LM5155: Stop switching

Hi Antonie,

Thanks for reaching out with your question and for using the LM5155.

Can you please post a higher resolution image of the schematic? I am having a hard time reading the component values. What is the minimum input voltage for the design?

Taking a quick look at the layout the PGND and AGND pins should be connected directly to the exposed pad of the LM5155. This is will help to minimize the impact of noise on the LM5155.

Thanks,

Garrett

Hi Garrtet,

Thanlks for your support. Below is the schematic with a better resolution:

Hi Garrett,

The problem occurs when I increase the output current. I have an electronic load conected at the output of my circuit and when I increase the current the voltage decrease and the switching stops at one point (around 2A).

Hi Antoine,

Thanks for sending the schematic over. The component values look pretty good, the one thing that should changes is the value of C31. This should be about 100pF not  10nF.

Regarding the layout as mentioned before the PGND pin and AGND pins should be connected directly to the DAP. Please see the LM5155 boost EVM for an example. Is this only a two layer design?

Thanks,

Garrett

Hi Garrett,

This is a 4 layer PCB, see below:

-Internal layer 1 (GND plane)

-Internal layer 2 (signal planes)

-Bottom layer (signal planes again)

About the value of C31, I took it from the webench design. Was there a bug with the tool?

Thanks again for your support!

-Antoine

Antonie,

Regarding the layout, on the top layer the AGND and PGND should connect to the exposed pad. This will help reduce the possibility of ground bounce.

Please try the compensation values that I mentioned and see if these values improve the issue.

-Garrett