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LM5155： Excel Quick Start Calculator (Current Sence Resister)

user6273996
Prodigy 30 points
Part Number: LM5155

Hello,

Even if the recommended values of current sense Resistor(Rs) and external slope compensation Resistor(Rsl) are input to the selected values of Rs and Rsl in the Quickstart Calculator(Flyback Regulator), the difference between Selected Peak Current limit and Actual inductor Peak Current limit is internally corrected.Is it because the calculation is done?

Could you tell me the formula for Current Sence Resistor Selection?

Thank you,

  • 0
    TI__Guru 65200 points

    Hello user6273996,

    I am not sure that I understand your question. Please explain what you want to know.

    If no slope compensation is selected, the voltage on the CS pin and the selected peak current defines the sense resistor.

  • 0 in reply to Brigitte
    Prodigy 30 points

    hello,

    I calculated Rs based on the calculation formula in the data sheet, but the value was different from the Rs calculated in Excel Quick Start Calculator.

    Are there any calculations in Excel Quick Start Calculator that are not included in the data sheet?

    Please tell me the calculation formula of "step 3: Current Sense Resistor Selection" on Excel Quick Start Calculator.

  • 0 in reply to user6273996
    TI__Guru 65200 points

    Hello user6273996,

    With formula 10 in the datasheet, the sense resistor is calculated. If there is no slope compensation:

    Rs = 100mV / I_peak_lim, which is dependent on the transformer specifications, the switching frequency, the output power, the minimum input voltage and the reflected secondary voltage(s). Details are not planned to be shared here.

    The formulas in the datasheet are for a boost converter.