 0, SET1 = VCC, SET0 = VCC Startup Delay Period tDELAY SET2 = VCC, SET1 = 0, SET0 = 0 SET2 = VCC, SET1 = 0, SET0 = VCC SET2 = VCC, SET1 = VCC, SET0 = 0 SET2 = VCC, SET1 = VCC, SET0 = VCC 0.8 x VCC V VCC - 1.5 VCC 3.3V VCC 2.5V 0 0.8 x VCC 0.8 0.6 10 0.3 0.4 1 CONDITIONS MIN 2.5 8 TYP MAX 5.5 20 UNITS V A V V nA V V A
WDO Leakage Current
ILKG
WDO Output High Voltage MAX6369/MAX6370
1 10 30 100 1 10 60
3 30 90 300 3 30 180 s ms ms
Watchdog Disabled
2
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Pin-Selectable Watchdog Timers
ELECTRICAL CHARACTERISTICS (continued)
(VCC = +2.5V to +5.5V, SET_ = VCC or GND, TA = -40C to +85C, unless otherwise noted. Typical values are at TA = +25C and VCC = +3V.) (Note 1)
PARAMETER SYMBOL CONDITIONS SET2 = 0, SET1 = 0, SET0 = 0 SET2 = 0, SET1 = 0, SET0 = VCC SET2 = 0, SET1 = VCC, SET0 = 0 Watchdog Timeout Period tWD SET2 = 0, SET1 = VCC, SET0 = VCC SET2 = VCC, SET1 = 0, SET0 = 0 SET2 = VCC, SET1 = 0, SET0 = VCC SET2 = VCC, SET1 = VCC, SET0 = 0 SET2 = VCC, SET1 = VCC, SET0 = VCC MAX6371/MAX6372 Startup Delay Period tDELAY SET2 = 0, SET1 = VCC, SET0 = VCC All other SET_ conditions SET2 = 0, SET1 = 0, SET0 = 0 SET2 = 0, SET1 = 0, SET0 = VCC SET2 = 0, SET1 = VCC, SET0 = 0 Watchdog Time-Out Period tWD SET2 = 0, SET1 = VCC, SET0 = VCC SET2 = VCC, SET1 = 0, SET0 = 0 SET2 = VCC, SET1 = 0, SET0 = VCC SET2 = VCC, SET1 = VCC, SET0 = 0 SET2 = VCC, SET1 = VCC, SET0 = VCC MAX6373/MAX6374 SET2 = 0, SET1 = 0, SET0 = 0 SET2 = 0, SET1 = 0, SET0 = VCC SET2 = 0, SET1 = VCC, SET0 = 0 Startup Delay Period tDELAY SET2 = 0, SET1 = VCC, SET0 = VCC SET2 = VCC, SET1 = 0, SET0 = 0 SET2 = VCC, SET1 = 0, SET0 = VCC SET2 = VCC, SET1 = VCC, SET0 = 0 SET2 = VCC, SET1 = VCC, SET0 = VCC SET2 = 0, SET1 = 0, SET0 = 0 SET2 = 0, SET1 = 0, SET0 = VCC SET2 = 0, SET1 = VCC, SET0 = 0 Watchdog Timeout Period tWD SET2 = 0, SET1 = VCC, SET0 = VCC SET2 = VCC, SET1 = 0, SET0 = 0 SET2 = VCC, SET1 = 0, SET0 = VCC SET2 = VCC, SET1 = VCC, SET0 = 0 SET2 = VCC, SET1 = VCC, SET0 = VCC 3 3 60 200 9 9 180 600 ms s Watchdog Disabled 60 1 3 10 100 300 3 60 180 3 9 30 300 900 9 180 ms s MIN 1 10 30 100 1 10 60 TYP MAX 3 30 90 300 3 30 180 s ms ms UNITS
MAX6369-MAX6374
Watchdog Disabled
Watchdog Disabled ms s
Watchdog Disabled s First Edge (Note 3) First Edge (Note 3) 60 3 3 1 30 1 10 10 180 9 9 3 90 3 30 30 s s ms s
Watchdog Disabled s
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Pin-Selectable Watchdog Timers MAX6369-MAX6374
ELECTRICAL CHARACTERISTICS (continued)
(VCC = +2.5V to +5.5V, SET_ = VCC or GND, TA = -40C to +85C, unless otherwise noted. Typical values are at TA = +25C and VCC = +3V.) (Note 1)
PARAMETER Watchdog Input Pulse Width (Note 2) Watchdog Output Pulse Width Internal Setup Time (Note 4) SYMBOL tWDI tWDO tSETUP CONDITIONS After WDO deasserted MAX6369/MAX6371/MAX6373 MAX6370/MAX6372/MAX6374 After WDO deasserted MIN 100 100 1 100 300 3 300 TYP MAX UNITS ns ms ms s
Note 1: Production tested at TA = +25C. Guaranteed by design over temperature limits. Note 2: Guaranteed by design. Note 3: In this setting the watchdog timer is inactive and startup delay ends when WDI sees its first level transition. See Selecting Device Timing for more information. Note 4: After power-up, or a setting change, there is an internal setup time during which WDI is ignored.
