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LM5066I: Is the gate source current (20uA) is sufficient to enable the gate MOSFET rapidly ?

zakaria chmeit
Prodigy 20 points
Part Number: LM5066I


Hello,

When I am trying to compute the switching time for the gate of the MOSFET that is chosen in the application report Robust Hot Swap Design (Rev. A) (ti.com), and basing on the gate source current (20uA typ.) of LM5066I, I got 5.55ms as value of switching time (base on the MOSFET datasheet) while the calculated fault time in the application report is equal to 5.2ms!

So, my question is this logic ?! The value of gate source current (20uA typ.) is sufficient for enabling the MOSFET gate rapidly ? If no, what is the solution for this problem ?

Best regards,

Zakaria CHMEIT,  

  • 0
    TI__Guru** 106291 points

    Hi Zakaria,

    Welcome to E2E!

    Can you share the MOSFET part#

    Best Regards,

    Rakesh

  • 0 in reply to Rakesh
    Prodigy 20 points

    Hi Rakesh,

    Thank you for interesting in my question.

    The part number of the MOSFET that is used in the application report is :  PSMN4R8-100BSE.

    Best regards,

    Zakaria CHMEIT

  • 0 in reply to zakaria chmeit
    TI__Mastermind 40990 points

    Hi Zakaria,

    Hot swap controllers are not made for fast turn on. Hence, the gate driving strength is less (20μA). We need to adjust the fault timer duration in such a way the fault timer duration is more than the start-up time. Please fill out the design calculator to define the fault timer duration.

    www.ti.com/.../SLVC577

  • 0 in reply to Avishek Pal
    Prodigy 20 points

    Hello again,

    As you can see in the attached, I filled out the design calculator with same parameters and characteristics in the report application (which are already filled in the design calculator) then we obtain a fault timer of 5.2ms while the MOSFET needs approximatly 5.5ms to be turned-on (there is no a good margin?).

  • 0 in reply to zakaria chmeit
    TI__Mastermind 40990 points

    Please share the excel sheet with me. 

  • +1 in reply to zakaria chmeit
    TI__Mastermind 40990 points

    You can increase the value of the timer capacitor to 120nF. This results in 6.2ms of fault timer duration, which is more than the start-up time of 5.5ms as you calculated. There is no harm in increasing the fault timer capacitor value.