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Original question:

TPS3823: Watchdog

TPS3823: Abnormal Operation Mode

Matt Qi
Expert 4510 points
Part Number: TPS3823

Hi team,

My customer found that our TPS3823 works abnormally:

WDI and RESET pin are both low-voltage level.

MR is the high-voltage level.

As a result, the output of the chip is abnormal and affects the normal function of the board signal.

The related schematic and waveforms are attached.

Could you please help take a review, and give any advice that what is the root cause that can result in this phenomenon?

https://e2e.ti.com/cfs-file/__key/communityserver-discussions-components-files/196/Waveform-Signal.7z

https://e2e.ti.com/cfs-file/__key/communityserver-discussions-components-files/196/Schematic.7z

Thanks for your time and effort.

Best Regars,

Matt.

  • 0
    TI__Mastermind 18710 points

    Hi Matt, 

    Could they please also provide a scope shot of the Vdd with the RESET and MR. Also what is the full part number of the device that they are using? I am suspecting that the device VDD is detecting a voltage below the device threshold. Another possible culprit is that the GPIO is sinking too much current, preventing the RESET pin to go high. That can be tested by replacing a 10kohm for R553.

    Jesse 

  • 0 in reply to Jesse Villanueva
    TI__Expert 4510 points

    Hi Jesse,

    First, the full part number is TPS3823-33DBVR.

    Second, the updated waveforms are attached. (VDD with RESET and MR). with the original R553 resistor value and updated value(10kOhm).

    https://e2e.ti.com/cfs-file/__key/communityserver-discussions-components-files/196/The-related-signal.7z

    Thanks for your time and effort.

    Best Regards,

    Matt.

  • 0 in reply to Matt Qi
    TI__Mastermind 18710 points

    Hi Matt,

    From the images, it does look like that the R553=10k helped. Depending on the amount of current being sinked by the GPIO, the R553 value can be increased.

    Jesse 

  • 0 in reply to Jesse Villanueva
    TI__Expert 4510 points

    Hi Jesse,

    We have increased R553 to 47k, and the output of the reset pin increase to 980mV, and we continue to increase the reset pin to 2MOhm, the reset is still 920mV.

    Then we tried to remove R553, the reset pin's output is still 880mV.

    We think R553 cannot help, do you have any other solution?

    Thank for your time and effort.

    Best Regards,

    Matt 

  • 0 in reply to Matt Qi
    TI__Mastermind 18710 points

    Hi Matt,

    Would it be possible for you to configure the A11 GPIO to an high impedance input to help reduce the current being sinked by the pin.

    Jesse 

  • 0 in reply to Jesse Villanueva
    TI__Expert 4510 points

    Hi Jesse,

    We have removed R553, the RESET pin still output 880mV.

    Thus, it is not related with A11 GPIO anymore. It is with our chip itself.

    Do you have any other solution?

    Thanks for your time and effort.

    Best Regards,

    Matt.

  • 0 in reply to Matt Qi
    TI__Mastermind 18710 points

    Hi Matt

    It may be possible that the device may have been damaged at this point, but another thing that could cause an issue is the R2160. A pull-up resistor is not necessary for the TPS3823 since it is a push pull device.

    Jesse 

  • 0 in reply to Jesse Villanueva
    TI__Expert 4510 points

    Hi Jesse,

    We think that maybe the drive capability of the RESET pin is not enough in the case of the TPS3823-33.

    Because the endpoint of RESET in this application is the Ethernet PHY and switch chip, whose reset rising/falling time is very short. So I think the current drive capability is very important. And the competitor's drive capability is 20mA.

    Could you please help recommend a p2p substitute for TPS3823-33? whose RESET drive capability is better. Like mA level.

    Best Regards,

    Matt. 

  • 0 in reply to Matt Qi
    TI__Mastermind 18710 points

    Hi Matt,

    Unfortunately, we do not have a P2P alternate for the TPS3823.

    Jesse