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Original question:

LM3478: Sepic mode Component Values

LM3478: how to know the value of ig of lm3478

user6015826
Prodigy 30 points
Part Number: LM3478

i see the pdf,but how to know the value of ig,

  • 0
    TI__Guru* 78100 points

    Hi user,

    Thank you for considering the LM3478. It is mentioned in the datasheet (which you just copy and pasted above) that IG=0.3A. This is the worst case lowest driver strength of the LM3478, which you need to consider in calculating losses. 

    Thanks,

    Youhao Xi, Applications Engineering

  • 0 in reply to Youhao Xi
    Prodigy 30 points

    Hi Youhao Xi,

    thank you for your reply，but i can't find the parameter  in datasheet(i see the Peak Driver Output Current(<10μs) ),can you help me find it ?

  • 0 in reply to user6015826
    TI__Guru* 78100 points

    Hi, 

    The 1A 10us is the absolute max rating.  The gate drive current usually takes much shorter duratin (~50 to 100ns).   The drive current can be as high as 1A but no characterization data is available. For losses estimation, you need to consider the worst case min peak current.  Note that the PCB trace impedance (mainly the stray inductance) along the gate drive signal path can reduce the peak current.  To be conservative, the datasheet recommends to use 0.3A. 

    Thanks,

    Youhao

  • 0 in reply to Youhao Xi
    Prodigy 30 points

    Hi Youhao Xi,

    thank you for your reply，but i can't find the parameter(0.3A)  in datasheet.

  • 0 in reply to user6015826
    TI__Guru* 78100 points

    Hi,

    Datasheet does not give the number, except for a max rating.  The text that you referred to seemed coming from the original apps engineer of this part and 0.3A was used in his calculation as being conservative.  Please follow suite.

    Thanks,

    Youhao