LMR23630: About Entering PFM Mode

GARAM AN

Part Number: LMR23630

Hello,

I could find that entering PFM mode is when the minimum peak inductor current is under 300mA.

What is the meaning and where is the point of minimum peak inductor current exactly on the graph?

This is tested in condition of Vin=12v, Iout=0.1A.

Imax = 650mA, Imin=170mA.

0 Andy Chen over 5 years ago

Hi Garam,

Do you mean the I_peak = 650mA, I_valley=170mA on above inductor current waveform? this is still in DCM mode operation.

When device enter PFM mode, the I_peak is about 300mA typical, and pulse freq also drop quite below default freq.

B R

Andy

0 GARAM AN over 5 years ago in reply to Andy Chen

Thank you for the answer, Andy.

This is the full graph that I got, period is 14us, because it's 2us/div as you can see on the picture.

So, the switching frequency is 71kHz.

This means buck is working with PFM.

You can see the Ipeak = 650mA, Ivalley=170mA on the picture. I wonder why this is working PFM, even Ipeak is not under 350mA.

Thank you.

0 Andy Chen over 5 years ago in reply to GARAM AN

Hi Garam,

The period is 2.8us and freq is 350KHz

The yellow C1 channel has big DC offset round 250mA !! so actual peak is about 350mA .

B R

Andy

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