Automotive watchdog in a five-pin SOT-23
The STMicroelectronics STWD100YNXWY3F is a single-channel watchdog circuit designed for automotive and industrial systems that need a supervised reset on a microcontroller or SoC. It asserts a reset output (active low, open-drain) when the watchdog input is not toggled within the timeout window, and holds reset for a minimum of 71 ms after the input resumes.
The 71 ms minimum reset timeout is the guaranteed period the output stays low after the watchdog condition clears. This gives the monitored device time to complete its internal reset sequence — typically a few milliseconds for a microcontroller's oscillator startup and register initialization — before the watchdog output releases. If the system's power-on reset or brown-out circuit uses a shorter timeout, the watchdog may release before the MCU is ready, causing a spurious early start. The 71 ms floor is generous enough to cover most automotive MCU reset sequences without needing an external delay.
The RoHS3 compliance also aligns with current environmental regulations.