MAX6369KA+T ,Pin-Selectable Watchdog TimersGeneral Description Beneits and
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MAX636ACSA ,Preset -12V output or adjuistable output with 2 resistors, CMOS switching regulator. Output accuracy 5%.19-0918; Re v tk 5/91
[VI llXI/VI
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MAX6369KA-MAX6369KA/V+T-MAX6369KA+T-MAX6370KA+T-MAX6371KA+-MAX6371KA+T-MAX6373KA+T-MAX6374KA+
Pin-Selectable Watchdog Timers
General DescriptionThe 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.●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.
Beneits and Features●Precision Watchdog Timer for Critical μP Applications●Pin-Selectable Watchdog Timeout Periods●Pin-Selectable Watchdog Startup Delay Periods●Ability to Change Watchdog Timing Characteristics Without Power Cycling●Open-Drain or Push-Pull Pulsed Active-Low Watchdog Output●Watchdog Timer Disable Feature●+2.5V to +5.5V Operating Voltage●8μA Low Supply Current●No External Components Required●Miniature 8-Pin SOT23 Package
Applications●Embedded Control Systems●Industrial Controllers●Critical μP and Microcontroller (μC) Monitoring●Automotive●Telecommunications●Networking
WATCHDOG
TIMER CIRCUITRY
TRANSITION
DETECTOR
ENABLE
SET WATCHDOG TIMEOUT
SET STARTUP DELAY
MAX6369–MAX6374CONTROL
LOGIC
SET 2
SET 1
SET 0
VCC
GND
CLEAR
WDOOUT
WDI
OUTPUT
Functional Diagram
MAX6369–MAX6374Pin-Selectable Watchdog Timers
Terminal Voltage (with respect to GND) VCC ......................................................................-0.3V to +6V WDI ......................................................................-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) 8-Pin SOT23 (derate 8.75mW/°C above +70°C) ........700mWOperating Temperature Range .........................-40°C to +125°CStorage Temperature Range ............................-65°C to +150°C
Junction Temperature ......................................................+150°CVCC Rise or Fall Rate ...................................................0.05V/μsLead Temperature (soldering, 10s) .................................+300°CSoldering Temperature (reflow)Lead(Pb)-free ..................................................................+260°CContaining Lead (Pb) ......................................................+240°C
(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)
Absolute Maximum RatingsStresses 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
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITSOperating Voltage RangeVCC2.55.5V
Supply CurrentICCNo load
TA = -40°C to +85°C820
TA = -40°C to +125°C1022
Input High VoltageVIHWDI, SET0, SET1, SET20.8 x VCCV
Input Low VoltageVILWDI, SET0, SET1, SET2
VCC ≥ 3.3V,
TA = -40°C to +85NC0.8
VCC ≥ 3.3V,
TA = -40°C to +125°C0.6
VCC ≥ 2.5V,
TA = -40°C to +85°C0.6
VCC ≥ 2.5V,
TA = -40°C to +125°C0.4
Logic Input Current (Note 2)VWDI or VSET_ = 0V or VCC0±10nA
WDO Output LowVoltageVOL
ISINK = 1.2mA, VCC > 2.7V, watchdog
output asserted0.3V
ISINK = 6mA, VCC > 4.5V, watchdog output
asserted0.4V
WDO Leakage CurrentILKGVWDO = 0 to +5.5V, output deasserted, MAX6369/MAX6371/MAX63731µA
WDO Output HighVoltageVOH
ISOURCE = 500µA, VCC > 2.7V,
watchdog output deasserted 0.8 x VCCISOURCE = 800µA, VCC > 4.5V,
watchdog output deasserted VCC - 1.5
MAX6369–MAX6374Pin-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)
Electrical Characteristics (continued)
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITS
MAX6369/MAX6370Startup Delay PeriodtDELAY
VSET2 = 0V, VSET1 = 0V, VSET0 = 0V13VSET2 = 0V, VSET1 = 0,V SET0 = VCC1030
VSET2 = 0V, SET1 = VCC, VSET0 = 0V3090
VSET2 = 0V, SET1 = VCC, SET0 = VCCWatchdog Disabled
