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LM61460: LM61460 Inductor Selection Example Confusion

Filipe Rubinstein
Intellectual 931 points
Part Number: LM61460

Hi all,

I hope you are doing well! I have some confusion concerning the example USB-C application shown below. In this circuit operating at 500kHz, the example uses a 10uH inductor to satisfy the 5V to 20V output range. However, from equation 10 in the datasheet of the LM61460, we find that the minimum inductance needed to avoid subharmonic oscillation would be at least 0.32* VOUT/fSW. With Vout=20V, we find that we would need an inductance of at least 12.8uH to satisfy this requirement. Is the inductor in the example incorrectly used or is this more of a general guideline to follow? How much variation can we have to work around this restriction?

  • 0
    TI__Mastermind 23845 points

    Hi Filipe,

    Since you are using a higher output voltage then the minimum inductance needed is based on the equation to avoid the subharmonic oscillation. The 30% rule of peak to peak inductor ripple is more of a guidance but the subharmonic oscillation is the one that you need to avoid and it is more IC specific. 

    Therefore in your case, i would choose and inductance value of 15uH or higher. 

    Thanks

    -Arief