LMR64010: When fz of LMR64010 became close the recommended range, behavior disstability. Is there a problem?

Hi Bob,

I'm running some simulations and will get back to you once I have the data. It makes sense that lowering the zero in the compensation will make the boost converter stable.

Thanks,

Garrett

Dear Garrett Roecker

Thank you very much for reply.

I am waitting for you reply.

Best regard.
Bob Lee.

Bob,

Are you just seeing the oscillation at 10mA load? At the maximum load current is there any instability? Looking through my calculations there shouldn't be any issue using the R1 =283k, R2=13k, and Cff= 82pF.

Thanks,

Garrett

Dear Garrett Roecker,

Thank you very much for reply.

It used the R1 =283k, R2=13k, and Cff= 82pF.
My customer confirmed oscillation at 10mA load.
It is no oscillation at maximum load current.

Why reason oscillation at 10mA load?

It used the R1 =283k, R2=13k, and Cff= 270pF~1000pF,
did not oscillation at 10mA load current.

Do not problem to use Cff= 270pF~1000pF（Fz=2.1~0.6kHz)?

Best regard.
Bob Lee

Bob,

It is okay to increase the value of the Cff capacitor. All that changing this is doing is modifying the compensation loop by slowing it down slightly. As long as all the customer load transient specs are achieved and it is stable at full load this will be okay. Oscillations in light load can happen due minimum on time pulses of the IC.

Thanks,

Garrett

Dear Garrett Roecker,

Thank you very much for reply.

Best regard.
Bob Lee.

Dear Garrett Roecker

I have a add question.
As the output current increases, the output voltage increases.

Is this normal behavior?

Measurement result

Vin[V]  Iout[mA]    Vout[V]
5.02     1.50          28.05
5.02     11.69        28.03
4.99     23.00       28.52
4.98     34.08       28.63
4.96     45.31       28.78
4.94     56.92       29.06


Best regard.
Bob Lee

Bob,

Do you have any waveforms of the output voltage for the conditions that you mention above?

Thanks,

Garrett

Dear Garrett Roecker

Thank you very much for reply.
I attached about Measurement waveform.

Could you check attached file?

Best regard.
Bob Lee.

LMR64010_Question.pdf

Bob,

I'm looking at this. I will get back to you shortly.

-Garrett

Hi Bob,

The output voltage increasing with load is very strange, normally as load increased the output voltage might decrease slightly. Please ensure that you are measuring directly across the output capcitor when the VOUT measurements are being taken. There could also be some component that is populated or the inductor might be getting saturated..

I recreated the application setup as described above on the EVM and these are the measurement I recorded


Vin(V) Iout(mA) Vout (V)
5.00 1.50 28.01
5.00 11.69 27.84
5.00 23.00 27.82
5.00 34.08 27.80
5.00 45.31 27.77
5.00 56.92 27.75

for this setup
R1 :283kΩ
R2 :13kΩ
Cff: 82pF
L :10μH
Cin: 4.7μF
Cout: 10μF


Thanks,

Garrett

Dear Garrett Roecker,

Thank you very much for measurement data.

Customer setup as
R1 :283kΩ
R2 :13kΩ
Cff: 560pF
L :10μH VLS252012CX-100M.
Cin: 4.7μF
Cout: 10μF

Cff change 560pF, for compensation loop by slowing down slightly.

The difference with customers is CFF,
Would you think different phenomenon at CFF?

Best regard.
Bob Lee.

Bob,

I believe the CFF cap is going to make a difference here. The load regulation accuracy and the current loop are related though the low frequency gain of the control loop. The higher the gain the more accurate the output should be. The CFF capacitor is setting the extra zero in the kHz range so this should no have an effect.

Are you just seeing this on one board or multiple boards?

Thanks,

Garrett

Dear Garrett Roecker,

Thank you very much for reply.

As I could not understand reply,Could you teach me?

You said
『I believe the CFF cap is going to make a difference here. 』
and
『The CFF capacitor is setting the extra zero in the kHz range so this should no have an effect.』

Which one is correct?
Is there Cff Influence of output voltage.

Thinking there is a problem with saturation of the inductor,
My customer the inductor change and confirmed.

I feedback about Board later.

Best regard.
Bob Lee.

Bob,

Sorry that was a miss type. I meant to type that "the CFF capacitor will probably not going to make a difference."

Are you saying that the customer confirmed that the inductor was becoming saturated?

Thanks,

Garrett

Dear Garrett Roecker,

Thank you very much for reply.

『Are you saying that the customer confirmed that the inductor was becoming saturated?』

Yes, My customer changed Inductor.
Situation was not change.

Is there anything else cause?

What thinking?

Best regard.
Bob Lee.

Bob,

There is currently no clear reason why this is happening. I was able to modify the EVM to match your application and I did not see the similar issue. Data was posted previously.

Did you find out if this is only present on one board? Or is it on multiple boards?

Thanks,

Garrett

Dear Garrett Roecker,

Thank you very much for reply.

I checked about board,
muliple board was same Situation.

Whereas My customer doubted layout,
Does this kind of phenomenon occur in the layout?

Best regard.
Bob Lee.