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WEBENCH® Tools/LM26420: Question about inductance value

Satoshi
Guru 19585 points
Part Number: LM26420

Tool/software: WEBENCH® Design Tools

I trying to simulate Webench below condition,

--------------------------------

・Device： LM26420X（fsw： 2.2MHz）

・Vin： 4～5.5V

・Vout1： 1.2V / 1.1A

・Vout2： 3.3V / 0.6A

--------------------------------

But, for example, Vout2(3.3V) inductor's Lowerbound is 7.988μH, I feel that more small inductance is no problem.

What is the reason for inductor's Lowerbound: 7.988μH?

(Is this Webench bug?)

By the way; I hope to use 3.3μH inductor, and compensation was over 45° in the condition of 3.3μH.

Is there any problem for 3.3μH?

LM26420.pdf

Best regards,

Satoshi

  • 0
    TI__Expert 3320 points

    Hi Satoshi San,

    For this design, Inductor value is calculated by considering the peak to peak ripple as 10% of Iout (The KIND value is 0.1) for both the channels. Please see the below equation. The minimum value will be little below what the equation calculates(Typically 0.8*Lo(min)). So the 7.988uH. 

    You can reduce the inductor value to 3.3uH, but it increases the peak to peak ripple current roughly up to 30% of Iout. Kindly take this into account depending on the type of load you're driving.  

    Best Regards,

    Bhushan