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ElectronicsLabUser

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  1. I saw the data sheet of the LTC3703 and there was a design example on page 27, i followed the same procedure.
    LTC3703 Data Sheet
    Specifications:
    VIN = 24V to 100V, VOUT = 12V, IOUT(Max) = 10A, f = 250kHz

    1. RSET
    As per the formula in the data sheet
    RSET(kOhm) = 7100/(250 - 25) = 31.5KOhm -> eq1

    2. Inductor value for about 40% ripple current at maximum VIN
    L = 12/250K*0.4*10(1 - 12/100) = 10.56uH. -> eq2

    3. Minimum On-time
    ton(min) = 12/(100*250kHz) = 480nS -> eq3
    which is above LTC3703's 200ns Minimum on-time.

    4. Top and Bottom MOSFET switch

    Since the drain of each MOSFET will see the full supply voltage 100V (max) plus any ringing, choose a 125V MOSFET to provide a margin of safety.
     

    1648979631066.png


    PMAIN = 1.32W -> eq4
     

    1648979669188.png


    = 96.4DegC.

    1648979697485.png


    =1.84 -> eq5
    TJ = 70 + 1.84*20 = 106.8

    5. Current Limit Resistor

    RDS(ON) = (25mOhm)/2 [1 + 0.009(105 - 25)] = 21.5mOhm
    IMAX pin voltage = 10*0.0215 = 0.215V
    RMAX = 0.215/12uA = 18k -> eq6

    6. CIN is chosen for an RMS current rating of 5A (IMAX/2) at 85DegC.
    7. For the output capacitor 2 low ESR OS-CON capacitors (18mF) are used.

    The LTSPICE model is in progress, i have completed to the below level, the work is still in progress, i also need to choose the MOSFET. But based on the above steps, could you please provide comments.

    design.pdf

  2. On 3/28/2022 at 7:26 AM, HarryA said:

    The circuit there is slightly different. Note it uses the FDS6680A mosfets.

    642473649_Buckconv3703.png.8899aaaaeb0a0a2821b4a08dd32e1ab1.png

    On 3/28/2022 at 7:26 AM, HarryA said:

     

    I have started going through the data sheet and trying to download ltspice simulation models for buck converter, but the above circuit i could not locate, have you created on your own? just for information.

  3. I need to design a buck converter with the following requirements, Input voltage 24V - 100V (2 - 10 Amps) and the output voltage shall be 12V (20 Amps). I started with the following circuit available in the net.

    image.png.95c14b0b719f12ee2518d9cf90721190.png

    The Diode, Inductor, Capacitor i have not yet selected, First question is how do i switch the MOSFET, do i need to interface a micro controller to calculate the duty cycle based on the output current, input voltage? I am new to hardware design. Please help.

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