Typical Operating Characteristics
(Circuit of Figure 1, TA = +25C, unless otherwise noted.)
SUPPLY CURRENT vs. TEMPERATURE
MAX6369/74-01
WATCHDOG TIMEOUT PERIOD vs. TEMPERATURE
NORMALIZED WATCHDOG TIMEOUT PERIOD
MAX6369/74-02
14
1.003 1.002 1.001 1.000 0.999 0.998 0.997
12 SUPPLY CURRENT (A) VCC = +5.5V 10
8 VCC = +2.5V 6
4 -40 -15 10 35 60 85 TEMPERATURE (C)
-40
-15
10
35
60
85
TEMPERATURE (C)
4
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Pin-Selectable Watchdog Timers
Pin Description
PIN 1 2 3 4 5 6 7 8 NAME WDI GND N.C. SET0 SET1 SET2 WDO VCC FUNCTION Watchdog Input. If WDI remains either high or low for the duration of the watchdog timeout period (tWD), WDO triggers a pulse. The internal watchdog timer clears whenever a WDO is asserted or whenever WDI sees a rising or falling edge. Ground Not Connected. Do not make any connection to this pin. Set Zero. Logic input for selecting startup delay and watchdog timeout periods. See Table 1 for timing details. Set One. Logic input for selecting startup delay and watchdog timeout periods. See Table 1 for timing details. Set Two. Logic input for selecting startup delay and watchdog timeout periods. See Table 1 for timing details. Watchdog Output. Pulses low for the watchdog output pulse width, tWDO, when the internal watchdog times out. The MAX6369/MAX6371/MAX6373 have open-drain outputs and require a pull-up resistor. The MAX6370/MAX6372/MAX6374 outputs are push-pull. Supply Voltage (+2.5V to +5.5V)
MAX6369-MAX6374
Table 1. Minimum Timeout Settings
LOGIC INPUTS SET2 0 0 0 0 1 1 1 1 SET1 0 0 1 1 0 0 1 1 SET0 0 1 0 1 0 1 0 1 MAX6369/MAX6370 tDELAY, tWD 1ms 10ms 30ms Disabled 100ms 1s 10s 60s MAX6371/MAX6372 tDELAY = 60s, tWD 1ms 3ms 10ms Disabled 100ms 300ms 3s 60s MAX6373/MAX6374 tDELAY 3ms 3s 60s Disabled 200s First Edge First Edge 60s tWD 3ms 3s 1s Disabled 30s 1s 10s 10s
Detailed Description
The MAX6369-MAX6374 are flexible watchdog circuits for monitoring P activity. During normal operation, the internal timer is cleared each time the P toggles the WDI with a valid logic transition (low to high or high to low) within the selected timeout period (tWD). The WDO remains high as long as the input is strobed within the selected timeout period. If the input is not strobed before the timeout period expires, the watchdog output is asserted low for the watchdog output pulse width (tWDO). The device type and the state of the three logic control pins (SET0, SET1, and SET2) determine watchdog timing characteristics. The three basic timing variations for the watchdog startup delay and the normal
watchdog timeout period are summarized below (see Table 1 for the timeout characteristics for all devices in the family): * Watchdog Startup Delay: Provides an initial delay before the watchdog timer is started. Allows time for the P system to power up and initialize before assuming responsibility for normal watchdog timer updates. Includes several fixed or pin-selectable startup delay options from 200s to 60s, and an option to wait for the first watchdog input transition before starting the watchdog timer.
