**Part Number:**LM25018

**Other Parts Discussed in Thread:**LM3150,

Hi everyone,

With a buck converter I need to obtain a stable output at 16.8V and a maximum charging current of 300mA.

Initially I started considering the LM3150, but after suggestions I was informed that the tolerance on the output values of the limiting current could even reach 50% based on various factors such as RdsON, inductance value etc..

Since I wanted an Iout limited to max 300mA and needed a simple and fairly narrow layout with easy-to-solder components, it was suggested that I use the LM25018.

So I carried out some studies on the datasheet and generated a diagram with Webench.

I then created an Excel file with the calculations relating to the LM25018 which I carried out based on what was reported in the datasheet.

If you have a chance, check it for a moment because there are a few things that don't add up to me.

I am attaching the electrical diagram that Webench generates for me, which is partly correct and partly seems to me to generate values that are not very correct.

the only difference compared to the webench scheme is the insertion of a potentiometer (after Rfbt1 which will not be 10k but 8.7K) so as to be able to more precisely adjust the output voltage to the value I want of 16.80V

My values are as follows:

VALUES PROJECT | ||

Vin min | 20 | V |

Vin nominal | 24 | V |

Vin max | 28 | V |

I out | 0,3 | A |

V out | 16,803 | V |

1) From the datasheet the fSW should have the following formula:

and therefore from the calculations it should come out at around 604 kHz with a Ron of 309kΩ, however on Webench the fSW comes out at 544 kHz (which is very similar to the fSW(max) calculated with Dmin/Ton(min) )

2) Then on WeBench he inserts an inductance of 150uH, but WeBench calculates everything based on the fSW of 543 kHz, while I get L1 of 130uH but with an fSW of 604 kHz

3) The input capacitor calculated according to the formula:

choosing an input ΔV of 0.5V (imagining that I can vary for example between 23.5V and 24.5V) the Cin comes out at 24.82uF while Webench suggests the 1uF one which is lower, why?

4) Finally I have a question precisely about the peak current: the peak current calculated according to the formula :

I find it to be 337mA which is < 390mA (which from the datasheet is the minimum current limit threshold)

So what happens if the calculated peak current is smaller than the minimum current limit threshold?

At the moment these doubts have arisen about it, I hope I'm not too wrong in order to avoid mistakes. I have already placed the PCB a bit and it seems excellent also in terms of size and space occupied.

If we can resolve these doubts, I will show you the placement, whether it is correct and whether it can create problems, asking you for suggestions on the matter.

Thank you

Paolo