• State TI Thinks Resolved
  • Locked Locked
  • Replies 3 replies
  • Answers 2 answers
  • Subscribers 63 subscribers
  • Views 101 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

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.

LM5146-Q1: HO pin voltage is very high for the required MOSFET

Joselito Go
Expert 3060 points
Part Number: LM5146-Q1
Other Parts Discussed in Thread: CSD18543Q3A

Hi Experts,

Good day.

Our customer is asking if the HO pin voltage is okay to switch the required MOSFET.
Below is the attached TINA Model. I tried to simulate and get the HO output voltage and I got 56V while the required MOSFET which is CSD18543Q3A has Vgs up to 20V only.

webench_design_7473015_78.tsc

Please advise if this is okay or not.

Regards,

Josel

  • 0
    TI__Mastermind 22299 points

    Hi Josel,

    The source of the high-side FET is SW node, and SW will rise with HO.

    The gate-source voltage is the BST-SW voltage, which is charged up to ~(VCC-Vdiode) when SW is low.

    See functional block diagram in section 8.2 of the datasheet, HO driver's high-side supply is the bootstrap.

    The typical Vgs of the High side FET will be 7.5V - 0.75V = 6.75V (typical). 

    Hope this helps,

    -Orlando

  • 0 in reply to Orlando Murray
    TI__Expert 3060 points

    Hi Orlando,

    Is the simulation correct that the HO voltage is 56V? is that still acceptable to the MOSFET gate?
    Is the WEBECH recommendation correct and can be used by the customer?

    Regards,

    Josel

  • 0 in reply to Joselito Go
    TI__Mastermind 22299 points

    Hi Joselito,

    Correct. This is normal operation. 

    The MOSFET gate specs are Gate to Source. The Source of the highside FET is SW. 

    The BST capacitor is also relative to SW.

    The BST will ideally be SW+6.75V. The 6.75V is stored as charge in the BST capacitor.

    Thus as SW goes up, BST also goes up.

    When HO turns on, it is connected to BST pin. BST & HO will reach up to VIN+6.75V.

    However, the gate-to-source on HS FET will only be 6.75V.

    This is typical buck operation.

    Hope this helps,

    -Orlando