MAX6370KA-T资料

Pin-Selectable Watchdog Timers

General Description

Features

The MAX6369–MAX6374 are pin-selectable watchdogtimers that supervise microprocessor (µP) activity and♦Precision Watchdog Timer for Critical signal when a system is operating improperly. DuringµP Applicationsnormal operation, the microprocessor should repeated-♦Pin-Selectable Watchdog Timeout Periodsly toggle the watchdog input (WDI) before the selectedwatchdog timeout period elapses to demonstrate that♦Pin-Selectable Watchdog Startup Delay Periodsthe system is processing code properly. If the µP does♦Ability to Change Watchdog Timing Characteristicsnot provide a valid watchdog input transition before theWithout Power Cyclingtimeout period expires, the supervisor asserts a watch-dog (WDO) output to signal that the system is not exe-♦Open-Drain or Push-Pull Pulsed Active-Low cuting the desired instructions within the expected timeWatchdog Outputframe. The watchdog output pulse can be used to resetthe µP or interrupt the system to warn of processing♦Watchdog Timer Disable Featureerrors.

♦+2.5V to +5.5V Operating Voltage The MAX6369–MAX6374 are flexible watchdog timer♦8µA Low Supply Current

supervisors that can increase system reliability throughnotification of code execution errors. The family offers♦No External Components Requiredseveral pin-selectable watchdog timing options to♦Miniature 8-Pin SOT23 Package

match a wide range of system timing applications:

•Watchdog startup delay: provides an initial delaybefore the watchdog timer is started.

Ordering Information•Watchdog timeout period: normal operating watch-TEMPPIN-TOPdog timeout period after the initial startup delay.

PARTRANGEPACKAGEMARKS•Watchdog output/timing options: open drain (100ms)MAX6369KA-T-40°C to +85°C8 SOT23-8AADCor push-pull (1ms).

MAX6370KA-T-40°C to +85°C8 SOT23-8AADDThe MAX6369–MAX6374 operate over a +2.5V to +5.5VMAX6371KA-T-40°C to +85°C8 SOT23-8AADEsupply range and are available in miniature 8-pinSOT23 packages.

MAX6372KA-T-40°C to +85°C8 SOT23-8AADF________________________Applications

MAX6373KA-T-40°C to +85°C8 SOT23-8AADGMAX6374KA-T-40°C to +85°C8 SOT23-8AADHEmbedded Control SystemsNote:All devices are available in tape-and-reel only. RequiredIndustrial Controllers

order increment is 2,500 pieces.

Devices are available in both leaded and lead-free packaging.Critical µP and Microcontroller (µC) MonitoringSpecify lead-free by replacing “-T” with “+T” when ordering.

Automotive

TelecommunicationsPin Configuration appears at end of data sheet.

Networking

Selector Guide

PARTOUTPUTWDO PULSEWIDTH (ms)MINIMUM STARTUP DELAYMINIMUM WATCHDOG TIMEOUTMAX6369Open Drain100Selectable: 1ms to 60sS el ectab le : 1ms to 60sMAX6370Push-Pull1Selectable: 1ms to 60sS el ectab le : 1ms to 60sMAX6371Open Drain10060sS el ectab le : 1ms to 60sMAX6372Push-Pull160sS el ectab le : 1ms to 60sMAX6373Open Drain100S el ectab le : 200µs to 60s or fi r st ed ge S el ectab le : 30µs to 10sMAX6374Push-Pull1S el ectab le : 200µs to 60s or fi r st ed ge S el ectab le : 30µs to 10s________________________________________________________________Maxim Integrated Products1For pricing, delivery, and ordering information,please contact Maxim/Dallas Direct!at

1-888-629-42, or visit Maxim’s website at www.maxim-ic.com.

MAX6369–MAX6374元器件交易网www.cecb2b.comPin-Selectable Watchdog TimersMAX6369–MAX6374ABSOLUTE MAXIMUM RATINGS

Terminal Voltage (with respect to GND)

VCC.....................................................................-0.3V to +6VWDI.....................................................................-0.3V to +6VWDO(Open Drain: MAX6369/71/73).................-0.3V to +6VWDO(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)

SOT23-8 (derate 8.75mW/°C above +70°C)...............700mWOperating Temperature Range...........................-40°C to +85°C Storage Temperature Range.............................-65°C to +150°CJunction Temperature......................................................+150°CLead Temperature (soldering, 10s).................................+300°CVCCRise or Fall Rate......................................................0.05V/µs

Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functionaloperation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure toabsolute maximum rating conditions for extended periods may affect device reliability.

