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Suggested FETs for low Vgs buck controllers

Erik Thomsen
Prodigy 40 points
Part Number: LM5148
Other Parts Discussed in Thread: LM5116

I have a design where I intend to switch from the LM5116 buck controller to the LM5148. However, the LM5148 only delivers 5 V (nominal) to the FET gates. At that voltage, most power FETs are barely alive.

All the controllers I have used before have a gate driver outout voltage around 8 - 10 V, so the 5 V gate driver in the LM5148 surprised me.

Can anyone suggest some FETs that are suitable with this buck controller? Supply voltage is 48 V (nominal), and maximum output current is 16 A. I expect to use two FETs in high-side and low-side.

Best regards, Erik

  • 0
    Prodigy 40 points

    Update:

    Okay, I might be able to go with the FETs suggested in the datasheet, as they actually has a specified maximum RDS(ON) for VGS = 4.5 V.

    However, I find it unwise to design the buck controller to generate such a low gate drive voltage, as it greatly narrows down the range of suitable FETs, and also inceases losses due to higher RDS(ON).

  • 0 in reply to Erik Thomsen
    TI__Mastermind 22302 points

    Hi Erik,

    Understood. Gate drive of 7.5V definitely will allow lower RDSON and more usable FETs.

    However 7.5V VCC will increase IQ, have higher minimum VIN, and be more difficult to externally bias VCC.

    5V VCC can lower Iq and operating input voltage, as well as increase light-load efficiency when 5V external VCCX is supplied.

    Also 5V can VCC can also be use for logic-level power good.

    If you need lower RDSON logic-level FET see NVMFS6H801NL or NVMFS6H800NL.

    Hope this helps,

    -Orlando