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TPS3851: TPS3851G18EDRBR : Reset is happening when WDI is toggled with 250ms ON time and 1s OFF time

Surya DS
Prodigy 60 points
Part Number: TPS3851

Team,

We have used TPS3851G18EDRBR in our design to provide Reset for controller for every 17 seconds by choosing 0.22uF for CWD pin.

When we toggle the WDI input with 250ms ON time and 1 s OFF time continuously from a controller, Reset is still happening .

But , when we toggle the WDI input with 300mS ON time and 5s OFF time continuously, Reset is not happening. In your datasheet , it was mentioned WDI minimum pulse duration as 50ns , in that case the device should not reset for the first mentioned time durations.

Also , we have combined WDO and RESET pin which was given to the Controller's Reset pin.

Why the device is behaving like that?

Regards

Surya D S,
System Engineer,

Data Patterns Private Limited.

  • 0
    TI__Genius 9375 points

    Hi Surya,

    You are correct in that these events should not differ in how they occur. Do you have a schematic and a scope shot of what is occurring regarding timing?

    Thanks,
    Abhinav.

  • 0 in reply to Abhinav.Sharma
    Intellectual 420 points

    Hi,

    Sorry for the delay, Regards of our colleague Mr. Surya I want to continue the issue here.

    I have attached the requested watchdog reset section schematic for your review.

    Here we are facing two different issues. We have used the same watchdog circuit in two places.

    1. When we increase the WDI ON time from 250ms to 350ms & OFF time duration from 1Sec to 5Sec (in one of circuit) the WDO reset is working properly.

    But with the previous WDI ON time of 250ms & OFF time duration of 1Sec itself, If we place any scope probe or DMM probes (Even Floating) at WDI Pin then WDO Reset is working properly. This is one scenorio.

    2. In our another similar circuit (board) without any component changes, Even if we increase the WDI ON time to 350ms & OFF time to 5Sec, The WDO reset is not working and randomly giving Reset even-though WDI input is proper.

    But in this circuit also If we place any scope probe or DMM probes (Even Floating) at WDI Pin then WDO Reset is working properly.

    We are not sure what could be causing these issues and issue is also not consistent (Sometime Random). So please review and suggest a solution to resolve this issue.

  • 0 in reply to Sugumar Krishnasamy
    TI__Genius 9375 points

    Hi Sugumar,

    I'll get back to you on this after reviewing and speaking with another product expert.

    Thanks,
    Abhinav.

  • 0 in reply to Abhinav.Sharma
    Intellectual 420 points

    Hi,

    I have raised a new query (Due to delay in response) and the link is given below, Where I have updated the recent test results and behavior of the issues.

    You can refer the same for more details.

  • 0 in reply to Sugumar Krishnasamy
    TI__Genius 9375 points

    Hi Sugumar, I will close this thread since the other thread is the new line of communication.

    Thanks,
    Abhinav.