SET2 = VCC, VSET1 = 0V, VSET0 = 0V100300ms
SET2 = VCC, VSET1 = 0V, SET0 = VCC13SET2 = VCC, SET1 = VCC, VSET0 = 0V1030
SET2 = VCC, SET1 = VCC, SET0 = VCC60180
Watchdog TimeoutPeriodtWD
VSET2 = 0V, VSET1 = 0V, VSET0 = 0V13VSET2 = 0V, VSET1 = 0V, SET0 = VCC1030
VSET2 = 0V, SET1 = VCC, VSET0 = 0V3090
VSET2 = 0V, SET1 = VCC, SET0 = VCCWatchdog Disabled
SET2 = VCC, VSET1 = 0V, VSET0 = 0V100300ms
SET2 = VCC, VSET1 = 0V, SET0 = VCC13SET2 = VCC, SET1 = VCC, VSET0 = 0V1030
SET2 = VCC, SET1 = VCC, SET0 = VCC60180
MAX6371/MAX6372Startup Delay Period tDELAYVSET2 = 0V, SET1 = VCC, SET0 = VCCWatchdog Disabled
All other SET_ conditions60180s
Watchdog Time-OutPeriodtWD
VSET2 = 0V, VSET1 = 0V, VSET0 = 0V13VSET2 = 0V, VSET1 = 0V, SET0 = VCC39
VSET2 = 0V, SET1 = VCC, VSET0 = 0V1030
VSET2 = 0V, SET1 = VCC, SET0 = VCCWatchdog Disabled
SET2 = VCC, VSET1 = 0V, VSET0 = 0V100300msSET2 = VCC, VSET1 = 0V, SET0 = VCC300900
SET2 = VCC, SET1 = VCC, VSET0 = 0V39sSET2 = VCC, SET1 = VCC, SET0 = VCC60180
MAX6373/MAX6374Startup Delay PeriodtDELAY
VSET2 = 0V, VSET1 = 0V, VSET0 = 0V39ms
VSET2 = 0V, VSET1 = 0V, SET0 = VCC39sVSET2 = 0V, SET1 = VCC, VSET0 = 0V60180
SET2 = 0V, SET1 = VCC, SET0 = VCCWatchdog Disabled
SET2 = VCC, VSET1 = 0V, VSET0 = 0V200600µs
SET2 = VCC, VSET1 = 0V, SET0 = VCCFirst Edge (Note 3)
SET2 = VCC, SET1 = VCC, VSET0 = 0VFirst Edge (Note 3)
MAX6369–MAX6374Pin-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)
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.
(Circuit of Functional Diagram, TA = +25°C, unless otherwise noted.)
Electrical Characteristics (continued)
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITSWatchdog TimeoutPeriodtWD
VSET2 = 0V, VSET1 = 0V, VSET0 = 0V39ms
VSET2 = 0V, VSET1 = 0V, SET0 = VCC39sVSET2 = 0V, SET1 = VCC, VSET0 = 0V13
VSET2 = 0V, SET1 = VCC, SET0 = VCCWatchdog Disabled
SET2 = VCC, VSET1 = 0V, VSET0 = 0V3090µs
SET2 = VCC, VSET1 = 0V, SET0 = VCC13SET2 = VCC, SET1 = VCC, VSET0 = 0V1030
SET2 = VCC, SET1 = VCC, SET0 = VCC1030
Watchdog Input Pulse Width(Note 2)tWDIAfter WDO deasserted100ns
Watchdog Output Pulse WidthtWDOMAX6369/MAX6371/MAX6373100300ms
MAX6370/MAX6372/MAX637413ms
Internal Setup Time(Note 4)tSETUPAfter WDO deasserted300µs
Typical Operating CharacteristicsSUPPLY CURRENT
vs. TEMPERATURE
MAX6369/74-01
TEMPERATURE (°C)
SUPPLY CURRENT (µA)
VCC = +5.5V
VCC = +2.5V
WATCHDOG TIMEOUT PERIOD
vs. TEMPERATURE
MAX6369/74-02
TEMPERATURE (°C)
NORMALIZED WATCHDOG TIMEOUT PERIOD
MAX6369–MAX6374Pin-Selectable Watchdog Timers
Pin Description
PINNAMEFUNCTIONWDIWatchdog 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.GNDGroundN.C.Not Connected. Do not make any connection to this pin.SET0Set Zero. Logic input for selecting startup delay and watchdog timeout periods. See Table 1 for timing details.SET1Set One. Logic input for selecting startup delay and watchdog timeout periods. See Table 1 for timing details.SET2Set Two. Logic input for selecting startup delay and watchdog timeout periods. See Table 1 for timing details.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. VCCSupply Voltage (+2.5V to +5.5V)
SET2
SET1SET0
VCC
WDOGND
N.C.
WDI
SOT23TOP VIEW
MAX6369
MAX6370
MAX6371
MAX6372
MAX6373
MAX6374
Pin ConigurationMAX6369–MAX6374Pin-Selectable Watchdog Timers
Detailed DescriptionThe 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.
Table 1. Minimum Timeout Settings
LOGIC INPUTS MAX6369/MAX6370MAX6371/MAX6372MAX6373/MAX6374
SET2SET1SET0tDELAY, tWDtDELAY = 60s, tWD tDELAYtWD001ms1ms3ms3ms0110ms3ms3s3s1030ms10ms60s1s 11DisabledDisabledDisabledDisabled00100ms100ms200µs30µs011s300msFirst Edge1s 1010s3sFirst Edge10s1160s60s60s10s
MAX6369–MAX6374Pin-Selectable Watchdog Timers
