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TPS3808G01DBVEVM: TPS3808G01DBVR defective?

DHaas59
Prodigy 140 points
Part Number: TPS3808G01DBVEVM

CT=33nF,  VDD=3.3V,  /RESET pullup=100K@3.3V,

/MR pullup=5K@ 3.3V

SENSE voltage divider 665K/100K, sense deglitch cap=2.2uF(because 1nF was allowing glitch resets)

We have a group of TPS3808G01 parts that appear to be defective.  The /RESET either will not leave the reset state or the output driver appears to not be in saturation.  The /RESET voltage sometimes 2.7V with 100K pullup to 3.3V.  There is no other load on the /RESET pin other than the pullup.

The voltage on CT appears to be in some strange state on defective components.  When measured with DMM the voltage is commonly ~.7-.9 voltage.  I'm assuming this pin is controlled by a one shot multivibrator and once it hits the threshold voltage of 1.23V it resets to 0V on pin CT.  This 0V expected behavior is observed on parts functioning as expected but not on defective parts.

The SENSE voltage also is observed to be high on defective parts.  Expected behavior is for SENSE pin to be ~0.420 but defective parts are measuring ~1V on SENSE.

Is this due to leakage on SENSE and CT pins?  Are these factory defects or something in the design causing EOS damage.  The application appears to be in accordance with the datasheet with the exception of the 2.2uF on SENSE.  Is there a concern with excessive capacitance on SENSE?

  • 0
    TI__Genius 12630 points

    Hello,

    It sounds that these devices are defective because of the numerous issues you pointed out. The /RESET voltage should either be 0V or VDD when the device is powered on. The CT pin charges up to the expected threshold before resetting again as you mentioned but not what you are seeing. The sense pin should also be at the internal reference voltage of ~0.4V. Because you are seeing these issues on a certain group of parts, and not consistently with known good parts, it must be the devices themselves. How many devices are showing issues? Can you confirm the application works as expected with known good working devices? If yes, do you want to proceed with the formal Failure Analysis customer return process for the defective devices?

    -Michael

  • 0 in reply to Michael_DeSando
    Prodigy 140 points
    I do have one sample that is working with this configuration with the exception of .1uF on SENSE rather than 2.2uF. I don't really want to damage the one working unit I have. I have six loose parts removed from boards that are in a defective state. Yes, I'd like to return for FA if you don't have any known field issue that would explain this. I'm trying to get some purchase history since we probably bought these through Digikey.
  • 0 in reply to DHaas59
    TI__Genius 12630 points
    Please contact me via email at michaeldesando@ti.com

    I don't see any obvious problem with connecting a larger capacitor on the sense pin so I don't think this is the cause of the issue. I can start you on the failure analysis process once you send me an email.

    -Michael