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TPS3809: TPS3809 Output Oscillation

Part Number: TPS3809

Hi team,

  My customer is using TPS3809K33 and met an issue regarding to output oscillation.

  I took it back set it up in TI lab as below:

  The VDD of TPS3809 is connected to a external power supply. When I manually rotate and increase the input voltage and when the input voltage hit around 2.93V, tps3809 output unstable. The waveform is attached. However when I increase the input voltage in much faster slew rate, the output is normal. It almost like the device enters in a hystersis loop and never get out.. (yellow is the VDD pin, red is Reset pin)

  I wonder what's the mechanism behind the behavior? Thanks.

Regards,

Patrick

  • Patrick,

    Is there a 0.1uF decoupling capacitor next to VDD pin to GND? This is recommend in Note 2 under the electrical characteristics table on page 3 of the datasheet and will help with the monitoring stability.

    Please let me know if there is already a decoupling capacitor at the input and then we can investigate further. Also if there is anything else connected to the VDD or /RESET pins, please describe. Thanks.

    -Michael
  • Hi Michael,

      Thanks for supporting the case.

      There's 0.1uf cap between VDD and GND and it's placed very close to the pin. I've re-created the behavior with or without the cap. I've also tried different samples with the same behavior. I don't think it's related to external application. Can you check with your team on how the device is designed under this cocndition? Thanks.

    Regards,

    Patrick

  • Patrick,

    I have spoke to my team and we have never seen or heard of this behavior before. And this is an older device so we would have expected to see a return before if this was a device issue. The weird part is that the /RESET output looks to be oscillating every 7 ms but the /RESET delay is 200 ms. So in no circumstance should the output be transitioning the way it is in the scope capture. I am going to try to replicate this behavior on the bench and let you know what I find.

    Can you provide the schematic to my email? michaeldesando@ti.com

    We will work to get this figured out ASAP. Thanks!

    -Michael
  • Patrick,

    After my bench testing, I was not able to replicate the issue. I tried ramping verrrrry slowly and also fast, and the output came up and remained high and stable. I confirmed with multimeter measurement and also with oscilloscope. Because the device is older and we have not seen this issue before, I am confident that it is not a TPS3809 issue unless the device is damaged. I will need more information regarding your test setup, test conditions, schematic, and any other useful information. Email me at michaeldesando@ti.com

    Thanks!
    -Michael