19-1676; Rev 5; 1/11 Pin-Selectable Watchdog Timers The MAX6369–MAX6374 are pin-selectable watchdog timers that supervise microprocessor (µP) 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 µP 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 µP 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. Features o Precision Watchdog Timer for Critical µP 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 8µA Low Supply Current o No External Components Required o Miniature 8-Pin SOT23 Package Ordering Information TEMP RANGE PART PINPACKAGE TOP MARK MAX6369KA-T -40°C to +125°C 8 SOT23 AADC • Watchdog output/timing options: open drain (100ms) or push-pull (1ms). MAX6369KA/V-T -40°C to +125°C 8 SOT23 AEQV MAX6369KA/V+T -40°C to +125°C 8 SOT23 AEQV The MAX6369–MAX6374 operate over a +2.5V to +5.5V supply range and are available in miniature 8-pin SOT23 packages. MAX6370KA-T -40°C to +125°C 8 SOT23 AADD MAX6371KA-T -40°C to +125°C 8 SOT23 AADE MAX6372KA-T -40°C to +125°C 8 SOT23 AADF ________________________Applications MAX6373KA-T -40°C to +125°C 8 SOT23 AADG Industrial Controllers MAX6374KA-T -40°C to +125°C 8 SOT23 AADH Note: All devices are available in tape-and-reel only. Required order increment is 2,500 pieces. Critical µP and Microcontroller (µC) Monitoring /V denotes an automotive qualified part. Automotive Devices are available in both leaded and lead-free packaging. Specify lead-free by replacing “-T” with “+T” when ordering. Embedded Control Systems Telecommunications Pin Configuration appears at end of data sheet. Networking Selector Guide OUTPUT WDO PULSE WIDTH (ms) MAX6369 Open Drain 100 Selectable: 1ms to 60s Selectable: 1ms to 60s MAX6370 Push-Pull 1 Selectable: 1ms to 60s Selectable: 1ms to 60s MAX6371 Open Drain 100 60s Selectable: 1ms to 60s MAX6372 Push-Pull 1 60s Selectable: 1ms to 60s MAX6373 Open Drain 100 Selectable: 200µs to 60s or first edge Selectable: 30µs to 10s MAX6374 Push-Pull 1 Selectable: 200µs to 60s or first edge Selectable: 30µs to 10s PART MINIMUM STARTUP DELAY MINIMUM WATCHDOG TIMEOUT ________________________________________________________________ Maxim Integrated Products For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com. 1 MAX6369–MAX6374 General Description MAX6369–MAX6374 Pin-Selectable Watchdog Timers 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 = +70°C) 8-Pin SOT23 (derate 8.75mW/°C above +70°C).........700mW Operating Temperature Range .........................-40°C to +125°C Storage Temperature Range .............................-65°C to +150°C Junction Temperature ......................................................+150°C VCC Rise or Fall Rate......................................................0.05V/µs Lead Temperature (soldering, 10s) .................................+300°C Soldering Temperature (reflow) Lead(Pb)-free...................................................................+260°C Containing Lead (Pb).......................................................+240°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 = +2.5V to +5.5V, SET_ = VCC or GND, TA = -40°C to +125°C, unless otherwise noted. Typical values are at TA = +25°C and VCC = +3V.) (Note 1) PARAMETER SYMBOL CONDITIONS Operating Voltage Range VCC Supply Current ICC No load VIH WDI, SET0, SET1, SET2 Input High Voltage Input Low Voltage VIL Logic Input Current (Note 2) WDO Output Low Voltage WDO Leakage Current WDO Output High Voltage 2 MIN WDI, SET0, SET1, SET2 ILKG VOH MAX UNITS 5.5 V TA = -40°C to +85°C 8 20 TA = -40°C to +125°C 10 22 µA 0.8 × VCC V VCC ≥ 3.3V, TA = -40°C to +85°C 0.8 VCC ≥ 3.3V, TA = -40°C to +125°C 0.6 VCC ≥ 2.5V, TA = -40°C to +85°C 0.6 VCC ≥ 2.5V, TA = -40°C to +125°C 0.4 V VWDI or VSET_ = 0V or VCC VOL TYP 2.5 ±10 nA ISINK = 1.2mA, VCC > 2.7V, watchdog output asserted 0 0.3 V ISINK = 6mA, VCC > 4.5V, watchdog output asserted 0.4 V 1 µA VWDO = 0 to +5.5V, output deasserted, MAX6369/MAX6371/MAX6373 ISOURCE = 500µA, VCC > 2.7V, watchdog output deasserted 0.8 × VCC ISOURCE = 800µA, VCC > 4.5V, watchdog output deasserted VCC - 1.5 V _______________________________________________________________________________________ Pin-Selectable Watchdog Timers (VCC = +2.5V to +5.5V, SET_ = VCC or GND, TA = -40°C to +125°C, unless otherwise noted. Typical values are at TA = +25°C