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Pin-Selectable Watchdog Timers MAX6369-MAX6374
VCC WDI
MAX6369-MAX6374
TRANSITION DETECTOR
EN
SET 2 SET 1 SET 0 CONTROL LOGIC ENABLE
CLEAR SET WATCHDOG TIMEOUT SET STARTUP DELAY WATCHDOG TIMER CIRCUITRY GND OUT OUTPUT WDO
Figure 1. Functional Diagram
VCC
tSETUP
tDELAY
tWD tWD tWD
WDI A WDO A TRANSITIONS ON WDI IGNORED DURING SETUP DELAY. B TRANSITION(S) ON WDI IGNORED DURING STARTUP DELAY PERIOD. C WATCHDOG TIMER STARTS AFTER STARTUP DELAY AND WDO IS DEASSERTED. D TRANSITION OCCURS BEFORE WATCHDOG TIMEOUT PERIOD. WATCHDOG TIMER CLEARS AND STARTS TIMER AGAIN. E WATCHDOG TIMES OUT, WDO ASSERTS. F TRANSITIONS ON WDI IGNORED WHEN WDO ASSERTED. G WATCHDOG TIMER STARTS AFTER WDO DEASSERTS. A B C D EF tWDO G E
Figure 2. Watchdog Timing
* Watchdog Timeout Period: Normal operating watchdog timeout period after the initial startup delay. A watchdog output pulse is asserted if a valid watchdog input transition is not received before the timeout period elapses. Eight pin-selectable timeout period options for each device, from 30s to 60s. Pin-selectable watchdog timer disable feature.
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* Watchdog Output/Timing Options: Open drain, active low with 100ms minimum watchdog output pulse (MAX6369/MAX6371/MAX6373). Push-pull, active low with 1ms minimum watchdog output pulse (MAX6370/MAX6372/MAX6374). Each device has a watchdog startup delay that is initiated when the supervisor is first powered or after the user modifies any of the logic control set inputs. The watchdog timer does not begin to count down until the
_______________________________________________________________________________________
Pin-Selectable Watchdog Timers
completion of the startup delay period, and no watchdog output pulses are asserted during the startup delay. When the startup delay expires, the watchdog begins counting its normal watchdog timeout period and waiting for WDI transitions. The startup delay allows time for the P system to power up and fully initialize before assuming responsibility for the normal watchdog timer updates. Startup delay periods vary between the different devices and may be altered by the logic control set pins. To ensure that the system generates no undesired watchdog outputs, the routine watchdog input transitions should begin before the selected minimum startup delay period has expired. The normal watchdog timeout period countdown is initiated when the startup delay is complete. If a valid logic transition is not recognized at WDI before the watchdog timeout period has expired, the supervisor asserts a watchdog output. Watchdog timeout periods vary between the different devices and may be altered by the logic control set pins. To ensure that the system generates no undesired watchdog outputs, the watchdog input transitions should occur before the selected minimum watchdog timeout period has expired. The startup delay and the watchdog timeout period are determined by the states of the SET0, SET1, and SET2 pins, and by the particular device within the family. For the MAX6369 and MAX6370, the startup delay is equal to the watchdog timeout period. The startup and watchdog timeout periods are pin selectable from 1ms to 60s (minimum). For the MAX6371 and MAX6372, the startup delay is fixed at 60s and the watchdog timeout period is pin selectable from 1ms to 60s (minimum). The MAX6373/MAX6374 provide two timing variations for the startup delay and normal watchdog timeout. Five of the pin-selectable modes provide startup delays from 200s to 60s minimum, and watchdog timeout delays from 3ms to 10s minimum. Two of the selectable modes do not initiate the watchdog timer until the device receives its first valid watchdog input transition (there is no fixed period by which the first input must be received). These two extended startup delay modes are useful for applications requiring more than 60s for system initialization. All the MAX6369-MAX6374 devices may be disabled with the proper logic control pin setting (Table 1).
