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LM5001-Q1: LM5001Q1

akanksha upadhyay
Prodigy 50 points
Part Number: LM5001-Q1

Dear Sir/Madam,

I have selected the part LM5001-Q1 for  SEPIC converter  with input voltage 3.5V to 15V  and output voltage of 12V . When i am selecting the output current of 230mA on TI work Bench it says "Design update failed. Can't find suitable FET for the design. Try reducing load current This device has CC enabled but there is no circuit calculator found."

Please tell the solution

  • 0
    TI__Intellectual 2790 points

    Hi Akanksha,

    Thanks for reaching out. I'll get back to you with some feedback.

    Thank you and best regards,
    Bryan

  • 0 in reply to Bryan Radix
    Prodigy 50 points

    Hii.

    Waiting for the same.

    Thanks

  • 0 in reply to akanksha upadhyay
    TI__Intellectual 2790 points

    Hi Akanksha,

    Thanks for your patience. Is there a reason why you chose this device and not a newer device like the LM51581-Q1?
    Newer devices usually have better available design resources, like Quickstart Calculators.

    The maximum SEPIC duty cycle is calculated according to Dmax = (Vout + Vf) / (Vin,min + Vout + Vf), with Vf being the forward voltage of the diode.
    In your case, Dmax would be 0.784, assuming Vf=0.7V. While the worst case maximum duty cycle limit is given in the datasheet as being 80%.

    As you know, the device has an integrated FET, thus limiting the flexibility for applications. 
    Furthermore, in the "Designing A SEPIC Converter" - App Note, the rms current which will flow through the switch is calculated in section 4.
    Assuming the peak-to-peak ripple current to be approximately 40% of the maximum input current at the minimum input voltage, the peak switch current would equal 1.28A, which violates the 1A current limit of the integrated MOSFET.

    Thus you can't operate this device with these parameters.

    Thank you and best regards,
    Bryan