and VCC = +3V.) (Note 1) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS MAX6369/MAX6370 Startup Delay Period Watchdog Timeout Period tDELAY tWD VSET2 = 0V, VSET1 = 0V, VSET0 = 0V 1 3 VSET2 = 0V, VSET1 = 0,V SET0 = VCC 10 30 VSET2 = 0V, SET1 = VCC, VSET0 = 0V 30 90 VSET2 = 0V, SET1 = VCC, SET0 = VCC Watchdog Disabled SET2 = VCC, VSET1 = 0V, VSET0 = 0V 100 300 SET2 = VCC, VSET1 = 0V, SET0 = VCC 1 3 SET2 = VCC, SET1 = VCC, VSET0 = 0V 10 30 SET2 = VCC, SET1 = VCC, SET0 = VCC 60 180 VSET2 = 0V, VSET1 = 0V, VSET0 = 0V 1 3 VSET2 = 0V, VSET1 = 0V, SET0 = VCC 10 30 VSET2 = 0V, SET1 = VCC, VSET0 = 0V 30 90 VSET2 = 0V, SET1 = VCC, SET0 = VCC SET2 = VCC, VSET1 = 0V, VSET0 = 0V ms ms s ms Watchdog Disabled 100 300 SET2 = VCC, VSET1 = 0V, SET0 = VCC 1 3 SET2 = VCC, SET1 = VCC, VSET0 = 0V 10 30 SET2 = VCC, SET1 = VCC, SET0 = VCC 60 180 ms s MAX6371/MAX6372 Startup Delay Period Watchdog Time-Out Period tDELAY tWD VSET2 = 0V, SET1 = VCC, SET0 = VCC All other SET_ conditions Watchdog Disabled 60 180 VSET2 = 0V, VSET1 = 0V, VSET0 = 0V 1 3 VSET2 = 0V, VSET1 = 0V, SET0 = VCC 3 9 VSET2 = 0V, SET1 = VCC, VSET0 = 0V 10 30 VSET2 = 0V, SET1 = VCC, SET0 = VCC s ms Watchdog Disabled SET2 = VCC, VSET1 = 0V, VSET0 = 0V 100 300 SET2 = VCC, VSET1 = 0V, SET0 = VCC 300 900 SET2 = VCC, SET1 = VCC, VSET0 = 0V 3 9 SET2 = VCC, SET1 = VCC, SET0 = VCC 60 180 ms s MAX6373/MAX6374 Startup Delay Period tDELAY VSET2 = 0V, VSET1 = 0V, VSET0 = 0V 3 9 VSET2 = 0V, VSET1 = 0V, SET0 = VCC 3 9 VSET2 = 0V, SET1 = VCC, VSET0 = 0V 60 180 SET2 = 0V, SET1 = VCC, SET0 = VCC SET2 = VCC, VSET1 = 0V, VSET0 = 0V s Watchdog Disabled 200 600 SET2 = VCC, VSET1 = 0V, SET0 = VCC First Edge (Note 3) SET2 = VCC, SET1 = VCC, VSET0 = 0V First Edge (Note 3) SET2 = VCC, SET1 = VCC, SET0 = VCC ms 60 180 µs s _______________________________________________________________________________________ 3 MAX6369–MAX6374 ELECTRICAL CHARACTERISTICS (continued) ELECTRICAL CHARACTERISTICS (continued) (VCC = +2.5V to +5.5V, SET_ = VCC or GND, TA = -40°C to +125°C, unless otherwise noted. Typical values are at TA = +25°C and VCC = +3V.) (Note 1) PARAMETER SYMBOL Watchdog Timeout Period tWD Watchdog Input Pulse Width (Note 2) tWDI Watchdog Output Pulse Width tWDO Internal Setup Time (Note 4) tSETUP CONDITIONS MIN TYP MAX UNITS ms VSET2 = 0V, VSET1 = 0V, VSET0 = 0V 3 9 VSET2 = 0V, VSET1 = 0V, SET0 = VCC 3 9 VSET2 = 0V, SET1 = VCC, VSET0 = 0V 1 3 VSET2 = 0V, SET1 = VCC, SET0 = VCC s Watchdog Disabled SET2 = VCC, VSET1 = 0V, VSET0 = 0V 30 90 SET2 = VCC, VSET1 = 0V, SET0 = VCC 1 3 µs s SET2 = VCC, SET1 = VCC, VSET0 = 0V 10 30 SET2 = VCC, SET1 = VCC, SET0 = VCC 10 30 After WDO deasserted 100 MAX6369/MAX6371/MAX6373 100 300 ms MAX6370/MAX6372/MAX6374 1 3 ms 100 300 ms After WDO deasserted ns Note 1: Production tested at TA = +25°C. 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 the Selecting Device Timing section 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 = +25°C, unless otherwise noted.) SUPPLY CURRENT vs. TEMPERATURE WATCHDOG TIMEOUT PERIOD vs. TEMPERATURE VCC = +5.5V 10 8 VCC = +2.5V 6 4 1.002 1.001 1.000 0.999 0.998 0.997 -40 -15 10 35 TEMPERATURE (°C) 4 MAX6369/74-02 12 1.003 NORMALIZED WATCHDOG TIMEOUT PERIOD MAX6369/74-01 14 SUPPLY CURRENT (μA) MAX6369–MAX6374 Pin-Selectable Watchdog Timers 60 85 -40 -15 10 35 TEMPERATURE (°C) _______________________________________________________________________________________ 60 85 Pin-Selectable Watchdog Timers PIN NAME FUNCTION 1 WDI 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. 2 GND Ground 3 N.C. Not Connected. Do not make any connection to this pin. 4 SET0 Set Zero. Logic input for selecting startup delay and watchdog timeout periods. See Table 1 for timing details. 5 SET1 Set One. Logic input for selecting startup delay and watchdog timeout periods. See Table 1 for timing details. 6 SET2 Set Two. Logic input for selecting startup delay and watchdog timeout periods. See Table 1 for timing details. 7 WDO 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. 