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TPS25926: EN pin 1.47V Vout only 3.3-3.6V, Vin = 12V

Oliver Lin
Expert 4475 points
Part Number: TPS25926

Tool/software:

Hi team,

My customer mentioned they found a status on this device. EN voltage is around 1.47V. But Vout is only 3.3-3.6V. Looks like not fully turn on. After changing EN to 2V, they can get 12V output

  • May I know why even VEN is over 1.44V listed in datasheet, but the FET is not fully turn on? What I think of this might be out of normal distribution. Please comment if my understanding is correct.
  • Another thing is why our device will present partially on? I thought that is a hard thresold to be fully on.

Thanks,

Oliver

  • 0
    TI__Mastermind 38835 points

    Hi Oliver,

    • How accurate are the measurements?
    • Is it repeating with multiple devices?
    • Any waveform?

    Yes, EN should not cause any intermediate state. I suspect output caps are getting charged from previous correct turn on or during this attempt, they charge and then due to some reason device fails startup. To confirm this or to get some more insight, waveform will be very helpful. Vin, Vout and current through the device for both EN = 1.47V and higher value.  

    Best Regards,
    Arush

  • 0 in reply to Arush Gupta
    TI__Expert 4475 points

    Hi Arush,

    I also asked custome to share waveform, but the boards are in their factory side. They are using digital multi meter to measure this. I asked them to get EN to 2V, then output is all good. That might take some time for the actual waveform.

    Have you ever met this kind of partially on case before?

  • 0 in reply to Oliver Lin
    TI__Mastermind 38835 points

    Hi Oliver,

    EN pin itself should not cause this type of behavior. Internally it is input of a comparator so voltage value should not cause intermediate output value. I have seen intermediate output value cases when gate of FET is not charged fully due to some leakage at dvdt pin. (probing this pin without appropriate impedance can also cause it to not ramp up to full value)

    Can you ask them for schematic and to check if they see any leakage path at dvdt pin or are they probing the dvdt pin when checking the enable pin threshold.

    Also, is this repeating with multiple devices/boards.

     

    Best Regards,
    Arush