• State TI Thinks Resolved
  • Locked Locked
  • Replies 10 replies
  • Answers 1 answer
  • Subscribers 65 subscribers
  • Views 471 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TPS40056: Slow rise time of the part on a certain circumstance

Brayden Bae
Prodigy 10 points
Part Number: TPS40056

Dear. Ti engineering experts.

Always thanks for your effort and kindness for better quality and service.

Here is my question and details as below.

P/N : TPS40056PWP / TPS40056PWPR

Condition : Output  (-6V/15A) // Input (12V)

Details :  Our company applies this part to 3 applications. However, we detect that 2 out 3 is showing abnormal rising time.

               Under 15A Voltage, It takes too much rising time particularly within 5.8V - 6V (Abnoramlly slow rising time, 150ms)

               Under 0 or 50% Volage, It is measured as normal rising time (30ms)

               This symptom is not found on the parts made in this Jan, but found on the parts manufactured since this March.

               Approximately 10% of parts (produced after March) shows this symptom.

               What is causing this? What should we do to correct?

Normal rising time

Normal Rising time

Abnormal rising time

Abnormal Rising time

IC Peripheral Circuit

IC Pheripheral Circuit

  • 0
    TI__Expert 8245 points

    Hi,

    It looks the schematic is not clear, could you please upload a clear one? Thanks.

  • 0 in reply to Iven Su
    Prodigy 10 points

    Here it is. Thanks for your effort.

  • 0 in reply to Brayden Bae
    TI__Expert 8245 points

    Hi,

    It's recommended simply connect SS pin to GND to get a constant soft-start time, it's not clear what's the extra circuit connecting to another device in SS used for but you can monitor voltage on SS pin to see if there is a proper rise. If not you should take a look at the extra circuit. Thanks.

  • 0 in reply to Iven Su
    Prodigy 10 points

    Dear. Iven.

    Even after implementing your recommendations, same symptoms are still occuring for now.

    So, let me ask you further questions.

    1. May I know of place of origin of this part currently?
    The parts from Taiwan, D/C 09/12/20, 06/06/19, 06/15/19
    These three parts show abnormally slow rising time. What is the specific rule of setting D/C?

    2. Is the place of origin OR raw material of this part changed recently?
    Because it appears normal rising time when we replace the parts with old parts.

    Hope to receive a reply as soon as possible.

    Thanks for your effort.

  • 0 in reply to Brayden Bae
    TI__Mastermind 27470 points

    Hi 

    can you show the "good" part and "bad" part of Soft Start waveform?

    For the rules of D/C nad any row material change, I suggest you can contact disty or our Regional CQE, they will help you to figure out these two question.

    Thanks

  • 0 in reply to Daniel Li14
    Prodigy 10 points

    Hi, Daniel

    These are Soft Start waveform of normal part and abnormal part.

    1. Normal part (Condition : Output - Negative, Under -6V/15A)

    2. Abnormal part ( Condition : Output - Negative, Under -6V/15A)

    Thanks for your effort.

  • 0 in reply to Brayden Bae
    TI__Mastermind 27470 points

    Hi Brayden:

    Sorry that I did not describe it clear.

    I means the SS pin voltage, cause Vo(FB) should follow the SS PIN voltage to raise up. if there is some different, first step is we need check the SS pin voltage . My suspect is the leakage current at Q1 . 

    Thanks

    Daniel Li

  • 0 in reply to Daniel Li14
    Prodigy 10 points

    Dear. Daniel.

    There was not any change after adjusting SS pin voltage (to 3.7V)

    Over 50% of the parts with 19+ D/C show same symptom.

    What is causing this?

    Thanks for your effort.

  • 0 in reply to Daniel Li14
    Prodigy 10 points

    Dear. Daniel.

    When can I receive an answer or reply? Since this problem affects our business a lot, we must figure this out.

    Hope to get your advice as soon as possible.

    Thanks.

  • 0 in reply to Brayden Bae
    TI__Mastermind 27470 points

    HI Brayden:

    In normal statues, the FB will follow soft start voltage raising, only see the soft start dc voltage is not helping for the root cause, as we mentioned , pls help show the SS PIN voltage waveform at start up. 

    and in the same time, pls compare the COMP PIN waveform at start up see any difference. cause I also see external circuit adding at COMP pin . 

    Did you tried to use TPS40056 EVM to verify the "bad" part and "good part" ,cause if EVM have same issue, it should be caused by silicon. if the start up perform same at EVM, then it is external circuit cause this issue.

    Thanks