Hi friends,
I try to build my circuit and I am not understanding the data sheet.
I attached the whole data sheet, and add the specific sections.

I need to calculate those 4 components:

The data sheet tell me to calculate "Rc" and other components through trial and error test.



I download analog design software "LTspice" and the circuit from analog website, but my graphs are completely different.

(The blue trace is I(L))

My questions are:
1. Did I understand correctly the datasheet? (by calculate the components by trial & error)
2. How can I do that? what I make wrong about their software?


Thank you very much!

 

First things first. In order to know what compensation is required you need to know what the loop response of your system is. Once you know what your loop response is you can locate the pole and the zero of the compensator to add phase margin at the unity gain crossover and add additional rolloff at higher frequencies. The reason they tell you to do it by trial and error is that it depends on your inductor L1 and the capacitor Cout and its Equivalent Series Resistance. The chip designers have less than zero knowledge of what components you might select to use with their part.

Your graph is completely different because it includes the startup sequence. What you want is a step function on the load after the device has reached steady state, which is what is being show in Figure 3., of the datasheet.

 

The startup transient is a large-signal transient that is quite different from a small-signal load-change transient.

The value of the Css capacitor connected to the SS (Soft-Start) pin controls the start-up transient.
A larger capacitor should reduce the observed overshoot upon startup

 

What are the requirements of your load?? The load determines what response is needed to deliver adequate performance. So the very first thing you need to know is what your load requires.
So let us know how critical the regulation for the load is. Then there can be some help that is not a guess.

 

This is a very good text on the subject
https://www.ti.com/seclit/ml/slup340/slup340.pdf

 

First things first. In order to know what compensation is required you need to know what the loop response of your system is. Once you know what your loop response is you can locate the pole and the zero of the compensator to add phase margin at the unity gain crossover and add additional rolloff at higher frequencies. The reason they tell you to do it by trial and error is that it depends on your inductor L1 and the capacitor Cout and its Equivalent Series Resistance. The chip designers have less than zero knowledge of what components you might select to use with their part.

Your graph is completely different because it includes the startup sequence. What you want is a step function on the load after the device has reached steady state, which is what is being show in Figure 3., of the datasheet.

Wow, Thank you very much!
I will look more information about the loop response & poles and zeros, I need to see example how its done.
I didn't succeeded to edit the Analog's circuit, I will try again later.

Thank you again .

The startup transient is a large-signal transient that is quite different from a small-signal load-change transient.

The value of the Css capacitor connected to the SS (Soft-Start) pin controls the start-up transient.
A larger capacitor should reduce the observed overshoot upon startup

Thank you, I have mistake about Css, I know is size.
The other components need to be found.
I started to find them .

This is a very good text on the subject
https://www.ti.com/seclit/ml/slup340/slup340.pdf

Thank you!
I started to read it, it seem very helpful.