NCP3125 ceramic capacitor application

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Veronika

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I am using NCP3125 regulator to convert 12V to 1V (4A).
On the 21 page of the datasheet there is shown Ceramic Capacitor Application Circuit Diagram, which I am going to use for my project.
So I am looking on it and cannot understand why all the values on the Figure 32 are different compared to Figure 31. For example, why 2.2uH inductor is used instead of 3.9uH? And why RF is 6.8kOhm, on the page 15 of the datasheet it is written that RF value should always be at least two times the value of R2, which is 10.2k???
I am completely confused, help me please to figure out these things.
Thank you in advance!
 

The application diagram in figure 32 are using output electrolytic capacitors.
The application diagram in figure 31 are using ceramic bulk capacitors.

Read the compensation network paragraph in the datasheet again. (page 14)
The ESL and the ESR of the output capacitor/s impact the system response, therefore the values for the feedback network etc. needs to be adjusted.
 

It is clear for compensation network. But why 2.2uH inductor is used instead of 3.9uH? The inductor value does not depend on the in/out capacitors (page 10, eq.6).
And why RF is 6.8kOhm, on the page 15 of the datasheet it is written that RF value should always be at least two times the value of R2, which is 10.2k??? Again, the capacitors do not impact on this feature.. Am I right??
 

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