Watchdog Timers

Watchdog timers (WDT) or sometimes referred to as computer operating properly or COP timer is a piece of hardware which can be found in embedded system applications but are an external component to the processor. Watchdog timers are commonly used in environments where human access is very limited or incapable of responding to faults in a timely mode, therefore, the system needs to be self-reliant if it hangs. An example would be a space probe, where human intervention is restricted when in operation if the device is unable to recover from malfunctions, it would become disabled.


What is the purpose of a Watchdog timer?


The purpose of the Watchdog timer (WDT) is to automatically detect pulse signals from a processor within a definite time period. The device will send a reset trigger if the system malfunctions or if the signal is not received and requires a reboot, this could occur because of software or hardware issues.


There are two ways in which a Watchdog Timer enable embedded system to be self-reliant:


• By detecting system errors which can include programming errors, a surge of power, software loops or hanging and if code crashes.


• By resetting operating systems and continuing normal program actions through the reset signal which is embedded in a Central Processor Unit (CPU) or Microcontroller.


What is a typical application of a Watchdog timer?


A watchdog timer (WDT) is used in everyday applications, such as digital TVs, washing machines, vacuum cleaner, microwaves, drones, grid metering to motor control systems such as cruise control, smartphones to name a few. Within all these devices, the functionality of a Watchdog Timer will provide the same or similar purposes.


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Description Price Package Type Number of Internal Timers Pin Count Minimum Operating Supply Voltage Maximum Operating Supply Voltage Maximum Operating Temperature Maximum Low Level Output Current Maximum High Level Output Current Dimensions Height Length Propagation Delay Test Condition Width Minimum Operating Temperature
RS Stock No. 168-6421
Mfr. Part No.STWD100NYWY3F
TWD12.70
Each (On a Reel of 3000)
units
SOT-23 1 5 - - +125 °C - - 2.9 x 1.6 x 1.05mm 1.05mm 2.9mm - 1.6mm -40 °C
RS Stock No. 165-5301
Mfr. Part No.STWD100NWWY3F
TWD12.80
Each (On a Reel of 3000)
units
SOT-23 1 5 2.7 V 5.5 V +125 °C - - 3 x 1.75 x 1.3mm 1.3mm 3mm - 1.75mm -40 °C
RS Stock No. 686-7506
Mfr. Part No.STWD100NPWY3F
TWD18.20
Each (In a Pack of 5)
units
SOT-23 - 5 - - +125 °C - - 2.9 x 1.6 x 1.05mm 1.05mm 2.9mm - 1.6mm -40 °C
RS Stock No. 829-1513
Mfr. Part No.STWD100PYW83F
TWD20.60
Each (In a Pack of 10)
units
SOT-323 1 5 2.7 V 5.5 V +125 °C - - 2.2 x 1.35 x 1mm 1mm 2.2mm - 1.35mm -40 °C
RS Stock No. 165-5640
Mfr. Part No.STWD100YNPWY3F
TWD15.50
Each (On a Reel of 3000)
units
SOT-23 1 5 2.7 V 5.5 V +125 °C - - 3 x 1.75 x 1.3mm 1.3mm 3mm - 1.75mm -40 °C
RS Stock No. 168-6420
Mfr. Part No.STWD100NPWY3F
TWD11.50
Each (On a Reel of 3000)
units
SOT-23 - 5 - - +125 °C - - 2.9 x 1.6 x 1.05mm 1.05mm 2.9mm - 1.6mm -40 °C
RS Stock No. 860-7479
Mfr. Part No.STWD100YNWWY3F
TWD23.20
Each (In a Pack of 10)
units
SOT-23 1 5 2.7 V 5.5 V +125 °C - - 3 x 1.75 x 1.3mm 1.3mm 3mm - 1.75mm -40 °C
RS Stock No. 165-5639
Mfr. Part No.STWD100PYW83F
TWD12.90
Each (On a Reel of 3000)
units
SOT-323 1 5 2.7 V 5.5 V +125 °C - - 2.2 x 1.35 x 1mm 1mm 2.2mm - 1.35mm -40 °C
RS Stock No. 860-7435
Mfr. Part No.STWD100NWWY3F
TWD23.20
Each (In a Pack of 10)
units
SOT-23 1 5 2.7 V 5.5 V +125 °C - - 3 x 1.75 x 1.3mm 1.3mm 3mm - 1.75mm -40 °C
RS Stock No. 165-5302
Mfr. Part No.STWD100YNWWY3F
TWD19.70
Each (On a Reel of 3000)
units
SOT-23 1 5 2.7 V 5.5 V +125 °C - - 3 x 1.75 x 1.3mm 1.3mm 3mm - 1.75mm -40 °C
RS Stock No. 686-7509
Mfr. Part No.STWD100NYWY3F
TWD23.80
Each (In a Pack of 5)
units
SOT-23 1 5 - - +125 °C - - 2.9 x 1.6 x 1.05mm 1.05mm 2.9mm - 1.6mm -40 °C