• State
  • Locked Locked
  • Replies 2 replies
  • Subscribers 38 subscribers
  • Views 645 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.

Vgs max exceeded in LM5118 design

Ted Darby
Prodigy 10 points

Other Parts Discussed in Thread: LM5118, CSD16301Q2

I completed a design with webench and have been testing the boards. The design is a buck-boost power supply  with 12V, 1A out using the LM5118. Webench recommended the CSD16301Q2 transistor for the boost transistor (M2) but drives the gate with 12V. Absolute maximum rating for Vgs is +10/-8. In this design the source pin is connected directly to ground so the gate voltage = Vgs. Removing the 12V supply from Vccx lowers Vgs but makes the gate drive to the other fet marginal.

  • 0
    TI__Intellectual 2155 points

    Hi Ted,

    Thank you for bringing this to our attention.

    From the block diagram on page 10 of the datasheet, it looks like the high side gate driver is driven by either VCC or VCCX, but it is not clear what drives the low side gate driver. I am looking into this, but it may be the internal VCC, which is 5V. If that is the case, the Vgsmax rating on the boost FET may not be an error.

    If you disconnect VCCX, the high side gate will be driven by the internal VCC of 5V, which may not be enough.

  • 0 in reply to Kevin Ip
    TI__Intellectual 2155 points

    Hi Ted,

    I need to correct myself: both the buck FET gate driver (HO pin) and the boost FET gate driver (LO pin) are driven by VCCX when it is connected. If VCCX is not connected, they are both being driven by the internal VCC of 7V.

    So in your case, you may need to use a voltage divider or another external power source to power VCCX if the internal VCC of 7V is not sufficient.

    It also looks like the Vgs rating on the boost FET selection is not being accounted for properly when the Vout is greater that 7V, so this needs to be checked out.

    Again, thank you for bringing this to our attention.