ELECTRICAL CHARACTERISTICS

(VCC= +2.5V to +5.5V, SET_ = VCCor GND, TA= -40°C to +85°C, unless otherwise noted. Typical values are at TA= +25°C and VCC= +3V.) (Note 1)PARAMETEROperating Voltage RangeSupply CurrentInput High VoltageInput Low VoltageLogic Input Current (Note 2)WDO Output LowVoltageSYMBOLVCCICCVIHVILNo loadWDI, SET0, SET1, SET2WDI, SET0, SET1,SET2WDI or SET_ = 0 or VCCISINK = 1.2mA, VCC > 2.7V, watchdogoutput assertedISINK = 6mA, VCC > 4.5V, watchdogoutput assertedV NDO = 0 to +5.5V, output deasserted,MAX6369/MAX6371/MAX6373ISOURCE = 500µA, VCC > 2.7V, watchdogoutput deassertedISOURCE = 800µA, VCC > 4.5V, watchdogoutput deassertedSET2 = 0, SET1 = 0, SET0 = 0SET2 = 0, SET1 = 0, SET0 = VCCSET2 = 0, SET1 = VCC, SET0 = 0SET2 = 0, SET1 = VCC, SET0 = VCCStartup Delay PeriodtDELAYSET2 = VCC, SET1 = 0, SET0 = 0SET2 = VCC, SET1 = 0, SET0 = VCCSET2 = VCC, SET1 = VCC, SET0 = 0SET2 = VCC, SET1 = VCC, SET0 = VCC0.8 × VCCVVCC - 1.5VCC ≥ 3.3VVCC ≥ 2.5V00.8 × VCC0.80.6±100.30.41CONDITIONSMIN2.58TYPMAX5.520UNITSVµAVVnAVVµAVOLWDO Leakage CurrentILKGWDO Output HighVoltage MAX6369/MAX6370VOH110301001106033090300330180 smsmsWatchdog Disabled2_______________________________________________________________________________________

元器件交易网www.cecb2b.comPin-Selectable Watchdog Timers

ELECTRICAL CHARACTERISTICS (continued)

(VCC= +2.5V to +5.5V, SET_ = VCCor GND, TA= -40°C to +85°C, unless otherwise noted. Typical values are at TA= +25°C and VCC= +3V.) (Note 1)PARAMETERSYMBOLCONDITIONSSET2 = 0, SET1 = 0, SET0 = 0SET2 = 0, SET1 = 0, SET0 = VCCSET2 = 0, SET1 = VCC, SET0 = 0Watchdog TimeoutPeriodtWDSET2 = 0, SET1 = VCC, SET0 = VCCSET2 = VCC, SET1 = 0, SET0 = 0SET2 = VCC, SET1 = 0, SET0 = VCCSET2 = VCC, SET1 = VCC, SET0 = 0SET2 = VCC, SET1 = VCC, SET0 = VCCMAX6371/MAX6372Startup Delay PeriodtDELAYSET2 = 0, SET1 = VCC, SET0 = VCCAll other SET_ conditionsSET2 = 0, SET1 = 0, SET0 = 0Watchdog Disabled6011803sMIN1103010011060TYPMAX33090300330180smsmsUNITSMAX6369–MAX6374Watchdog DisabledSET2 = 0, SET1 = 0, SET0 = VCC39msSET2 = 0, SET1 = VCC, SET0 = 01030Watchdog Time-OutSET2 = 0, SET1 = VCC, SET0 = VCCWatchdog DisabledPeriodtWDSET2 = VCC, SET1 = 0, SET0 = 0100300SET2 = VCC, SET1 = 0, SET0 = VCC300900msSET2 = VCC, SET1 = VCC, SET0 = 039SET2 = VCC, SET1 = VCC, SET0 = VCC60180sMAX6373/MAX6374SET2 = 0, SET1 = 0, SET0 = 039msSET2 = 0, SET1 = 0, SET0 = VCC39SET2 = 0, SET1 = VCC, SET0 = 060180sStartup Delay PeriodtSET2 = 0, SET1 = VWatchdog DisabledDELAYCC, SET0 = VCCSET2 = VCC, SET1 = 0, SET0 = 0200600µsSET2 = VCC, SET1 = 0, SET0 = VCCFirst Edge (Note 3)SET2 = VCC, SET1 = VCC, SET0 = 0First Edge (Note 3)SET2 = VCC, SET1 = VCC, SET0 = VCC60180sSET2 = 0, SET1 = 0, SET0 = 039msSET2 = 0, SET1 = 0, SET0 = VCC39SET2 = 0, SET1 = VCC, SET0 = 013sWatchdog TimeoutCC, SET0 = VCCWatchdog DisabledPeriodtWDSET2 = 0, SET1 = VSET2 = VCC, SET1 = 0, SET0 = 03090µsSET2 = VCC, SET1 = 0, SET0 = VCC13SET2 = VCC, SET1 = VCC, SET0 = 01030sSET2 = VCC, SET1 = VCC, SET0 = VCC1030_______________________________________________________________________________________3

