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 Priced to Clear Propagation Delay Test Condition Width
RS Stock No. 168-6421
Mfr. Part No.STWD100NYWY3F
£0.26
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
RS Stock No. 686-7509
Mfr. Part No.STWD100NYWY3F
£0.646
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
RS Stock No. 900-9863
Mfr. Part No.TPL5010DDCT
£0.666
Each (In a Pack of 5)
Units
SOT-23 1 6 1.8 V 5.5 V +105 °C -1mA 1mA 3.05 x 1.75 x 1mm 1mm 3.05mm Yes 50pF 1.75mm
RS Stock No. 162-9880
Mfr. Part No.TPL5010DDCT
£0.429
Each (On a Reel of 250)
Units
SOT-23 1 6 1.8 V 5.5 V +105 °C -1mA 1mA 3.05 x 1.75 x 1mm 1mm 3.05mm - 50pF 1.75mm
RS Stock No. 900-9867
Mfr. Part No.TPL5110DDCT
£0.666
Each (In a Pack of 5)
Units
SOT-23 1 6 1.8 V 5.5 V +105 °C -1mA 1mA 3.05 x 1.75 x 1mm 1mm 3.05mm - 50pF 1.75mm
RS Stock No. 162-9881
Mfr. Part No.TPL5110DDCT
£0.429
Each (On a Reel of 250)
Units
SOT-23 1 6 1.8 V 5.5 V +105 °C -1mA 1mA 3.05 x 1.75 x 1mm 1mm 3.05mm - 50pF 1.75mm
RS Stock No. 165-5639
Mfr. Part No.STWD100PYW83F
£0.297
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
RS Stock No. 829-1513
Mfr. Part No.STWD100PYW83F
£0.493
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
RS Stock No. 860-7435
Mfr. Part No.STWD100NWWY3F
£0.223
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
RS Stock No. 165-5301
Mfr. Part No.STWD100NWWY3F
£0.219
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
RS Stock No. 168-6420
Mfr. Part No.STWD100NPWY3F
£0.232
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
RS Stock No. 686-7506
Mfr. Part No.STWD100NPWY3F
£0.592
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
RS Stock No. 860-7479
Mfr. Part No.STWD100YNWWY3F
£0.301
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
RS Stock No. 165-5302
Mfr. Part No.STWD100YNWWY3F
£0.293
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
RS Stock No. 165-5640
Mfr. Part No.STWD100YNPWY3F
£0.296
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
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