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TPS3851: Why sometimes RESET pin or WDO pin of TPS3851G25EDRBR will be low level for a long time?

Lian Wu
Genius 5250 points
Part Number: TPS3851

Dears:

We use TPS3851G25EDRBR in our Board, and the bord work well in normal temperature.

These days we made some boards working under 50℃~70℃ temperature, and we found an issue about it.

Sometimes RESET pin or WDO pin of TPS3851G25EDRBR will be low level for a long time, then we tested the watching Power's and MR's Voltage they are all high level.

Why it happend?

Pls. kindly help to give some advice, thanks a lot!

And pls. kindly help to check the schematic as below picture:

Thanks a lot!

Best regards

Luck Wu

  • 0
    TI__Genius 12630 points

    Luck Wu,

    There are some issues I see.

    1. The Pull-up resistor for /RESET and /WDO should be between 1kohm and 100kohm. In the schematic it says 100.

    2. SET1 should be GND if not using Watchdog. Is the Watchdog being used?

    3. /MR pin should be pulled high but it looks like you have /MR connected to 3 different inputs?

    What is the intended use of this device? Is it voltage monitor and watchdog monitor?

    -Michael

  • 0 in reply to Michael_DeSando
    Genius 5250 points

    Hi Michael:

    We check our shematic again, and answer your questions:

    1. The Pull-up resistor for /RESET and /WDO should be between 1kohm and 100kohm. In the schematic it says 100.

           Luck:Our design is 100Kohm, and you can see R248;

    2. SET1 should be GND if not using Watchdog. Is the Watchdog being used?

          Yes, Watchdog is used.

           Luck:SET1 is connected GND since R532 is 0o.

    3. /MR pin should be pulled high but it looks like you have /MR connected to 3 different inputs?

            Luck:We deign /MR is pulled high in other sheet.

    What is the intended use of this device? Is it voltage monitor and watchdog monitor?

            Luck: The device is used for voltage monitor and watchdog monitor.

    Could you kindly help to give some other advice?

    Thanks a lot!

    Best regards

    Luck Wu

  • 0 in reply to Lian Wu
    TI__Genius 12630 points
    Luck Wu,

    2. SET1 to GND disables watchdog but you say you are using watchdog. SET1 should be "high" to use watchdog.


    Also, please provide some captures for VDD, WDI, /RESET and /WDO so I can see what the issue looks like.

    -Michael
  • 0 in reply to Michael_DeSando
    Genius 5250 points
    Hi Michael:
    These days we found there is voltage pulse for an instant under 50℃~70℃ temperature.
    However, we can not capture the pulse'wave, and is the reason to generate the issue?
    Btw, what is about captures? Could you kindly give some examples for us?
    And we will give you ASAP.
    Thanks a lot!

    Best regards!
    Luck Wu
  • 0 in reply to Lian Wu
    TI__Genius 12630 points
    Luck Wu,

    By captures I talking about Oscilloscope captures that show the signals over time during the issue. You connect scope probes to the pins in question and trigger the capture when the issue occurs. These will be helpful for us to see what exactly is happening. Try to show the voltage pulse. Thanks!

    -Michael
  • 0 in reply to Michael_DeSando
    Genius 5250 points
    Hi Michael:
    Now we can not get the captures, and we are trying to use some other methed to test it.
    Btw, is there any other customer meet the issue if there is voltage pulse?

    Thanks a lot!
    Luck Wu
  • 0 in reply to Lian Wu
    TI__Genius 12630 points

    Luck Wu,

    No we have not heard of this issue before. The scope captures will help us determine the problem.

    -Michael