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LM5025A: LM5025A Application question check

Sulyn ZHANG
Expert 8700 points
Part Number: LM5025A

Hi Team,

My customer is using our LM5025A in new project. But in this project, the Vin voltage will be in the range of 8V to 90V and this is un-avoidable due to some reason. However, in our datasheet, we recommend that Vin =13V to 90V. So for this situation, can some expert let me know what will LM5025A behavior if the vin is as low as 8V?  We want to see the risk or potential issue for this, then see if some solution to resolve this.

Best regards,

Sulyn

  • 0
    TI__Expert 8700 points

    Hi Team,

    Would any expert can help give some suggestion for this? Thanks

    Best regards

    Sulyn

  • 0 in reply to Sulyn ZHANG
    TI__Expert 3095 points
    Hi Sulyn,
    I can see two potential issues:
    1) If VIN is 8V and VCC is higher than 8V then the internal body diode of the start-up regulator MOSFET will conduct. This may easily be prevented using external diodes to ensure that the VIN pin cannot drop much below VCC.
    2) Over temperature the UVLO threshold for this part looks like 7.87V - 7.18V. The part may not start if supplied from an 8.0V input due to the minimum drop across the start-up linear regulator. We can ask the IC designers this question if you wish, but it may take some time to get an answer.
    Thanks
    Joe Leisten
  • 0 in reply to Joe Leisten
    TI__Expert 8700 points
    Hi Joe,
    Thanks a lot for your support, this make me more clear. If possible, would you pls help check this with designer? Thanks. As customer is planning to MP very soon and have concern on this.

    Best regards,
    Sulyn
  • 0 in reply to Sulyn ZHANG
    TI__Expert 3095 points
    Hi Sulyn,
    The following comments come from our design manager. I will keep you posted once more information arrives.
    Thanks
    Joe Leisten

    "I do not know this device and I am trying to recover the database.
    I just read the datasheet and your comments got the main points:
    1. they need to avoid conduction between VCC and VIN pins through the device
    • you are right but I do not know if it is necessary because looking to datasheet you could have as recommended operating condition VCC=15V and VIN=13V (VCC>VIN)
    I need to double check on schematic.
    2. The part may not start if supplied from an 8.0V input.
    • On this point I think you are right. Looking to datasheet number with 8V on VIN we cannot guarantee device start-up because VCC could be lower than VCC undervoltage lockout threshold
    • In this moment I cannot estimate the drop on start-up linear regulator.
    Moreover I do not believe that we can guarantee performance of start-up regulatore below 13V

    I will update you as soon as I recover the database and I can look the schematics."
  • 0 in reply to Joe Leisten
    TI__Expert 3095 points
    Hi Sulyn,
    This is the reply that I have from design:

    "I can confirm that between VIN and VCC we have a linear regulator with a typical drop of about 3.5V.
    If VIN is below 13V we cannot guarantee start-up."

    I hope this answers your question.
    Thanks
    Joe leisten