How low must the watch dog start in UJA1078?

[jingfang]

we find that when SPI CLK has 507.5mV,the watch dog can not start.

How low must the watch dog start in UJA1078?

[guoweisun]

You can understand that Vhys means the difference of switching threshold value between the input voltage increase and decrease.

[jingfang]

Yes,according to the calculation,the switching threshold voltage is 0.6V(Vv1 = 5V), the value I measured is 0.5V,why is it considered to have a singal and no trigger watch dog?

[guoweisun]

Follow below picture connection:

[guoweisun]

Refer to below picture:

[jingfang]

I'm sorry to bother you.

Whether the pull-down resistance on the SCK&SCSN is required?

 

[guoweisun]

No, because to ensure that the SCSN pin and the SCK pin are always on a defined level the SBC
contains an internal pull-up resistor to V1 at SCSN and an internal pull-down resistor to
GND at SCK

[jingfang]

Vv1 = 5V -> Vth 1.5V~3.5V, minus Vhys -> min vaule is 0.6V，

Tha value I tested was 0.5V,which theoretically should not be consided singal,can you take a look at it?

[jingfang]

Use a minimum of 0.3*2.97 = 0.891V > 0.5075V,

so in theory watch dog should be start?

I have asked my guest to check the resistance. Is there any other place to check?

[guoweisun]

what's your actual V1 value in your schematic?

[jingfang]

The multimeter measured 5V.

[guoweisun]

The threshold should be 1.5V min,   0.5V can't be considered valid value.

[jingfang]

The result was that 0.5V did not trigger watch dog.

How can I slove this problem or are there any experiments I can try?

[guoweisun]

If you want to trigger this threshold which need at lease 1.5V ,so 0.5V can't trigger it which make sense.

[jingfang]

OK, at UJA1078,how low is the single level on SPI enough to trigger watch dog?

[guoweisun]

should be as 0.3*V1 to 0.7*V1

[jingfang]

If SPI doesn't have a communication,it won't feed the dog so ic will reset. 

The results of our experiment that SPI CLK measure 0.5V,but ic not reset.

Will the IC reset in the following range?

0~0.3V1

0.3~0.7V1

0.7~V1

[guoweisun]

should be 0.3-0.7 V1 and above 0.7V1