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LM3488: Sepic circuit MOS constant on during start up

George Zhao
Intellectual 1635 points
Part Number: LM3488

Hi all, 

I'm using LM3488 for a Sepic circuit. The working conditions are: Vin=5~24V, Vout=12V, Iout<=1A, fsw=300kHz. 

When at low voltage start up condition, the MOSFET is constant on and the input current is constantly too high. (See attached file. CH1 is VDR and CH2 is Iin.) 

Any advise on how this happened and how to fix it?

Many thanks!

George

  • 0
    TI__Guru* 75370 points
    Hi George,

    Something is wrong int eh circuit, because the gate driver should not stay permanent high. It must be reset each switching cycle because the max duty is limited to about 80%. Please share your schematic for an review.

    Thanks,
    Youhao Xi, Applications Engineering