元器件交易网www.cecb2b.comPin-Selectable Watchdog TimersMAX6369–MAX6374ELECTRICAL CHARACTERISTICS (continued)

(VCC= +2.5V to +5.5V, SET_ = VCCor GND, TA= -40°C to +85°C, unless otherwise noted. Typical values are at TA= +25°C and VCC= +3V.) (Note 1)PARAMETERWatchd og Inp ut P ul se Wi dt h( No te 2) Watchdog Output Pulse WidthInternal Setup Time(Note 4)SYMBOLtWDItWDOtSETUPCONDITIONSAfter WDO deassertedMAX6369/MAX6371/MAX6373MAX6370/MAX6372/MAX6374After WDO deassertedMIN10010011003003300TYPMAXUNITSnsmsmsµsNote 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 Selecting

Device Timingfor 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 CURRENTvs. TEMPERATURE

MAX6369/74-01WATCHDOG TIMEOUT PERIOD

vs. TEMPERATURE

NORMALIZED WATCHDOG TIMEOUT PERIODMAX6369/74-02141.0031.0021.0011.0000.9990.9980.997

12SUPPLY CURRENT (µA)VCC = +5.5V10

8

VCC = +2.5V6

4-40

-15

10

35

60

85

TEMPERATURE (°C)

-40-1510356085

TEMPERATURE (°C)

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元器件交易网www.cecb2b.comPin-Selectable Watchdog Timers

Pin Description

PINNAMEFUNCTIONWatchdog Input. If WDI remains either high or low for the duration of the watchdog timeout period (tWD), WDO1WDItriggers a pulse. The internal watchdog timer clears whenever a WDO is asserted or whenever WDI sees arising or falling edge.2GNDGround3N.C.Not Connected. Do not make any connection to this pin.4SET0S et Z er o. Log ic i np ut for sel ecti ng star tup d el ay and w atchd og ti me out p er i od s. S ee Tab le 1 for ti m in g d etai ls .5SET1S et One. Log ic i np ut for sel ecti ng star tup d el ay and w atchd og ti me out p er io d s. S ee Tab l e 1 for ti mi ng d etai ls .6SET2S et Tw o. Log ic i np ut for sel ecti ng star tup d el ay and w atchd og ti me out p er io d s. S ee Tab l e 1 for ti mi n g d etai ls .Watchdog Output. Pulses low for the watchdog output pulse width, tWDO, when the internal watchdog times7WDOout. The MAX6369/MAX6371/MAX6373 have open-drain outputs and require a pull-up resistor. TheMAX6370/MAX6372/MAX6374 outputs are push-pull.8VCCSupply Voltage (+2.5V to +5.5V)Table 1. Minimum Timeout SettingsLOGIC INPUTSMAX6369/MAX6370MAX6371/MAX6372MAX6373/MAX6374SET2SET1SET0tDELAY, tWDtDELAY = 60s, tWDtDELAYtWD0001ms1ms3ms3ms00110ms3ms3s3s01030ms10ms60s1s011DisabledDisabledDisabledDisabled100100ms100ms200µs30µs1011s300msFirst Edge1s11010s3sFirst Edge10s11160s60s60s10sDetailed Descriptionwatchdog timeout period are summarized below (seeThe MAX6369–MAX6374 are flexible watchdog circuitsTable 1 for the timeout characteristics for all devices infor monitoring µP activity. During normal operation, thethe family):

internal timer is cleared each time the µP toggles the•Watchdog Startup Delay:

WDI with a valid logic transition (low to high or high tolow) within the selected timeout period (tProvides an initial delay before the watchdog timer isremains high as long as the input is strobed within theWD). The WDOstarted.

selected timeout period. If the input is not strobedAllows time for the µP system to power up and initial-before the timeout period expires, the watchdog outputize before assuming responsibility for normal watch-is asserted low for the watchdog output pulse widthdog timer updates.

