LMR14030: Variation of switching frequency

If the device is not in light load, the frequency is same in DCM and FCCM

for Rt=11.5K, the Fsw is nearly 2MHz

The frequency in DS Figure 25 is 300KHz

Hi,

Normally DCM has same Fsw as CCM operation.

At DCM mode, if the load current is decreasing and inductor current peak below 300mA, then the Fsw will be decreased with load current and chip works in Sleep mode.

Hi

Thank you for reply.

Now, I found the following thread.

e2e.ti.com/.../601985

In this thread, frequency is changing in DCM, not sleep mode.
I want to confirm that the frequency changing will happen even if in the DCM.

BestRegards

Please upload your waveform. just like the Figure 25 in DS.

Hi

It is difficult to show the waveform just like Figure 25 because I don't have sets to be measured now.

I only have following waveform at switching node at this time.

As the condition, RT = 11.5Kohm, load current is 0.25A.

Vin = 24V and Vout = 3.3V.

It looks in DCM mode and switching frequency is not 2MHz.

Please let me know if this waveform can not be obtained.


BestRegards

Hi

24V to 3.3V at Fsw=2.1MHz will trig Ton-min limitation, this also casue the switching freq foldback.

What's the inductor you use? you can try smaller inductor ( <2.2uH) to avoid Fsw decreasing,

Hi Andy

Thank you for your reply.

We set RT=16Kohm(Fsw=1.465MHz) and L is 2.2uH.

When the load current is light, Fsw is not as designed.

We can say such frequency variation is likely to occur at light load, and it is just normal operation.

Is it correct?

I want to confirm it because it seems not to be described on datasheet.

BestRegards.

Hi

I appreciate if you can reply.

BestRegards