MAX6369-MAX6374
Applications Information
Input Signal Considerations
Watchdog timing is measured from the last WDI rising or falling edge associated with a pulse of at least 100ns in width. WDI transitions are ignored when WDO is asserted, and during the startup delay period (Figure 2). Watchdog input transitions are also ignored for a setup period, tSETUP, of up to 300s after power-up or a setting change (Figure 3).
Selecting Device Timing
SET2, SET1, and SET0 program the startup delay and watchdog timeout periods (Table 1). Timeout settings can be hard wired, or they can be controlled with logic gates and modified during operation. To ensure smooth transitions, the system should strobe WDI immediately before the timing settings are changed. This minimizes the risk of initializing a setting change too late in the timer countdown period and generating undesired watchdog outputs. After changing the timing settings, two outcomes are possible based on WDO. If the change is made while WDO is asserted, the previous setting is allowed to finish, the characteristics of the new setting are assumed, and the new startup phase is entered after a 300s setup time (tSETUP) elapses. If the change is made while WDO is not asserted, the new setting is initiated immediately, and the new startup phase is entered after the 300s setup time elapses.
tWD WDI WDO * * * tWD * *
tWD
SET_ tSETUP *IGNORED EDGE tDELAY tWD tSETUP tDELAY tWD
Figure 3. Setting Change Timing _______________________________________________________________________________________ 7
Pin-Selectable Watchdog Timers MAX6369-MAX6374
to register a logic high while supplying all input current and leakage paths connected to the WDO line. A 10k pullup is sufficient in most applications. The MAX6370/ MAX6372/MAX6374 have push-pull outputs that provide an active-low watchdog output pulse of 1ms. When WDO deasserts, timing begins again at the beginning of the watchdog timeout period (Figure 2).
START
SET WDI HIGH PROGRAM CODE
Usage in Noisy Environments
If using the watchdog timer in an electrically noisy environment, a bypass capacitor of 0.1F should be connected between VCC and GND as close to the device as possible, and no further away than 0.2 inches.
SUBROUTINE OR PROGRAM LOOP SET WDI LOW
POSSIBLE INFINITE LOOP PATH
________________Watchdog Software Considerations
To help the watchdog timer monitor software execution more closely, 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 4 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 end 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 be quickly corrected, since the I/O is continually set low and the watchdog timer is allowed to time out, causing WDO to pulse.
RETURN
Figure 4. Watchdog Flow Diagram
Selecting 011 (SET2 = 0, SET1 = 1, SET0 = 1) disables the watchdog timer function on all devices in the family. Operation can be reenabled without powering down by changing the set inputs to the new desired setting. The device assumes the new selected timing characteristics and enter the startup phase after the 300s setup time elapses (Figure 3). The MAX6373/MAX6374 offer a first-edge feature. In first-edge mode (settings 101 or 110, Table 1), the internal timer does not control the startup delay period. Instead, startup terminates when WDI sees a transition. If changing to first-edge mode while the device is operating, disable mode must be entered first. It is then safe to select first-edge mode. Entering disable mode first ensures the output is unasserted when selecting firstedge mode and removes the danger of WDI being masked out.
Pin Configuration
TOP VIEW
WDI 1 GND 2 N.C. 3 8 VCC WDO SET2 SET1
Output
The MAX6369/MAX6371/MAX6373 have an active-low, open-drain output that provides a watchdog output pulse of 100ms. This output structure sinks current when WDO is asserted. Connect a pullup resistor from WDO to any supply voltage up to +5.5V. Select a resistor value large enough to register a logic low (see Electrical Characteristics), and small enough
SET0 4
MAX6369 MAX6370 MAX6371 MAX6372 MAX6373 MAX6374 SOT23-8
7 6 5
Chip Information
TRANSISTOR COUNT: 1500 PROCESS: BiCMOS
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.
8 _____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 (c) 2003 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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