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TPS3828: It happened to reset without the set value

Hayashi
Expert 1840 points
Part Number: TPS3828

Hi team

When I check the device TPS3828-33 by the Stabilized power supply, it make the  /reset down.
Please let me know why it happen, if you know.
The atachment is waveform I checked the device.
The meaning of number is
2:VDD
3:/RESET
4:WDI
The /reset fall down particular when the WDI output the pulse.
Best regards
Hayashi
  • 0
    TI__Genius 10385 points
    Hayashi,

    I will be recreating your setup on the bench to see if I can get the same result. Please let me know of any more details about your setup that may helpful in replicating what you are seeing.

    Thanks for your patience,
    Ricardo
  • 0 in reply to Ricardo
    Expert 1840 points

    Ricardo san,

    I tested it with a circuit made of breadboard.
    And I will send new measurements with no problem device.
    In this case, there was no problem with reset operation, but the waveform of WDI periodically outputs pulses. Is this the problem behavior?
    This time, in the device which is a problem, it instantaneously falls to low as the pulse of this WDI like the waveform sent yesterday.

    Best regards
    Hayashi

  • 0 in reply to Hayashi
    Expert 1840 points
    Ricardo san,

    How is it?
    I'm worried that other devices will behave similarly like this.

    I'm waiting for your reply.

    Best regards
    Hayashi
  • 0 in reply to Hayashi
    TI__Genius 12630 points
    Hayashi,

    If you leave WDI open, the device generates its own internal WDI pulse to prevent the /RESET from activating to logic low. This is what you see in your last scope capture which is correct operation.

    When you apply a WDI signal, you must apply the WDI pulse within the watchdog timeout of 1.6 seconds or a /RESET event will occur. The WDI pulse must meet the requirements described in the datasheet otherwise a /RESET event will occur. The WDI pulse must be at least 0.7 * VDD and remain at this voltage for at least 10ns for the device to notice the pulse and prevent /RESET from activating to logic low. I don't think your WDI pulse amplitude reached at least 0.7* VDD in the first scope capture so I believe the /RESET is correct.

    Please let me know if you have any questions. Thank you!

    -Michael
  • 0 in reply to Michael_DeSando
    Expert 1840 points
    Michael san

    Thank you for your reply.
    Is it correct that I have understood as follows?
    In other word, the first capture is meaning that it is operation as expected because the pulse of WDI don't reach the 0.7 * Vcc.

    So, I have another question.
    1. the first scope and second is same circuit, but the only difference is the device.
    I think the each other WDI can't reach the 0.7 *Vcc.
    What the difference point do you think?

    2.If the WDI work is normal, I think the /RESET return wait for delay time.
    But, the first scope don't wait the time.
    How is it your opinion?

    Best regards
    Hayashi
  • 0 in reply to Hayashi
    TI__Genius 12630 points

    Hayashi san,

    1. You mention the first scope and second scope capture are same circuit but different device. Is WDI left open in either scope capture? Is the WDI signal the same for each circuit?

    2. If the WDI works as normal, the /RESET should wait for delay time upon return. You are correct. It looks like the delay is very short since the time scale on the scope capture is 5us / division. Is this correct? The /RESET should remain low for approximately 200ms. Is anything else connected to /RESET pin?

    3. I would like to know how many devices you have tested, and if the issue occurs everytime? Can you also try to reduce the VDD capacitor to 0.1uF?

    -Michael

  • 0 in reply to Michael_DeSando
    Expert 1840 points
    Michael san

    Thank you for your supports.
    I answer your questions.

    1.Is WDI left open in either scope capture? Is the WDI signal the same for each circuit?
    -> Yes, it is same circuit and the WDI is opened.

    2.I think the /RESET is very short you told. This pin connected the pull up to VCC like the regarding the head circuit.

    3.This case is only 1 device. Do you think it is the defective product?After,I will check the capacitor changed to the 0.1uF.

    Best regards
    Hayashi
  • 0 in reply to Hayashi
    TI__Genius 12630 points

    Hayashi san,

    Because the /RESET is such a short delay, this could be a defect. I would like to know the result when decreasing the capacitor. When the WDI pin is floating, the watchdog disables and the scope capture should be similar every time.

    Do you have another device you can try to see if it is defected device or problem with your application or circuit board?

    -Michael

  • 0 in reply to Michael_DeSando
    Expert 1840 points
    Michael san

    I will check the waves the capacitors changed.

    And, I check the circuit by solderless board.
    It does not occur as operation, when changing from the circuit on which the target device is mounted to the normal product.
    Regarding the number, we have confirmed about three ordinary devices.

    -Hayashi