STWD100NY Connection

[tensaisakuragi06]

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.

[Peter BENSCH]

Er... you want to drive a relay directly connected to WDO, i.e. a mechanical relay with a coil and mechanical contacts?

What are the electrical parameters of this relay?

And you have read the data sheet, table 4, parameter VIL, and you also understand what R25/R26 do at pin /EN?

Regards
/Peter

[Andrew Neil]

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@tensaisakuragi06 wrote:

I attach my drawings below and needs your help.

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You omitted a key part of the drawing - you haven't shown how your relay is connected!

And, as @Peter BENSCH said, you need to give full details of the relay.

How to write your question to maximize your chances to find a solution

[tensaisakuragi06]

I use the WDO like microcontroller pin to drive, not to the coil. I also attach the relay connection. I put optional resistors to get precaution against if i left the EN floating and did not drive the STWD100. Because some of the parts in datasheet , left float and somewhere if EN remains high for instance. Its total my lack of inexperience of STWD100.

 

[tensaisakuragi06]

With your pointer i am not sure i can drive relay with WDO? because i did not see any parameter like Iwdo, max current value of WDO.

[Peter BENSCH · Accepted solution]

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.

[tensaisakuragi06]

I am plannig to use as 0R on R25 and R26. If IC works with EN floating, i did not put those resistors. To get trigger soruce from WDO, should not i left floating the EN pin? Currently i left the EN pin floating(did not put any resistor on R25 and 26). I will try shorting the R40.

[tensaisakuragi06]

I was plannig to left floating of EN du to this statement:

[Peter BENSCH]

The excerpt from the data sheet already gives you the answer to your last post.

[Andrew Neil]

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@tensaisakuragi06 wrote:

I am planning to use as 0R on R25 and R26.

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If you put 0R on R25 and R26 you will short your VCC supply to GND !