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LM5141-Q1: Inductor selection

takeshi.konno
Prodigy 10 points
Part Number: LM5141-Q1


I have a question about inductor selection for LM5141-Q.   I checked the required inductor value using two different ways. But I got different results. I am little confused. I would like to know which is correct way to determine the inductor value. 

- The equation in LM5141-Q1 datasheet 

According to datasheet, the required inductor value can be calculated with equation 15 in the datasheet.

For our application, the output voltage is 3.3V and maximum output current is 12A and switching frequency is 396kHz.

As you can see below, the required inductor value is more than 2.31uH.

- WEBENCH tool

I used WEBENCH tool with following input parameters. They said that the inductor value is 1.8uH.  But the 1.8uH is less than required inductor value calculated by equation in the datasheet.

- VIN = 6V to 16V, Output = 3.3V, load current = 10A, Freq = 393.267kHz, Temp=25degC, LM5141-Q1

  • +1
    TI__Guru* 76992 points

    Hi Takeshi-san,

    The expression for the inductance in the datasheet is too conservative. You can use the quickstart calculator to derive the value. Typically, setting the ripple current at 35-40% full load also aligns with the internal slope comp for typical values of the shunt resistor (i.e. OCP set at 140-150% of full load).

    Regards,

    Tim