(tWDO). The device type and the state of the three logicIncludes several fixed or pin-selectable startup delaycontrol pins (SET0, SET1, and SET2) determine watch-options from 200µs to 60s, and an option to wait fordog timing characteristics. The three basic timing varia-the first watchdog input transition before starting thetions for the watchdog startup delay and the normal

watchdog timer.

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MAX6369–MAX6374元器件交易网www.cecb2b.comPin-Selectable Watchdog TimersMAX6369–MAX6374VCCWDIMAX6369–MAX6374TRANSITIONDETECTORENSET 2SET 1SET 0CONTROLLOGICCLEARENABLESET WATCHDOG TIMEOUTSET STARTUP DELAYWATCHDOGTIMER CIRCUITRYGNDOUTOUTPUTWDOFigure 1. Functional Diagram

VCCtSETUPtDELAYtWDtWDtWDWDIAWDOA TRANSITIONS ON WDI IGNORED DURING SETUP DELAY.BTRANSITION(S) ON WDI IGNORED DURING STARTUP DELAY PERIOD.CWATCHDOG TIMER STARTS AFTER STARTUP DELAY AND WDO IS DEASSERTED.DTRANSITION OCCURS BEFORE WATCHDOG TIMEOUT PERIOD. WATCHDOG TIMER CLEARS AND STARTS TIMER AGAIN.EWATCHDOG TIMES OUT, WDO ASSERTS.FTRANSITIONS ON WDI IGNORED WHEN WDO ASSERTED.GWATCHDOG TIMER STARTS AFTER WDO DEASSERTS.ABCDEFtWDOGEFigure 2. Watchdog Timing•Watchdog Timeout Period:

Normal operating watchdog timeout period after theinitial startup delay.

A watchdog output pulse is asserted if a valid watch-dog input transition is not received before the timeoutperiod elapses.

Eight pin-selectable timeout period options for eachdevice, from 30µs to 60s.

Pin-selectable watchdog timer disable feature.

6

•Watchdog Output/Timing Options:

Open drain, active low with 100ms minimum watch-dog output pulse (MAX6369/MAX6371/MAX6373).Push-pull, active low with 1ms minimum watchdogoutput pulse (MAX6370/MAX6372/MAX6374).

Each device has a watchdog startup delay that is initi-ated when the supervisor is first powered or after theuser modifies any of the logic control set inputs. Thewatchdog timer does not begin to count down until the

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元器件交易网www.cecb2b.comPin-Selectable Watchdog Timers

completion of the startup delay period, and no watch-delays from 3ms to 10s minimum. Two of the selectabledog output pulses are asserted during the startupmodes do not initiate the watchdog timer until thedelay. When the startup delay expires, the watchdogdevice receives its first valid watchdog input transitionbegins counting its normal watchdog timeout period(there is no fixed period by which the first input must beand waiting for WDI transitions. The startup delayreceived). These two extended startup delay modesallows time for the µP system to power up and fully ini-are useful for applications requiring more than 60s fortialize before assuming responsibility for the normalsystem initialization.

watchdog timer updates. Startup delay periods varybetween the different devices and may be altered byAll the MAX6369–MAX6374 devices may be disabledthe logic control set pins. To ensure that the systemwith the proper logic control pin setting (Table 1).

generates no undesired watchdog outputs, the routineApplications Informationwatchdog input transitions should begin before theselected minimum startup delay period has expired.Input Signal Considerations

The normal watchdog timeout period countdown is initi-Watchdog timing is measured from the last WDI risingated when the startup delay is complete. If a valid logicor falling edge associated with a pulse of at least 100nstransition is not recognized at WDI before the watchdogin width. WDI transitions are ignored when WDOistimeout period has expired, the supervisor asserts aasserted, and during the startup delay period (Figurewatchdog output. Watchdog timeout periods vary2). Watchdog input transitions are also ignored for abetween the different devices and may be altered bysetup period, tSETUP, of up to 300µs after power-up orthe logic control set pins. To ensure that the systema setting change (Figure 3).

