I'm developing a PCB in Cadsoft Eagle as seen in the brd and sch files as per the links below:
See the images below for screenshots of the schematic and the board respectively.
My issue is with feedback I received from my board house regarding the sizes of my inductor and Cout being too small in relation to the switching frequency of my LM2575 switching regulator which as per page 7 of the datasheet is 52 kHz.
For the switching regulator sub-circuit design I carefully utilised the design procedure as per pages 13 to 18 of the LM2575 datasheet.
Based on the provided design guidance within this pages the stand out selection factors in relation to picking an inductor are:
The inductor is rated for operation with a current rating (Irating) of 1.15 x Iload whereby I load in my case is 0.4A hence Irating equals 0.46A.
The inductor is rated to operate with the LM2575 switching frequency of 52kHz.
The pages also provide inductor part numbers from three different manufacturers. Selection of the part number is based on the inductor value which in turn is based on the desired LM2575 Vout, maximum input voltage into the LM2575 and Iload. In my case my desired LM2575 Vout is 5V, my maximum input voltage is +24V and my Iload is 0.4A hence the inductor value as per the figure 28 on the LM2575 datasheet is 680uH which as per table 2 on page 16 of the LM2575 datasheet means the following inductors can be used: 67127050 from Schott, PE-52629 from Pulse Eng and RL1950 from Renco.
1st question: What exactly is wrong with the size of my current inductor selection as per my .sch and .brd files or above screenshots? I'm using an inductor of package 0805 as per the eagle package.
2nd question: Does anyone have any idea where I can find the Cadsoft Eagle library files for any of the three inductors? I feel one of these three should be of the right size in relation to the feedback from my boardhouse.
As for the selection of Cout, the design guidance within pages 13 - 18 doesn't mention anything regarding the size of the Cout capcaitor to be used. In my design as per links above, I'm utilising a standard 0805 capacitor which I have used all across my schematic.
3rd question: Any idea which Cout capacitor size I should be selecting?
Note: I would like to stick to using the LM2575 as I've gone quite far with integrating it within my design plus the availability of its Cadsoft Eagle library file.