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.

[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.

 

[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.

[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.

[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 !

 

[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.

[tensaisakuragi06]

My bad, you re right i did not put any resistor but when writing here, i write as "planning to put 0R". By the way when changing the relay resistor, i am so close to my plan, when everything works well, IC reset itself by the help of WDI. By external pull-ups, i can drive relay at normal conditon. The remaining problem is this: when i adjust my timer to 2 sec, every transition, WDO toggles. I dont want the toggling process (i set up timer to high value to test if IC works). I attach a video related with that. The logic to latch the WDO confuses me.

[Andrew Neil]

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@tensaisakuragi06 wrote:

The remaining problem is this: when i adjust my timer to 2 sec, every transition, WDO toggles. I dont want the toggling process

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That seems consistent with what the datasheet says:

 

So the WDO gives a pulse output with a width between 10us and 280ms.

Are you wanting it to stay asserted permanently once the watchdog has "fired" ?

[tensaisakuragi06]

If i am not wrong, this situation happens because of my testing way. I think that relay can not toggle if MCU really crash.

[Peter BENSCH]

Well, the question is, why are you going to all this trouble to control a relay with a watchdog?

A watchdog is there to reset a device (typically an MCU or MPU) when there are no signs of life, thereby bringing the device out of the ‘death zone’. A relay is rather unsuitable as an intermediary. What is being controlled by the relay?

[tensaisakuragi06]

Its depending on the need. I do not want to recover the IC but somehow want to know if is fine or not. I use it for different purpose rather than the actual  aim.

[tensaisakuragi06]

Relay is used for just give a warning with its led indication.

[Andrew Neil]

If it's just an LED, why do you need a relay?

The STWD100NY can easily drive an LED directly!