LM5165: PFM Inductor Calculation

Austen Fogarty

Part Number: LM5165

Hello

I am trying to calculate the required inductance for design 2 in the LM5165 datasheet using equation 19.

With the numbers given above, I am not calculating the same result.

The both the datasheet and the LM5165 Wide Vin Low Iq Buck Converter Quickstart Design Tool excel spreadsheet give the recommended inductance of 47 uH.

Why am I not calculating the same result?

Thanks

Austen

over 6 years ago

0 Timothy Hegarty over 6 years ago

TI__Guru 73502 points

Hi Austen,

For the Lf calculation, it should be as follows:

Lf = 3.3V/(350kHz*120A)*(1-3.3V/12V) = 57uH.

The quickstart file also considers MOSFET Rdson and inductor DCR, hence the slightly lower inductance recommendation.

Regards,

Tim

0 Austen Fogarty over 6 years ago in reply to Timothy Hegarty

Prodigy 20 points

Thanks Tim for your quick reply

It was a pretty obvious problem on my end, sometime it just takes a second pair of eyes.

Cheers

Austen

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LM5165: PFM Inductor Calculation