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tensaisakuragi06
Graduate
September 1, 2025
Solved

STWD100NY Connection

  • September 1, 2025
  • 11 replies
  • 934 views

I use STWD100NY Watchdog IC and for now, i can not achieve what i want. The problem is about to get output from the WDO pin. I did not connect the WDO to the MCU but i connect it to drive a relay. I set up my timer to 4 seconds. Even if it exceeds the twd time, i can not get the signal from WDO pin. I attach my drawings below and needs your help. My Vcc is 5V( most setups use 3.3v but i think that i can choose it 5V according to datasheet ). R25 and R26 resistors are optional.watchdog IC.png

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    Best answer by Peter BENSCH

    If you control /EN with a voltage divider of 1k+1k, the STWD100 will never work because this results in a voltage of VCC/2. However, as shown in table 4 mentioned above, /EN requires a voltage of max. 30% VCC to enable the STWD100. This means that as long as /EN is not activated, WDO cannot be active either.

    Incidentally, WDO is an open drain, which is why you have provided R134 as a pull-up. However, this also means that R40 is pointless and can be replaced by a short circuit.

     

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    tensaisakuragi06Author
    Graduate
    September 1, 2025

    Its my prediction that they will use it for the button with LED. I dont have any extra space to embed the watchdog relay. The only want to know that if there is a problem and this problem is caused by malfunctioning of the MCU. This IC comes into my mind for the solution. I don't want to recover IC, i just want to know if the malfunctioning is due to improper working of MCU. Maybe it is not suitable or the best way for that but for now, it satisfy my needs. If you suggest any other method, i will kepp them in my mind for future projects.

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