• State Resolved
  • Locked Locked
  • Replies 2 replies
  • Subscribers 63 subscribers
  • Views 316 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.

LMR14020: How this device charge the boot cap during start-up

Gabriel Xu
Intellectual 2145 points
Part Number: LMR14020

Hi teams

As I know, high-side FET is powered by the boot cap. It means that the boot cap need to be charged before we try to turn on the high sidesFET.

However, for non-sync buck device like LMR14020, we can't directly control the diode turn on or off. How to charge the boot cap during the converter start-up?

Thanks in advance.

  • +1
    TI__Mastermind 27470 points

    HI

    for non-sync converter, there is current path from boot->SW->L->Vo, cause Cboot is smaller than Cout, so Cboot will take most of voltage for drive the high side on.

    For LMR14020, it also  integrated low side MOSFET pulls SW low to charge the BOOT capacitor.you can refer datasheet 8.3.4

  • 0 in reply to Daniel Li14
    TI__Intellectual 2145 points

    Hi Daniel

    Thanks! I found this section in datasheet. Do you mean that the integrated low side FET will turn-on to charge the boot whenever the boot UVLO have kick in? 

    Sometime when LMR14020 power off and power on again in very short period, the output cap of LMR14020 didn't completely discharge.

    If the remining cap voltage is higher than internal LDO output, the charge path on longer vaild anymore, I want to make sure even in such condition this integrated low side FET still could turn-on to charge the boot cap and solve this issue?