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Original question:

LM5148: Are there timing requirements for VIN, VCCX, and EN?

LM5148: Current requirement for VCCX

Thomas Sørensen
Prodigy 110 points
Part Number: LM5148
Other Parts Discussed in Thread: LM5116,

Hi,

I can see the HO and LO can supply several amps of peak current, which I guess is from the VCC  and CBOOT caps?

What are the requirements for an external VCCX supply in terms of current?

I have used the LM5116 and here both my FETs get fried if not using and external voltage on VCCX.

Thank you!

Br. Thomas

  • 0
    TI__Mastermind 22301 points

    Thomas, 

    The LM5148 VCC current is 170mA, much higher than LM5116, you might not need VCCX.

    Yes the peak current is only momentarily at the turn-on of the FETs, and is really handled by the VCC and bootstrap capacitors

    You should calculate the VCC current required based on QG of both MOSFETs and switching frequency:

    I_VCC = (Q1_g + Q2_g)*fsw

    The VCCX supply should meet this and also ideally the VCC current limit of 170mA.

    Hope this helps,

    -Orlando

  • 0 in reply to Orlando Murray
    Prodigy 110 points

    Hi Orlando,

    Thank you for quick answer.

    Doing a calculation of my total gate charges at 5V and with two FETs in parallel for high and low side, I get 21mA.

    So I guess I can save a regulator and just run everything from internal VCC.

    Br. Thomas