• State
  • Locked Locked
  • Replies 5 replies
  • Subscribers 63 subscribers
  • Views 534 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.

LM5122 UVLO can't shut down the power supply

Kenny Ding
Prodigy 80 points
Other Parts Discussed in Thread: LM5122, LM5121

I have a question regarding the UVLO feature of the LM5122 EVM. When I pull UVLO to GND, I expected the controller shut down as the datasheet indicates and Vout should be 0V. But on my test, Vout is almost same as Vin. The high side switch is always on. I tried different modes, the results are the same. I want to use the UVLO as the on/off control pin, but it seems not working that way. Can you please explain?

  • 0
    TI__Guru 58941 points

    Hi

    When the IC is in shutdown, there is no switching and the output voltage becomes almost same voltage as the input since boost converter has a pass from the input to the output through high-side MOSFET.

    If you want to see the output voltage be 0V in shutdown, please use LM5121 rather than LM5122.

    Regards,

     

     

  • 0 in reply to EricLee
    Prodigy 80 points

    Hi Eric,

    Just curious why there is a pass in shutdown. What kind of application will use this feature? Where can I find this information in the datasheet?

    Is this a design flaw so that you have a new IM5121?

  • 0 in reply to Kenny Ding
    TI__Guru 58941 points

    Hi

    Such a path from the input power supply to the output through the high-side body diode is natual in boost topology.

    All boost topology has the same issue. That's why LM5121 is developed.

    In normal boost topology, VOUT never goes below VIN.

    Regards,

     

  • 0 in reply to EricLee
    Prodigy 80 points

    I see. Is the high side switch on during shutdown? I am designing a 19V battery charger and want to make sure there is no back flow current during shutdown.

  • 0 in reply to Kenny Ding
    TI__Guru 58941 points

    Hi

    High-side switch turns off in shutdown, but still there is a path through the body-diode of the high-side MOSFET. Back flow current from the output to the input is prevended by the same body-diode of the high-side MOSFET in sShutdown.

    Regards,