generates no undesired watchdog outputs, the watch-Selecting Device Timing

dog input transitions should occur before the selectedminimum watchdog timeout period has expired.SET2, SET1, and SET0 program the startup delay andwatchdog timeout periods (Table 1). Timeout settingsThe startup delay and the watchdog timeout period arecan be hard wired, or they can be controlled with logicdetermined by the states of the SET0, SET1, and SET2gates and modified during operation. To ensure smoothpins, and by the particular device within the family. Fortransitions, the system should strobe WDI immediatelythe MAX6369 and MAX6370, the startup delay is equalbefore the timing settings are changed. This minimizesto the watchdog timeout period. The startup andthe risk of initializing a setting change too late in thewatchdog timeout periods are pin selectable from 1mstimer countdown period and generating undesiredto 60s (minimum).

watchdog outputs. After changing the timing settings,For the MAX6371 and MAX6372, the startup delay istwo outcomes are possible based on WDO. If thefixed at 60s and the watchdog timeout period is pinchange is made while WDOis asserted, the previousselectable from 1ms to 60s (minimum).

setting is allowed to finish, the characteristics of theThe MAX6373/MAX6374 provide two timing variationsnew setting are assumed, and the new startup phase isfor the startup delay and normal watchdog timeout.entered after a 300µs setup time (tFive of the pin-selectable modes provide startup delaysthe change is made while WDOis not asserted, theSETUP) elapses. Iffrom 200µs to 60s minimum, and watchdog timeout

new setting is initiated immediately, and the new start-up phase is entered after the 300µs setup time elapses.

tWDWDI*****WDOtWDtWDSET_tSETUPtDELAYtWDtSETUPtDELAYtWD*IGNORED EDGEFigure 3. Setting Change Timing

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MAX6369–MAX6374元器件交易网www.cecb2b.comPin-Selectable Watchdog TimersMAX6369–MAX6374to register a logic high while supplying all input currentand leakage paths connected to the WDOline. A 10kΩpullup is sufficient in most applications. The MAX6370/MAX6372/MAX6374 have push-pull outputs that pro-vide an active-low watchdog output pulse of 1ms.When WDOdeasserts, timing begins again at thebeginning of the watchdog timeout period (Figure 2).

STARTSET WDIHIGHPROGRAMCODEUsage in Noisy Environments

If using the watchdog timer in an electrically noisy envi-ronment, a bypass capacitor of 0.1µF should be con-nected between VCCand GND as close to the deviceas possible, and no further away than 0.2 inches.

SUBROUTINE ORPROGRAM LOOPSET WDI LOWPOSSIBLE INFINITE LOOP PATH________________Watchdog Software

Considerations

To help the watchdog timer monitor software executionmore closely, set and reset the watchdog input at differ-ent points in the program, rather than pulsing the watch-dog input high-low-high or low-high-low. This techniqueavoids a stuck loop, in which the watchdog timer wouldcontinue to be reset inside the loop, keeping the watch-dog from timing out. Figure 4 shows an example of aflow diagram where the I/O driving the watchdog input isset high at the beginning of the program, set low at theend of every subroutine or loop, then set high againwhen the program returns to the beginning. If the pro-gram should hang in any subroutine, the problem wouldbe quickly corrected, since the I/O is continually set lowand the watchdog timer is allowed to time out, causingWDOto pulse.

RETURNFigure 4. Watchdog Flow Diagram

Selecting 011 (SET2 = 0, SET1 = 1, SET0 = 1) disablesthe watchdog timer function on all devices in the family.Operation can be reenabled without powering down bychanging the set inputs to the new desired setting. Thedevice assumes the new selected timing characteris-tics and enter the startup phase after the 300µs setuptime elapses (Figure 3).

The MAX6373/MAX6374 offer a first-edge feature. Infirst-edge mode (settings 101 or 110, Table 1), theinternal 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 oper-ating, disable mode must be entered first. It is then safeto select first-edge mode. Entering disable mode firstensures the output is unasserted when selecting first-edge mode and removes the danger of WDI beingmasked out.

Pin Configuration

TOP VIEWWDI1GND2N.C.38VCCWDOSET2SET1Output

The MAX6369/MAX6371/MAX6373 have an active-low,open-drain output that provides a watchdog outputpulse of 100ms. This output structure sinks currentwhen WDOis asserted. Connect a pullup resistor fromWDOto any supply voltage up to +5.5V.

Select a resistor value large enough to register a logiclow (see Electrical Characteristics), and small enough

SET04MAX6369MAX6370MAX6371MAX6372MAX6373MAX6374SOT23-8765Chip Information

TRANSISTOR COUNT: 1500PROCESS: BiCMOS

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