• State TI Thinks Resolved
  • Locked Locked
  • Replies 3 replies
  • Answers 1 answer
  • Subscribers 63 subscribers
  • Views 620 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.

LM5022: LM5022 startup current

Wei-Hao Chen (TW-FAE)
Expert 3260 points
Part Number: LM5022
Other Parts Discussed in Thread: LM5021

Hi team,

my customer is using LM5022 to design an offline flyback converter. They want to know what is the startup current for LM5022? They need to calculate required startup current and HV startup resistor value.

Thanks.

Best Regards,

Wei-Hao

  • 0
    TI__Guru* 78240 points
    Hi Weihao,

    What do you mean by start up current? And what is HV startup resistor? If you mean the inrush current, it is determined by the input capacitor, output capacitor, transformer, soft-start capacitor, and the load tied to the output during startup. The LM5022 controls the SS to limit the inrush, but mostly it is the external circuit design, not the LM5022 itself.

    Thanks,
    Youhao
  • 0 in reply to Youhao Xi
    TI__Expert 3260 points

    Hi Youhao,

    The required current for the controller when VIN is below UVLO. For the offline isolated DC/DC converter, controller needs draw current directly from the HV line, it needs HV resistor to limit the current to charge the VIN cap and supply the current to controller.

    Please refer to LM5021 as a example:

    This current will determine how big of the HV startup resistor can be used.

    Thank you.

    Best Regards,

    Wei-Hao

  • 0 in reply to Wei-Hao Chen (TW-FAE)
    TI__Expert 3260 points
    Hi Youhao,

    Any update on this?

    Cheers.

    Best Regards,
    Wei-Hao