8 VCC Supply Voltage (+2.5V to +5.5V) Table 1. Minimum Timeout Settings LOGIC INPUTS MAX6369/MAX6370 MAX6371/MAX6372 MAX6373/MAX6374 SET2 SET1 SET0 tDELAY, tWD tDELAY = 60s, tWD tDELAY tWD 0 0 0 1ms 1ms 3ms 3ms 0 0 1 10ms 3ms 3s 3s 0 1 0 30ms 10ms 60s 1s 0 1 1 Disabled Disabled Disabled Disabled 1 0 0 100ms 100ms 200μs 30μs 1 0 1 1s 300ms First Edge 1s 1 1 0 10s 3s First Edge 10s 1 1 1 60s 60s 60s 10s Detailed Description The MAX6369–MAX6374 are flexible watchdog circuits for monitoring µP activity. During normal operation, the internal timer is cleared each time the µP 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 µP system to power up and initialize before assuming responsibility for normal watchdog timer updates. Includes several fixed or pin-selectable startup delay options from 200µs to 60s, and an option to wait for the first watchdog input transition before starting the watchdog timer. _______________________________________________________________________________________ 5 MAX6369–MAX6374 Pin Description MAX6369–MAX6374 Pin-Selectable Watchdog Timers WDI VCC MAX6369–MAX6374 TRANSITION DETECTOR SET 2 CLEAR CONTROL LOGIC SET 1 EN ENABLE SET 0 SET WATCHDOG TIMEOUT OUT WDO OUTPUT SET STARTUP DELAY WATCHDOG TIMER CIRCUITRY GND Figure 1. Functional Diagram VCC tSETUP tDELAY tWD tWD tWD WDI A A B C E F D G E tWDO 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. 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 30µs to 60s. Pin-selectable watchdog timer disable feature. 6 • 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 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). 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 300µs 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 300µs 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 300µs setup time elapses. 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 200µs to 60s minimum, and watchdog timeout tWD WDI * * WDO * * * tWD tWD SET_ tSETUP tDELAY tWD tSETUP tDELAY tWD *IGNORED EDGE Figure 3. Setting Change Timing _______________________________________________________________________________________ 7 MAX6369–MAX6374 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 µP 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. Pin-Selectable Watchdog Timers MAX6369–MAX6374 Output START SET WDI HIGH PROGRAM CODE SUBROUTINE OR PROGRAM LOOP POSSIBLE INFINITE LOOP PATH SET WDI LOW 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 to register a logic high while supplying all input current and leakage paths connected to the WDO line. A 10kΩ 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). Usage in Noisy Environments 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 300µs setup time elapses (Figure 3). WDO is high when the watchdog timer is disabled. 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. 8 If using the watchdog timer in an electrically noisy environment, a bypass capacitor of 0.1µF should be connected between VCC and GND as close to the device as possible, and no further away than 0.2 inches. ________________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. _______________________________________________________________________________________ Pin-Selectable Watchdog Timers Chip Information TRANSISTOR COUNT: 1500 PROCESS: BiCMOS TOP VIEW WDI 1 GND 2 N.C. 3 SET0 4 MAX6369 MAX6370 MAX6371 MAX6372 MAX6373 MAX6374 SOT23 8 VCC 7 WDO 6 SET2 5 SET1 Package Information For the latest package outline information and land patterns, go to www.maxim-ic.com/packages. Note that a “+”, “#”, or “-” in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing pertains to the package regardless of RoHS status. PACKAGE TYPE PACKAGE CODE OUTLINE NO. LAND PATTERN NO. 8 SOT23 K8SN-1 21-0078 90-0176 _______________________________________________________________________________________ 9 MAX6369–MAX6374 Pin Configuration MAX6369–MAX6374 Pin-Selectable Watchdog Timers Revision History REVISION NUMBER REVISION DATE 0 1 4/00 7/00 DESCRIPTION PAGES CHANGED Initial release Removed future product asterisk for MAX6370. — 1 2 2/03 Corrected limits in Electrical Characteristics. 4 3 12/05 Added lead-free information to Ordering Information. 1 4 6/10 Revised the Ordering Information, Absolute Maximum Ratings, Electrical Characteristics, and the Selecting Device Timing section. 5 1/11 Updated the top mark information in the Ordering Information section. 1, 2, 8 1 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 © 2011 Maxim Integrated Products Maxim is a registered trademark of Maxim Integrated Products, Inc.