LC Filter around DCDC_LP(36pin) of RT1020

[Edgard]

Dear an Engineer in NXP

according to EVK circuit design of RT1020, I found LC filter around DCDC_LP(36pin).
There are L1=4.7uH, C38=33uF and C39=0.22uF.

Recently, many manufactures of MLCC declared 33uF as NRND.
Especially, TDK recommended me to use 47uF. 

If I used 47uF, is it possible?

Thanks in advance

[EdwinHz]

Hi @Edgard,

If possible, we highly recomend you to stick to 33uF as showed in the EVK schematic. That said, 47uF should be OK as well.

BR,
Edwin.

[Edgard]

Dear @EdwinHz 

thanks for your replying.

I have another idea, is it possible to use 22uF + 10uF as almost 33uF?

Which is better, 47uF or 22uF+10uF ?
Or 10uF + 10uF + 10uF?  

(I think triple 10uF parallel coupling method is better...)

Kindest Regards

 Edgard

[EdwinHz · Accepted solution]

Hi @Edgard,

That would also depend on your physical constrains as well as BOM needs. It is probably easier to obtain and handle three 10uF capacitors, but it would also require more physical space on the PCB. If you have the space, I say go for triple 10uF as well. Otherwise, consider the constraints of your application and decide accordingly. If space is a big constraint, 47uF will do. On the other hand 22uF + 10uF is good tradeoff.

BR,
Edwin,

[Edgard]

Dear @EdwinHz 

I've got it!!! Thanks a lot!.

Redcently, 47uF MLCC is smaller than before. TDK recommendded me to use 2012 size 47uf replace of 33uF.

I caluculated the cut-off frequency. The switching frequency is about 1.5MHz. Then the LC filter as LPF required about 13kHz with 4.7uF and 33uF. 

If I used 47uF, the cut-off frequency might be about 11kHz. Is it trure?

Kindest Regards
 Edgard