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LM5022: Problems at temperatures below 0°C

ArTzy
Genius 15059 points
Part Number: LM5022

Hi Experts,

Seeking your assistance on this query from Cx:

We use the LM5022 in several products and it works so far. Now we have carried out a temperature test on the entire device and the driver started to have problems from around 0°C. The duty cycle at the exit has become smaller and smaller. If the driver was changed, the problem could not be reproduced. Therefore, the question arises whether this is an individual case or whether such problems are known with the LM5022MM.

Thank you.

Regards,
Archie A.

  • 0
    TI__Mastermind 47141 points

    Hi Archie,

    thank you for using the E2E forum.

    So far i have not heard about such an issue.

    Can you try to put the falling device on another board to check if this issue follows the device?

    Best regards,

     Stefan 

  • 0 in reply to Stefan Schauer
    TI__Genius 15059 points

    Hello Stefan,

    Apology for the delayed response as Cx just responded:

    The component was also re-soldered and the error also occurred. The error could not only be corrected in the climatic chamber but also externally with a cold spray.

    Thank you.

    Regards,
    Archie A.

  • 0 in reply to ArTzy
    TI__Mastermind 47141 points

    Hi Archie,

    I am not sure if I got all info right. So please confirm or correct below statements:

    - the error happens at lower temp only?

    - how can the error be corrected with cold spray?

    - you replaced the LM5022 with another one and the problem is still the same

    - how many boards do show this problem?

    - do you also have boards which do not show this problem?

    Best regards,

     Stefan

  • 0 in reply to ArTzy
    TI__Mastermind 47141 points

    Hi Archie,

    I am not sure if I got all info right. So please confirm or correct below statements:

    - the error happens at lower temp only?

    - how can the error be corrected with cold spray?

    - you replaced the LM5022 with another one and the problem is still the same

    - how many boards do show this problem?

    - do you also have boards which do not show this problem?

    Best regards,

     Stefan

  • 0 in reply to Stefan Schauer
    TI__Genius 15059 points

    Hello Stefan,

    Thanks for your support. Cx responded:

    [1]yes, as soon as the temperature is at 0°C or below, the driver no longer works cleanly.

    [2]The problem was first noticed in the climate chamber. For further investigations, the fault could then also be found with the cold spray.

    [3]I have replaced the faulty LM5022 and the error has disappeared. For further tests, I soldered in the faulty driver again and the error reappeared.

    [4]This problem has only occurred once. However, our power supply units are not normally operated at such.

    Regards,
    Archie A.

  • 0 in reply to ArTzy
    TI__Mastermind 47141 points

    Hi Archie,

    so far, I have not heard about that behavior and any weakness in that area. 

    You said the duty cycle becomes smaller and smaller, this means that also the Voltage goes down - right?

    Does this gradually go down with decreasing temperature or just starts to go down and a certain temperature and stops even when the temperature is not changed any more.

    Best regards,

     Stefan

  • 0 in reply to Stefan Schauer
    TI__Genius 15059 points

    Hello Stefan,

    Cx responded:

    At a certain temperature, the duty cycle begins to decrease. Thus, the output voltage also starts to drop until an error is triggered.
    If the temperature rises above a certain value, the duty cycle also increases.

    Regards,
    Archie A.

  • 0 in reply to ArTzy
    TI__Mastermind 47141 points

    Hi Archie,

    it would be good to see a scope plot of the COMP and FB pin at a working and failing condition.

    Best regards,

     Stefan

  • 0 in reply to Stefan Schauer
    TI__Genius 15059 points

    Hello Stefan,

    Please see the file shared below, for the snapshots:

    Temperature problem with LM5022MM driver.pdf

    Thank you.

    Regards,
    Archie A.

  • +1 in reply to ArTzy
    TI__Mastermind 47141 points

    Hi Archie,

    thank you for the report.

    When going through it had some issues with understanding all the information.

    May you can help to understand:

    - Page 6: Scope plot shows Gate supply L1 LS - where can i find this node in the schematic

    - Page 6: Ch2 and Ch3 show the same signal - Channel 2 shows a ripple of 8V - i would expect to see that on Channel 3 as well.

    This issue was only seen with one device - is this right?

    Another point: the schematic does not show a snubber for the Flyback primary winding - is this correct? This will lead to very high voltage peaks due to the leakage inductance.

    Best regards,

     Stefan

  • 0 in reply to Stefan Schauer
    TI__Guru 60265 points

    Hello Archie,

    As we did not hear back from you, I expect the issue is solved and I will close this thread now. Please post below or start a new thread for further questions.

    Best regards,
    Brigitte